Intelligence and Brain Damage in Children Acutely Irradiated in Utero
As a Result of the Chernobyl Accident
Angelina I. NYAGU, Konstantin N. LOGANOVSKY, Tatiana K. LOGANOVSKAJA,
Viktor S. REPIN* and Stanislav Yu. NECHAEV*
Department of Neurology, Institute for Clinical Radiology, Research Centre for Radiation Medicine of
Academy of Medical Sciences of Ukraine, WHO Collaborative Centre: nyagu@vent.kiev.ua*
Department of Dosimetry and Radiation Hygiene, Institute for Epidemiology and Prophylaxis of Radiation
Injures, Research Centre for Radiation Medicine of Academy of Medical Sciences of Ukraine, WHO
Collaborative Centre. 53 Melnikov Street, Kiev, 04050, Ukraine

Abstract
The objective of the study was psychometric, neurophysiological and neuropsychiatriccharacterisation of acutely prenatally irradiated children. 100 randomly selected children who were inutero (born between April 26th, 1986 and February 26th, 1987) at the time of the Chernobyl accident andtheir mothers evacuated to Kiev as well as 100 classmates of the children were examined by theWechsler Intelligence Scale for Children (WISC), electroencephalography (EEG) and clinical methods
at the age of 10–12 years old. Foetal doses in the acutely exposed group were 11–92 mSv, in thecomparison group — 0–3 mSv; foetal thyroid doses — 0.2–2 Gy and 0–0.04 Gy, respectively. The
acutely exposed group showed a lower mean verbal IQ than in the comparison group (105.3±13.1 vs.
118.1±13; p < .001) and a lower mean full scale IQ (112.1±15.4 vs. 120.9±11.5; p < .001). In addition
the followings were observed in the acutely exposed group; WISC performance/verbal discrepancies
with verbal decrements; a higher frequency of low-voltage and epileptiformal EEG-patterns and left
hemisphere lateralised dysfunction; an increase (p < .001) of δ- and β-power and a decrease (p < .001)of θ- and α-power; an increased frequency of paroxysmal and organic mental disorders, somatoform
autonomic dysfunction, disorders of psychological development, and behavioural and emotional
disorders. Cerebral dysfunction was etiologically heterogeneous. This study suggests that prenatal
irradiation at a thyroid foetal dose range of 0.2–2 Gy and a foetal dose of 11–92 mSv can result in
detectable brain damage.

BackgroundConsiderable strides have been made in the recent past in the knowledge and understanding of theeffects of ionising radiation on the developing brain. A dose of 10 mSv is postulated to cause a reduction in
IQ (intellectual quotient) of 0.3 [1]. The developing human brain is substantially more susceptible toteratogenic insults than most other embryonic and foetal structures [2].
The brain develops in 4 overlapping stages. The main developmental event of the first stage (0–7 weeks
after fertilisation) is the commencement of neuronal mitosis during which the brain produces two to threetimes the full adult complement of neurones [3]. Impaired cell division presumably gives rise to fewer
neurones and may result in dysraphic abnormalities (at 3–4 weeks), cerebellar agenesis (at 4–10 weeks) andsmall head size (at 3–12 weeks) [2].
The second stage (8–15 weeks) is the first critical period of cerebrogenesis and corresponds to the most
rapid proliferation of neuronal elements and substantial migration of neurones to the neocortex from their
proliferative zones near the cerebral ventricles [4–6]. Disturbances in cell migration may result in ectopic
grey matter and dysplasia [2]. Learning disorders and some form of mental retardation may arise fromabnormal migration [3].
202The third stage (16–25 weeks) is the second critical period of cerebrogenesis. This stage corresponds tothe progress of neuronal differentiation and synaptogenesis, and the beginning of the formation of brainarchitecture [2]. The most striking neurobiological event at this stage is programmed cell death or apoptosis,
when more than 50% of migrated neurones are eliminated prior to birth [3]. The recently proposed
neurodevelopmental theory of the genesis of schizophrenia shows that the second trimester of pregnancy is
critical, and disturbed neuronal apoptosis is considered as a key neurobiological abnormality leading toschizophrenia [7]. Programmed cell death, essential to the development of the normal brain and its adnexa,
could be accelerated or otherwise altered by ionising radiation [2].
The fourth stage (26+ weeks) indicates cell differentiation, progressive growth of dendrites and axons,
further formation of synapses and cerebral cytoarchitecture [2,8]. Synaptic development is also characterisedby distinct waves of overproduction and elimination [3]. Possible damage of thalamocortical innervation (at24–33 weeks) is indicated by abnormal cortical differentiation, and by involution of subpial granular layer (at24–38 weeks) — so-called marginal heterotopias [2].
Over the years, the Atomic Bomb Causalty Commission (ABCC) and its successor, the Radiation
Effects Research Foundation (RERF), have established several overlapping samples of individuals prenatally
exposed to the atomic bombing of Hiroshima and Nagasaki. According to the DS86 system of dosimetry
there are 1,544 clinical samples of prenatally exposed survivors from a sample of 1,599 (including 509
nonexposed persons) derived from the T65DR system of dosimetry. Severe mental retardation has beenclinically diagnosed in 30 (5 in nonexposed) children [2, 9]. Analysis of the Koga intelligence test scoresobtained in 1955 on the prenatally exposed survivors has revealed a progressive shift downwards in the
distribution of these scores with increasing exposure. There is an apparent dose-related reduction in mean IQ
for the groups irradiated in the periods 8–15 weeks and 16–25 weeks after fertilisation. This effect is stillapparent when the seriously retarded persons are excluded from the analysed population [10].
Data on the incidence of severe mental retardation as well as variation in intelligence quotient (IQ) andschool performance show significant effects on those survivors exposed 8−15 and 16−25 weeks after
ovulation. Studies of seizures also exhibit a radiation effect in survivors exposed 8−15 weeks after ovulation.
Magnetic resonance imaging of the brains of some mentally retarded survivors has revealed a large region ofabnormally situated grey matter, suggesting an abnormality in neuronal migration. Radiation-related smallhead size is related to a generalised growth retardation [11]. A recent reanalysis of the dosimetry data
indicated that the dose threshold for the development of mental retardation after intrauterine irradiation at
gestation terms of 8–15 weeks is 0.06–0.31 Gy. At gestation term of 16–25 weeks, it is 0.28 Gy [12].
The question of the increased lifetime prevalence of schizophrenia in survivors prenatally exposed toatomic bomb radiation is still open to discussion [13]. Among 1,867 prenatally exposed individuals, 18
subjects (0.96%) had developed schizophrenia later in life. The prevalence was significantly higher in thepeople exposed in the second trimester of pregnancy than in those exposed in the third trimester. The closer
they had been to the hypocentre, the higher was the prevalence. No statistically significant linear relationshipwas found [14].
Brain damage due to prenatal exposure was recognised by World Health Organisation (WHO) as apriority area in the assessment of the health consequences of the Chernobyl accident. Such acknowledgement
led to the establishment of the WHO Pilot Project «Brain Damage in Utero» of the International Programmeon the Health Effects of the Chernobyl Accident (IPHECA). Analysis of the results in three countries(Belarus, Russian and Ukraine) has shown the following:а) incidence of mild mental retardation in prenatally irradiated children is higher when compared withthe control group;b) an upward trend was detected in cases of behavioural disorders and in changes in the emotional
problems in children exposed in utero;c) incidence of borderline nervous and psychological disorders in the parents of prenatally irradiated203children is higher than that of controls.
On the basis of the investigations it was impossible to arrive at a final conclusion on the relationshipbetween an increase in the number of mentally retarded children and exposure to ionising radiation due to theChernobyl accident because of an absence of dosimetric support of the studies [15–17].
Recently some related studies have been published. Children irradiated in utero, living on theradioactively contaminated areas in Russian Federation (Tula Region, 137Cs deposition density 185–555
kBq•m-2) at the age of 1–7 years had the highest indices of mental morbidity and were more likely to display
borderline intelligence and mental retardation. This morbidity was linked by the authors to radiation [18].
In Belarussian prenatally irradiated children, especially those exposed in 8–15 weeks, there wererevealed more functional and organic disorders of central nervous system (CNS), borderline intelligencequotients (IQ) and abnormal EEG that were firstly linked to both radiation and psychosocial factors [19].
However, further these mental disorders among Belarussian children irradiated in utero were recognised as aresult of sociodemographic and socio-cultural factors only [20]. Among these children there were revealed anincreased prevalence of specific developmental speech-language and emotional disorders, as well as a lower
mean full scale IQ and more cases of borderline IQ, which did not show the existence of a dose-effectrelationships. No statistically significant distinctions in average IQ were found between the different
subgroups of children in relation to the gestational age at the time of the Chernobyl accident. The authors
attributed these disorders exclusively to unfavourable social-psychological and social-cultural factors [21]. At
the same time, the same authors concerning the same children recently reported that average IQ for the
subgroup of highly exposed children (thyroid doses more than 1 Gy) was lower in comparison with average
IQ for the whole exposed group (85.7±6.4 vs 89.6±10.2 at the age of 6–7 years, P=.014; 89.1±7.1 vs94.3±10.4 at age 10–12 years, P=.003) [22].
In contrast to the results of the WHO Pilot Project «Brain Damage in Utero» and another relevant
studies, there are three recently published papers [23–25] where the authors concluded that 1) the mental andphysical health of evacuee and non-evacuee children is similar and quite normal [23]; 2) the evacuee children(including irradiated in utero) were not different from their classmates based on data derived from objective
and on the majority of the subjective measures used to assess attention, memory, intelligence and school
performance [25]; 3) more evacuee mothers subjectively reported memory problems [25] and somatic
symptoms [23, 24] in their children than classmates’ mothers; 4) greater Chernobyl-focused anxiety is
associated with slightly poorer performance on measures of attention [25]; 5) the most important risk factors
were maternal somatization and Chernobyl-related stress [24]. However, as noted the authors, no dosimetricdata were available, and there were no normative data in Ukraine for the measures used in the study [24, 25].
In the frame of the WHO Pilot Project «Brain Damage in Utero» we have previously revealed asignificant increase of borderline and low range IQ, emotional and behavioural disorders, a decrease in high(IQ>110), as well as statistically significant higher prevalence of mental retardation (IQ<70) in Ukrainianprenatally irradiated children compared to the controls: 21 (3.9%) vs. 12 (1.6%) correspondingly (χ2=6.27;
df=1; P<.05) [16, 26]. Besides, we found that the thyroid-stimulating hormone (TSH) level grows with foetal
thyroid dose increase with the 0.3 Sv threshold [27]. The radiation-induced malfunction of the thyroidpituitary system was proposed as one important biological mechanism in the genesis of mental disorders in
the prenatally irradiated children [16, 26]. It was hypothesised that the cerebral basis of mental disorders in
the prenatally irradiated children is the malfunction of the left hemisphere limbic-reticular structures,
particularly in those exposed at 16–25 weeks of gestation, which obviously reflects developmental
abnormalities of brain structure and function as a result of interaction of prenatal and post-natal factors,
including possible radiation effects on the developing brain. It was also proposed that the left hemisphere ismore vulnerable to prenatal irradiation than the right [28].
Thus, in the majority of studies an increased prevalence of cognitive, emotional and behavioural
impairments have been revealed in prenatally children exposed as a result of the Chernobyl accident. A point204

at issue remains the contribution of prenatal irradiation of a foetus and, especially, of the foetal thyroid glandto the genesis of brain damage in these children.
The objectives of the study was the psychometric, neurophysiological and neuropsychiatric (according
to the International Classification of Disease, 10th Revision (ICD-10) criteria) characterisation of acutely
prenatally irradiated children. This study involves acutely prenatally exposed children — born between April
26th, 1986 and February 26th 1987 from pregnant women at the time of the accident who had been evacuatedfrom the 30-kilometer zone surrounding the Chernobyl NPP to Kiev — and their classmates. This sample
seems to be optimal for examination of possible distinguished effects of exposure in different periods of
cerebrogenesis.
Subjects and Methods
Design and Sample
The design was a cross-sectional assessment of children who were in utero (born between April 26th,
1986 and February 26th, 1987) at the time of the Chernobyl accident (April 26th, 1986) and their mothers who
have been evacuated to Kiev. This group was acutely prenatally exposed to both radiation and non-radiation
factors at the time of explosion, being at the Chernobyl exclusion zone and evacuation route. Inhabitants ofthe town of Pripyat (n=49,360) and railway station Yanov (n=254) were evacuated on April 27th, 1986.
Residents of the 10-kilometre zone surrounding of the Chernoby NPP (n≈10,000) were on May 2nd — 3rd,
1986. Since May 4th, 1986 stepwise evacuation of population of the 30-kilometer zone surrounding of theChernobyl NPP was began. To the middle of August, 1986 there were evacuated 90,784 people from 81
settlements of Ukraine [29].
Obviously, these acutely prenatally exposed children-evacuees from Pripyat towards Kiev are the mostadequate subcohort for comparison with the Japanese cohort prenatally exposed to the atomic bombs in
Hiroshima and Nagasaki in view of 1) acute prenatal exposure, and 2) as much as possible urbanised sample.
The WHO Pilot Project «Brain Damage in Utero» International Advisory Board estimated the numberof births to be identified in the interval between April 26th, 1986 and February 26th, 1987 in the Ukrainian
radioactively contaminated areas (including the Chernobyl exclusion zone — 30-kilometer zone surrounding
the Chernobyl NPP) as 1,400. However, when in 1993–1994 we could indeed identify 1,021 (73%) of thesechildren, only 272 (27%) of them were evacuees from the Chernobyl exclusion zone. The reduced group of
the identified prenatally irradiated children could be explained by both medical and spontaneous abortions(miscarriages) and migration. In the course of the WHO Pilot Project «Brain Damage in Utero» in Ukraine
we have examined 544 (53%) prenatally irradiated children, only 115 (21%) of which were evacuees fromthe Chernobyl exclusion zone. The reduced number of the examined children irradiated in utero could be
explained by: 1) migration and «dispersion» across Ukraine and other countries, 2) incorrect registration as
prenatally irradiated children, 3) local organisational problems, and 4) refusals to be examined.
In 1997–1998, according to the database of the National Register of Ukraine, we identified the official
cohort of prenatally irradiated children in Ukraine that consisted of 733 children, including 278 (38%)
children born from mothers who had been evacuated from the Chernobyl exclusion zone in 1986. 145 (52%)
of them live in Kiev, 133 (48%) — in 26 regions of Ukraine (3–10 children per region). Besides, we haveidentified additional 69 prenatally irradiated children-evacuees living in Kiev according to the data of theSpecialised Clinical and Epidemiological Register (SCER) of the Research Centre for Radiation Medicine(RCRM) of Academy of Medical Sciences (AMS) of Ukraine. Thus, we have identified 347 prenatally
irradiated children-evacuees including 214 (62%) living in Kiev. Among the latest there is the subcohort
consisting of 182 (85%) children-evacuees from the town of Pripyat.
From the subcohort of 182 prenatally irradiated children-evacuees from the town of Pripyat living in
Kiev we randomly selected 100 (55%) children for the study (acutely exposed group). The comparison groupconsisted of 100 gender- and age-matched children selected from the classrooms of the children of the205acutely exposed group. Children of both groups were officially included to the SCER of the RCRM of AMS
of Ukraine and were profoundly medically examined by general paediatrist, paediatrist-psychoneurologist,
paediatrist-endocrinologist, paediatrist-Ear-Nose-Throat (ENT), paediatrist-ophtalmologist, paediatristcardiologist,
paediatrist-haematologists,
paediatrist-pulmonologists,
paediatrist-gastroenterologists,
paediatrist-surgeon, paediatrist-gynecologist (for girls), and genetics using general and biochemical blood
tests, immunological tests, urine tests, coprogram, thyroid and visceral ultrasonography, electrocardiogram(ECG), electroencephalogram (EEG), rheoencephalogram (RhEG) as well as fibrogastoscopy, cardiac
ultrasonography, and magnetoresonance imaging (MRI) for diagnostic reasons. These examinations havebeen carried out at the Children Department of the Out-Patients’ Clinic of the Radiation Register of the
RCRM of AMS of Ukraine.
It should be emphasised that neuropsychiatric assessments presented here are based on neurological andpsychiatric examinations, psychometry of both children and their mothers, and conventional andcomputerised EEG, which have been carried out by us and associates at the Neurology Department of the
RCRM of AMS of Ukraine. The assessments took place in 1997–1999 when the children were 10–12 years
old.
Estimation of Prenatal Age at Exposure
The most important single factor in determining the nature of the insult to the developing brain fromionising radiation exposure is gestational age. There are possible errors in the estimation of prenatal age at
exposure. Postovulatory age is usually estimated from the onset of the last menstrual period, and adjustment
is then made for the differences between that date and the probable date of fertilisation (usually taken to be 2
weeks later). Women with irregular menstrual cycles or who miss a menstrual period could erroneously
identify the onset of their last cycle [2].
In order to avoid the aforementioned uncertainties concerning the estimation of prenatal age at the timeof the Chernobyl accident we used the adapted formulas offered for estimation of prenatal age at atomic
bombing in Hiroshima and Nagasaki [30]:Days of pregnancy (Y) = 280 — (date of birth — April 26th, 1986),
where the day of birth was obtained by interview with the mothers of the children and the mean durationof pregnancy is taken to be 280 days.
Gestational weeks after fertilisation at the time of the accident were calculated by the following
equation:
Gestational weeks (G) = (Y — 14 days) / 7 days,
where G was taken to be zero if G<0.
Dosimetry
Individual reconstruction of foetal doses, foetal thyroid doses and foetal doses on the brain has been
carried out in the Department of Dosimetry and Radiation Hygiene (Chief — Prof. I.A. Likhtariev) of the
RCRM of AMS of Ukraine. It should be stressed that individual reconstruction has been carried out for all
children of both the acutely exposed group and the comparison group because the residents in Kiev were also
exposed to the Chernobyl accident fall-outs although significantly less than evacuees.
The main sources of irradiation of pregnant women were as follows: 1) external γ-irradiation of thewhole body; 2) irradiation of thyroid by radioactive iodine isotopes; 3) internal irradiation by inhaledradionuclides; 4) internal irradiation by radioactively contaminated food. The dose depended on thesettlement, the route of evacuation, and the places of intermediate and final evacuation. The estimation ofindividual doses was carried out by the methods of retrospective dosimetry that were elaborated on the baseof measurements of the dynamic of exposure dose rate (EDR) at the settlements, analysis of 30,000 «route
sheets» (information on clear address at the settlement, the date and the time of evacuation, the route of206

evacuation, the place of intermediate and final evacuation), direct measurements of radioactive iodine content
in 10,000 evacuees, 137Cs deposition density at the place of intermediate evacuation [31, 32].
Reconstruction of foetal doses was based on reconstruction of doses of pregnant women. For estimationof foetal dose due to external irradiation the screening properties of mother’s body were taking into account,and for estimation of thyroid foetal dose — mother’s thyroid dose. Shield factor of buildings in towns was
taken to be 10, in rural settlements — 3. Behavioural factor (time fraction outside houses) for pregnant
women was taken to be 0.4.
Summarised dose on the whole foetus was taken to be equal to the dose of pregnant woman. The tissueequivalent human phantom was exposed to real Chernobyl fall-outs in order to calculate the dose on the
foetal human brain. At the places of foetal organs in the phantom LiF detectors with sensitivity 0.01 mSv
were disposed. The transfer coefficient from EDR to equivalent dose on the foetal brain (Kdbrain = 0.57•10-2
mSv per 1 mR) was obtained considering the screening effect of foetal head by mother’s pelvic bones, which
does not depend on the prenatal age [32]. Finally, the dose on the foetal brain was calculated as thesummarised dose of mother’s external irradiation multiplied by Kdbrain.
In the earliest period after the Chernobyl accident (April 26th — May, 1986) internal irradiation byradioactive iodine had the most impact on the absorbed dose forming in population. Radioiodine frompregnant woman transfers to foetus quite rapidly. The rate of transfer increases in hundreds times inproportion to the term of pregnancy. Foetal thyroid begins its functioning at about the 8–12 weeks when it
absorbs 50–70% of the whole radioiodine transferred to foetus. The radioiodine transfer rate to foetal thyroid
is maximal at about the 20–25 weeks [33]. Consequently, foetal thyroid doses were reconstructed since the
8th week after fertilisation.
Foetal thyroid doses were calculated on the base of direct measurements of radioiodine contents in
mothers’ thyroid, taking into account age and other correction factors; ratio of radioactive iodine isotopes
release from the reactor, wind speed and direction. The mean standardised thyroid dose of the adult
population of Pripyat was taken to be 0.605 Gy (standard error 7%). Protective effect of stable iodine wastaken to be 0.75. At present there are no officially adapted model for calculation of foetal thyroid dose thatcan be by 1 to 10 times larger than mother’s thyroid dose [31, 32]. Assuming that the coefficient oftransplacentar transfer of iodine is 1 and iodine concentrations in maternal and foetal structures are equal,
maternal and foetal thyroid doses were taken to be equal and not dependant on the prenatal age.

Intelligence assessment
The intellectual ability of children was assessed by the adapted and normalised version for the Ukrainianchildren of the WISC [34], which was carried out by Prof. Yu.Z. Gilbukh and colleagues from the ResearchInstitute of Psychology of Academy of Pedagogic Sciences of Ukraine [35]. The child’s performance wassummarised in three composite scores, the verbal, performance and full scale IQs, which provide estimates of
the individual’s intellectual abilities.
Testing procedures were performed at standard conditions at the Neurology Department of the SCRM of
AMS of Ukraine in a quite, adequately lit, well-ventilated room without an accompanying adult, seating andmaterials arrangement corresponded to recommendations by [34, 35] together with co-operative relationships
between the child and the examiner. The entire test was administered in a single session.
Following subtests of the WISC were used: verbal scale — information, vocabulary, similarities, anddigit span; performance scale — picture completion, block design, object assembly, and coding. We usedeight subtests only of the WISC, as manuals permit it, to predict a possible fatigue of children due tofollowing testing and examinations. The sum of subtest scaled scores on the affected scale was prorated toobtain the verbal and performance score that was used to derive the IQ score. To prorate the child’s score on
four verbal and four performance subtests we multiplied the sum of the four scaled scores by 1.25. The sums207

of verbal and performance subtest scaled scores were prorated separately and the resulting verbal andperformance scores were summed to yield the full scale IQ score. Scaled score equivalents of raw scores,
standardised to age, and IQ equivalents of sums of scaled scores for verbal, performance, and full scales wereobtained from the norms and conversion tables for Ukrainian children [35].
Cerebral electrical activity assessment
Quantitative electroencephalography (QEEG) is a set of non-invasive tools that are capable ofquantitatively assessing activity of the brain with sensitivity and temporal resolution superior to those of any
other imaging methods. The EEG power spectrum is quite stable and characteristic for healthy human beings.
At the same time many brain dysfunctions, including environmentally induced ones, can be distinguished by
QEEG with specificity of about 95% and sensitivity of 60–95% [36]. The level of sensitivity and specificity
of QEEG for brain injury (which is possible to expect in acutely prenatally irradiated children) meets thestandards of sensitivity and specificity maintained for MRI, sonograms, blood analysis, and other common
clinical diagnostic measures [37]. Thus, QEEG is one of the most adequate diagnostic technologies forassessment of radiation effects on the brain.
Neurophysiological investigations were carried out in the neurophysiological laboratory of the
Department of Neurology, RCRM of AMS of Ukraine in the first half of the day during the passive awake
state of a child. The children were nonmedicated for 3 and more days.
Brain electrical activity was recorded monopolarly using the International 10–20 System on 19 channels,
referenced to linked ears on a brain potential analyser «Brain Surveyor», SAICO, Italy. EEG were registeredat 1) passive awakeness, eyes closed — 1 min, 2) passive awakeness, eyes open — 30 s, 3) hyperventilation,eyes closed — 3 min, and 4) passive awakeness after hyperventilation, eyes closed — 1 min. Spectral
analysis of brain electrical activity was conducted. Epochs of analysis consisted of 60 seconds, and analysedfrequencies were in the 1−32 Hz range. Estimation and interpretation of conventional and QEEG activity
were performed according to Zhirmunskaya’s algorithm [38] together with paediatric EEG classic manuals[39–41].
Additional measurements
This paper focuses on intelligence and EEG assessment as well as clinical psychiatric and neurologicaldiagnostic in the children. At the same time the children were also measured by a number of psychologicaltests, analysis of which we hope to present further. For this paper these measures were used for verification ofclinical diagnosis.
Aiming to follow up the children who had been examined before, parents were asked to complete a
Russian translation of the Rutter A (2) Behaviour Rating Scale which was used in the WHO Pilot Project«Brain Damage in Utero» in 1993–1994. Parental rating assesses problems associated with health,hyperactivity, and behavioural and emotional disorders [42]. Russian translation of Achenbach’s Child
Behaviour Checklist (CBCL), the questionnaires for the children and the parents, was also used [43, 44].
Moreover, the Children Questionnaire of Neurosis (CQN) by V.V. Sednev [45], validated and standardisedfor Ukrainian children, was applied for revealing of depression, asthenia, behavioural disorders, autonomic
nervous system dysfunction, sleep disorders, anxiety, and sincerity.
Following the WHO Pilot Project «Brain Damage in Utero», mothers were also asked to complete theGeneral Health Questionnaire (GHQ-28), reflecting the level of her mental adaptation, the level of anxiety
and depression, and also social functions [46, 47]. The vocabulary subtest of the Wechsler Adult Intelligence
Scales (WAIS) was used to estimate the verbal intelligence of the mother. Moreover, posttraumatic stressdisorders (PTSD) in mothers were assessed by the Impact of Events Scale and Arousal Scale of PTSD [48],
as well as mother’s unmasking depression — by the Self-rating Depression Scale [49].
Finally, mothers were asked for demographic background, family history, educational level of the208family, social and economical status as well as they completed a standardised questionnaire on radiation
history. On the base of the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV)
Scale of Stress-Factors [50] we elaborated a standardised questionnaire on stress-factors related to theChernobyl accident that reflects a severity of real stress events (but not affective symptoms or Chernobylfocused anxiety) following the Chernobyl accident to the birth of the child. For instance, separation with thehusband and family during evacuation; absence information about the husband, participating in emergency
work at the Chernobyl NPP, and family; consumer problems at the places of evacuation; low level of medicalcare, etc.
Clinical Psychiatric and Neurological Assessment
The children of both the acutely prenatally exposed and the comparison groups were examined bystandardised clinical psychiatric interview and standardised clinical neurological examination at the
Department of Neurology, RCRM of AMS of Ukraine. The mental disorders and the diseases of the nervous
system were assessed according to the diagnostic criteria of ICD-10 (Chapter V: Mental and Behavioural
Disorders & Chapter VI: Diseases of the Nervous System). ICD-10 diagnostic was made on the base ofclinical psychatric and neurological examinations, psychometry, conventional and QEEG, taking into
account the results of the profound clinical, laboratory, and instrumental examination at the Children
Department of the Out-Patients’ Clinic of the Radiation Register of the RCRM of AMS of Ukraine, including
MRI of the brain for diagnostic reasons.
Statistical Analysis
Statistical processing included descriptive statistics, t test, Chi-square tests, relative risk (RR) assessment,
correlation and multiple regression analyses [51]. The paired t test was used to analyse data when a pair ofmeasurements was obtained on each individual [52]. The Bonferroni correction was used when multiple
statistical test were performed [53]. Statistical analysis was performed using STATISTICA 5.0 and MS
EXCEL 97 software.

209

35
30
25
P< .01

P< .01%

20

Acutely exposed group

15

Comparison group

10
5
0
0–7

8–15

16–25

26+

Weeks after fertilisation

Figure 1. Distribution of children by prenatal age at the time of explosion(April 26th, 1986)

Results
Descriptive Characteristic
The age (M±SD) was 11.3±0.4 years for the children from the acutely exposed group and 11.48±0.82
for the classmates; 54% of the evacuee children and 56% of the comparison groups were male.
Distribution of children by prenatal age at the time of the Chernobyl accident is shown in Figure 1. In
spite of a randomised procedure of the children selection, a significant reduction is found in the number ofthe children irradiated at 0–7 weeks after fertilisation in the acutely exposed group in comparison with theclassmates (14% vs. 31%; χ2=8.29; P<.01), which could be explained as the result of abortions and/or
miscarriages among pregnant women-evacuees. However, it is difficult to explain why there is also asignificant reduction of the number of the children from Kiev at 16–25 weeks after fertilisation in comparison
with the acutely exposed group (32% vs. 15%; χ2=8.04; P<.01).
Mean, standard deviation, and range of the individual foetal doses (summarised foetal dose of external
irradiation, mSv; equivalent dose on the foetal brain, mSv; cumulated thyroid foetal dose (since the 8th weeks
after fertilisation), Gy) for the two groups of children are presented in Table 1. It is clear that the children of
the two groups correspond to the subgroups of the Japanese sample [2]: prenatally exposed survivors to
atomic bomb radiation of the foetal dose category less than 0.01 Gy (n=1,201) — to the Ukrainiancomparison group, and those of the dose category 0.01–0.09 Gy (n=322) — to the Ukrainian acutely exposedgroup.
Distribution of summarised foetal dose of external irradiation, equivalent dose on the foetal brain, mSv,
and cumulated thyroid foetal dose (since the 8th weeks after fertilisation) among the children of the acutely
Table 1. Individual foetal doses.
t-test

P

M±SD
Range
M±SD
Range

Acutely exposedgroup31.9±14.4(10.74 – 92.52)
20.7±9.43(6.98 – 60.12)

21.31

<.001

21.14

<.001

M±SD
Range

0.66±0.32(0.22 – 2.04)

17.52

<.001

Dose

Value

Summarised foetal dose of
external irradiation, mSv
Equivalent dose on the foetal
brain, mSv
Cumulated thyroid foetal
dose (since the 8th weeks
after fertilisation), Gy

210

Comparison
group1.2±0.5(0 – 2.67)
0.8±0.5(0 – 2.52)
0.04±0(0.041)

100
90

Acutely exposed group80
70

Comparison group

60
%

50
40
30
20
10
0

1

11

20

29

38

47

56

65

74

83

93
Dose, mSv

Figure 2. Distribution of summarised foetal dose of
external irradiation
100
90
80

Acutely exposed group70

Comparison group

%

60
50
40
30
20
10
0

1.0

7.0

12.9

18.8

24.7

30.6

36.5

42.4

48.3

54.2

Figure 3. Distribution of equivalent doses on the foetal
brain

60.1
Dose, mSv

100
90

Acutely exposed group80
70

Comparison group

%

60
50
40
30
20
10
0

0-0.040.2-0.3

0.31-0.5

0.51-11+Dose, Gy

Figure 4. Distribution of foetal thyroid doses

exposed group are shown in Figures 2, 3 and 4, correspondingly. These foetal doses did not differ dependingon the prenatal age at the time of the accident.
As seen in Figure 4, radiation exposure to foetal thyroid was quite significant: the permissible dose limitof 0.3 Gy on thyroid [54] was exceeded in 97% of the children of the acutely exposed group, moreover, thefoetal thyroid of 17% of them was exposed to 1 Gy and more.
Among the acutely exposed group there were 5% disabled children and their disability was officiallyrecognised to be caused by the consequences of the Chernobyl accident. Except one child with haemophilia,
the four another children had neuromental disorders: moderate mental retardation (1), epilepsy (1), andencephalopathy (2). The child with haemophilia attended the school programme at home, and the child withmoderate mental retardation was institutionalised into the special boarding school. Moreover, 7% of the
211

90
80
p < .001
70

Acu tely exp osed grou p

60
50
%

Com p arison grou p

40
30
p < .001
20
10
0
1st

2nd

3rd

4 th

5th
Health group

Figure 5. Distribution of children by the health groups

children-evacuee systematically missed school and attended the school programme at home due to different
medical reasons except flu (epilepsy, paroxysmal states, behavioural problems, fatigue, headache, lack ofconcentration, exhaustion, etc). The other children attended public schools.
General health of children in the countries of the former U.S.S.R. is assessed according to the five«health groups»: the 1st health group includes absolutely healthy children; the 2nd — practically healthy
children (no complaints, but there are some subclinical symptoms revealed by profound clinical, laboratory
and instrumental examination only); the 3rd — children with chronic disease(s) in remission; the 4th —handicapped children with chronic disease(s) in exacerbation demanding active therapeutical intervention
and/or institutialisation; the 5th — handicapped children with severe chronic disease(s) in decompensation
stage demanding hospitalisation with absence of learning and self-service. As seen in Figure 5, among thechildren-evacuees there were significantly less practically healthy children (the 2nd health group) (10% vs.
36%; χ2=19.09; P<.001) and significantly more children with chronic diseases in remission than inclassmates (87% vs. 64%; χ2=14.3; P<.001) (the 3rd health group). The 3rd health group in the both groups
was predominantly comprised by chronic decompensated tonsillitis and adenoids of the 2nd–3rd severity
degree; cardiomyopathy; chronic inflammatory diseases of stomach and intestine at the stage of exacerbation;diffusive thyroid hyperplasia of the 3rd degree, euthrosis (normal thyroid functions); moderate to severe
disorders of refraction (hypermetropia, myopia, astigmatism). The conclusion about the health groups is
given by the experts of the Children Department of the Out-Patient's Clinic of the Radiation Register of the
RCRM of AMS of Ukraine. No single child from the both groups was recognised as absolutely healthy.
The acutely exposed children in comparison with the classmates had more often moderate complicationsof postnatal period, paroxysmal states, including epileptical, enuresis/encopresis at the age more than 4 years.
The evacuated mothers had more often moderate abnormalities and toxicosis of pregnancy (63% vs. 32%
correspondingly, χ2=19.27; P<.001).
In the families of the acutely exposed children in comparison with the classmates living conditions were
better; families with 2 and more children were more often; 85% of the fathers took part in the Chernobyl
accident consequences clean up; 8% of the mothers were disabled and their disability was officiallyrecognised to be caused by the consequences of the Chernobyl accident; the fathers took more alcoholic
drinks and tobacco; less number of the parents graduated a university and more — had specialised secondary
education.
According to our questionnaire on stress-factors related to the Chernobyl accident, a severity of realstress events was dramatically more pronounced in the mothers-evacuees than in the classmate’s mothers:
14.9±6.1 vs. 3±5.3, t =10.56, P<.001. Although the mothers-Kyievers had not been apparently exposed toreal Chernobyl-related stress-events (extreme situations) such as evacuation, family separation etc., in
212

contrast to the mothers-evacuees, the mothers of the both groups have quite significant symptoms ofChernobyl-related PTSD, which were more pronounced in the mothers-evacuees. Mean score of the Impact
of Events Scale and Arousal Scale of PTSD in the mothers-evacuees was 18.8±10.6 and the mothersKyievers — 14.8±9.9, t = 2.02, P<.05.
Mother’s unmasking depression estimated by the Self-rating Depression Scale was higher in themothers-evacuees than in the classmate’s mothers: 56.3±10.4 vs. 42±12.5, t=5.22, P<.001.
The mothers-evacuees had also worse than the classmate’s mothers mental adaptation and social
functions as well as more symptoms of anxiety and depression estimated by the GHQ-28: 9.6±9.6 vs. 4.8±4.9,
t=3.71, P<.001.
The verbal intelligence of the mother measured by the vocabulary subtest of the WAIS was lower in themothers-evacuees than in the mothers-Kyievers: 43.2±10.9 vs. 52.4±8.4, t = –5.09, P<.001.

Intellectual ability of children
Distribution of verbal IQ, performance IQ and full scale IQ among the children of the both groups ispresented in Table 2. Among the children of the acutely exposed group in comparison with the classmates
there were significantly more children with an average verbal IQ of 91–110 (53% vs. 22%; χ2=20.5; P<.001)
as well as significantly less of children with an high-advanced verbal IQ of 121–> (9% vs. 45%; χ2=32.88;
P<.001) and an high-advanced full scale IQ of 121–> (27% vs. 55%; χ2=16.21; P<.001).
Mean values of all verbal subtests and performance subtest — picture completion of the WISC weresignificantly lower in the acutely exposed children in comparison with the classmates (Table 3). Although themean verbal IQ, performance IQ and full scale IQ in children of the both groups were in high range, theacutely exposed group had a significantly lower mean verbal IQ (105.3±13.1 vs. 118.1±13; t=–6.94; P<.001)
and mean full scale IQ (112.1±15.4 vs. 120.9±11.5; t=–4.58; P<.001). The mean performance IQ, however,
was not significantly different (117.3±18 vs. 119.2±10.2; t=–.92; P>.05).
In spite of a similar performance IQ in the both groups, significant WISC performance/verbal
Table 2. Distribution of verbal IQ, performance IQ and full scale IQ.
Acutely exposed
IQ rangePχ2
group
Verbal IQ:<70–80
3
3.05
>.05
81–90
9
3.19
>.05
91–110
53
20.50
<.001
111–120
26
.04
>.05
121–>
9
32.88
<.001
Performance IQ:<70–80
3
3.05
>.05
81–90
3
3.05
>.05
91–11020.03>.05
111–120
27
.6
>.05
121–>
47
.08
>.05
Full scale IQ:<70–80
3
3.05
>.05
81–90
3
3.05
>.05
91–11033
3.03>.05
111–120
34
2.97
>.05
121–>
27
16.21
<.001

213

Comparison
group
0
3
22
30
45
0
0
19
32
49
0
0
22
23
55

Table 3 WISC subtests, verbal IQ, performance IQ and full scale IQ.
Comparison group
Acutely exposedt-testP
Measure(M±SD)
group (M±SD)
Verbal scale:
9.8±2.5–4.53<.001
11.4±2.5
Information
Vocabulary12.3±3.4
–6.84
<.001
15.4±3
Similarities
11,4±2.5
–4.89
<.001
13.2±2.7
Digit span
9.7±2.6–3.6<.001
11±2.5
Performance scale:
14.8±3.4
–3.46
<.001
16.2±2.2
Picture completion
Block design
12.5±3.5–1.61>.05
13.2±2.6
Object assembly
10.9±3.3–.72>.05
11.2±2.5
Coding11.7±3.2
2.55<.05
10.6±2.9
105.3±13.1
–6.94
<.001
118.1±13
Verbal IQ
117.3±18–.92>.05119.2±10.2
Performance IQ
112.1±15.4
–4.58
<.001
120.9±11.5
Full scale IQ
Note: Bonferroni corrected α-level of <.004 was used to assess statistical significance (.05 divided by 11
comparisons within measures of intelligence)

discrepancies (IQP–V = performance IQ – verbal IQ) with verbal decrements were revealed in the acutely
exposed group in comparison with the classmates: 12.1±13.8 (paired t = 8.7, P<.001) vs. 1.2±11.8 (paired t =1, P>.05); t=6; P<.001.
WISC performance/verbal discrepancies take on clinical significance at the magnitude more than 25
points [55]. According to this criterion (IQP–V>25), among the acutely exposed group there were significantly
more children with disharmoniously developed intelligence due to verbal decrements than in the comparisongroup (17% vs. 4%; χ2= 8.99; P<.01), especially among those irradiated at 16–25 weeks after fertilisation.
Among the children irradiated at 16–25 weeks after fertilisation (from acutely exposed group) there were 9
children with IQP–V>25 out of all 17 (more than 1/2).
In Table 4 intellectual development of children of both groups corresponding to different periods of
cerebrogenesis at exposure is presented. There is a tendency towards a deterioration of full scale IQ andverbal IQ, as well as an increasing of intellectual disharmony (IQP–V) in children of the acutely exposed group
who were exposed at 16–25 weeks after fertilisation. Among those irradiated at 16–25 weeks, the full scale
IQ and verbal IQ were the lowest in the acutely exposed.
There were 155 children (86 in the acutely exposed group and 69 in the classmates) who were at the 8th
and more weeks after fertilisation at the time of the accident. For 154 (98%) of these children the foetal
thyroid dose was reconstructured. IQs of the children in proportion to the foetal thyroid dose is presented inTable 5 and Figure 6. All classmates and 4 children from the acutely exposed group had the prenatal thyroid
dose in the range of 0.04–0.3 Gy. It should be noted that the dose of 0.3 Gy on thyroid was the dose limit forthe children at the time of the Chernobyl accident [54]. As it is shown in Table 5 and Figure 6, full scale IQ
and, especially verbal IQ, were reduced in dependence to the foetal thyroid dose. Performance IQ wasslightly reduced above the foetal thyroid dose of >1 Gy only.
According to the results of regression analysis, the children’s intelligence is etiologically heterogeneous(Table 6). Higher educational, intellectual, and economical levels of a family, as well as older parents at thetime of childbirth (at the examined age ranges 18–35 years for the mothers and 19–42 — for the fathers) are
the contributors towards a higher child intelligence. Higher doses of prenatal irradiation, especially foetal
thyroid dose, more severe stressogenic events and additional mother’s hazards in the prenatal period, worse
mother’s mental health, as well as childbirth problems are the contributors towards a lower child intelligence.
Foetal thyroid dose seems to be the main predictor of verbal intelligence deterioration (regression
coefficient = –.34–(–.39); P<.001) nd WISC performance/verbal discrepancies with verbal decrements

214

Table 4. Intellectual development of children corresponding to different periods of
cerebrogenesis at exposure.
Age in weeks after fertilisation

Acutely exposed
group

Comparisongroupt-test

P

–4.58
–6.94
–.92
6

<.001
<.001
>.05
<.001

–2.73
–3.26
–1.47
2.28

<.01
<.01
>.05
<.05

–1.37
–2.59
.74
3.29

>.05
<.01
>.05
<.001

–2.28
–2.88
–.75
2.62

<.05
<.01
>.05
<.01

–2.01
–3.78
.3
3

>.05
<.001
>.05
<.01

Total
Subjects
Full IQ (M±SD)
Verbal IQ (M±SD)
Preformance IQ (M±SD)
Intellectual disharmony IQP-V (M±SD)
paired tP
0–7
Subjects
Full IQ (M±SD)
Verbal IQ (M±SD)
Preformance IQ (M±SD)
Intellectual disharmony IQP-V (M±SD)
paired tP
8–15
Subjects
Full IQ (M±SD)
Verbal IQ (M±SD)
Preformance IQ (M±SD)
Intellectual disharmony IQP-V (M±SD)
paired tP
16–25
Subjects
Full IQ (M±SD)
Verbal IQ (M±SD)
Preformance IQ (M±SD)
Intellectual disharmony IQP-V (M±SD)
paired tP
26–term
Subjects
Full IQ (M±SD)
Verbal IQ (M±SD)
Preformance IQ (M±SD)
Intellectual disharmony IQP-V (M±SD)
paired t
P

100
112.3±15.4105.3±13.1
117.3±1812.1±13.8
8.7
<.001
14
110±14.7
103.9±15.3
115±14.6
11.1±12.8
3.3
<.001
30
113.1±10.9106.3±10.5117.9±1211.6±10.9
5.8
<.001
32
109.2±20102.7±15.5
114.7±23.3
12±14
4.8
<.001
24
116±13.1
108.3±11.2
121.4±1813.1±17.6
3.7
<.001

100
120.9±11.5118.1±13119.2±10.2
1.2±11.8
1>.05
31122.2±11.9119.4±13.5121.4±10.7
2±11.41>.05
26
117.6±12.5114.9±13115.6±10.5.8±12.5.3>.05
15
120.5±13.5117.1±16.2
118.3±9.7
1.3±12.6.4>.05
31
122.3±9.1
119.6±10.7120.2±9.4.6±11.8.3>.05

Table 5 Full scale IQ, Verbal IQ and Performance IQ at prenatal exposure to different thyroid
dose.
Thyroid doetal dose,
Gy

Full scale IQ,
M±SD

Verbal scale IQ,
M±SD

Performance scale IQ,
M±SD

0.04–0.3 (n=76)
0.31–0.6 (n=31)
0.61–1.0 (n=33)
1.0+ (n=14)

119.6±10.8113.3±15.2
113.2±14.9108.4±18.9116.6±12.3
106.9±12.1
105.5±12.7102.3±15.2

118.0±9.5118.0±17.9119.3±19.2
112.9±20.7

215

14 0

Full Scale IQ

130

Verbal IQ

IQ score

120

Performance
IQ

110
100
90
80
70
0.04 -0.3

0.31-0.6

0.61-1.0

1.0+

Thyroid foetal dose, Gy

Figure 6. Children intelligence in proportion to the thyroid
foetal dose

Table 6 Regression analysis of the predictors of the children’s intellectual development.
Regression
coefficient
Information subtest of WISC
Mother’s intelligence (vocabulary subtest of WAIS).21
Father’s age.20
Father’s educational level.18
Mother’s age.18
Mother’s educational level.14
Vocabulary subtest of WISC
Thyroid foetal dose–.39
Mother’s intelligence (vocabulary subtest of WAIS).36
Foetal dose–.29
Dose on the foetal brain–.29
Stress-events after the accident during pregnancy–.15
Similarities subtest of WISC
Thyroid foetal dose–.24
Mother’s intelligence (vocabulary subtest of WAIS).22
Dose on the foetal brain–.21
Foetal dose–.20
Stress-events after the accident during pregnancy–.16
Economic level of family.16
Mother’s GHQ-28–.15
Digit Span subtest of WISC
Thyroid foetal dose–.26
Mother’s intelligence (vocabulary subtest of WAIS).24
Dose on the foetal brain–.24
Foetal dose–.23
Mother’s additional hazards during pregnancy–.15
Mother’s Self-rating Depression Scale (Zung)–.15
Father’s educational level.14
Verbal IQ
Thyroid foetal dose–.34
Mother’s intelligence (vocabulary subtest of WAIS).33
Dose on the foetal brain–.28
Foetal dose–.28
Father’s educational level.16
Economic level of family.15
Stress-events after the accident during pregnancy–.14
Mother’s educational level.14
Predictor

216

F(df1, df2)

P

9.2002(1,198)
8.1679(1, 198)
6.6469(1, 198)
6.3917(1, 198)
4.0504(1, 198)

.003
.005
.01
.01
.04

25.7159(1,152)
28.9968(1,198)
18.3566(1, 198)
17.6903(1, 198)
4.6808(1, 198)

.000001.000000.00003.00004.03

8.4675(1,152)
9.7155(1,198)
9.0083(1, 198)
8.5392(1, 198)
5.1838(1, 198)
5.0957(1, 198)
4.6937(1, 198)

.004
.002
.003
.004
.02
.02
.03

10.5202(1,152)
11.8890(1,198)
11.5737(1, 198)
11.0999(1, 198)
4.8516(1, 198)
4.3983(1, 198)
4.2379(1, 198)

.001
.0007
.0008
.001
.03
.04
.04

18.7662(1,152)
24.6009(1,198)
17.2540(1, 198)
17.1946(1, 198)
4.8868(1, 198)
4.5543(1, 198)
3.9069(1, 198)
3.9227(1, 198)

.00003.000002.00005.00005
.03
.03
.049
.049

(Table 6 continued)
Regression
F(df1, df2)
coefficient
Picture completion subtest of WISC
Economic level of family.26
14.2983(1, 198)
Mother’s intelligence (vocabulary subtest of WAIS).22
10.0078(1,198)
Dose on the foetal brain–.19
7.1427(1, 198)
Foetal dose–.18
6.4733(1, 198)
Father’s age.17
6.2598(1, 198)
Father’s educational level.16
5.0650(1, 198)
Mother’s GHQ-28–.16
5.1748(1, 198)
Mother’s educational level.15
4.7358(1, 198)
Childbirth abnormalities–.15
4.3178(1, 198)
Block design subtest of WISC
Mother’s educational level.18
6.9333(1, 198)
Economic level of family.17
6.0673(1, 198)
Mother’s PTSD–.14
4.1347(1,198)
Object assembly subtest of WISC
Father’s educational level.18
6.5096(1, 198)
Economic level of family.17
6.1768(1, 198)
Mother’s intelligence (vocabulary subtest of WAIS).14
4.0587(1,198)
Coding subtest of WISC
Economic level of family.28
17.1997(1, 198)
Father’s educational level.16
5.3818(1, 198)
Mother’s GHQ-28–.14
4.0682(1, 198)
Performance IQ
Economic level of family.32
22.9500(1, 198)
Mother’s intelligence (vocabulary subtest of WAIS).23
10.6177(1,198)
Father’s educational level.218.7027(1, 198)
Mother’s educational level.175.8003(1, 198)
Disharmony of intellectual development IQP–V
Thyroid foetal dose.31
15.8215(1,152)
Foetal dose
.23
11.5167(1, 198)
Dose on the foetal brain.22
10.5278(1, 198)
Economic level of family.19
7.1229(1, 198)
Mother’s Self-rating Depression Scale (Zung).16
4.9322(1, 198)
Full scale IQ
Mother’s intelligence (vocabulary subtest of WAIS).32
22.3837(1,198)
Economic level of family.26
14.4738(1, 198)
Dose on the foetal brain–.20
8.0329(1, 198)
Thyroid foetal dose–.20
5.8691(1,152)
Father’s educational level.20
7.9749(1, 198)
Foetal dose–.19
7.5897(1, 198)
Mother’s educational level.15
4.6695(1, 198)
Verbal IQ(children exposed at 16–25 weeks after fertilisation, n=47)
Thyroid foetal dose-.39
5.7221(1,45)
Mother’s intelligence (vocabulary subtest of WAIS).42
5.8961 (1,45)
Vocabulary sutest of WISC
(children exposed at 16–25 weeks after fertilisation, n=47)
Thyroid foetal dose-.51
11.0984(1,45)
Mother’s intelligence (vocabulary subtest of WAIS).42
6.0628(1,45)
Predictor

P
.0002
.002
.008
.01
.01
.02
.02
.03
.04
.009
.01
.04
.01
.01
.04
.00005.02.04.000003
.001
.004
.02
.0001
.0008
.001
.008
.03
.000004
.0002
.005
.02
.005
.006
.03

.022
.022

.002
.02

(regression coefficient = .31; P<.001) (Table 6), especially among the children irradiated at 16–25 weeks
after fertilisation (Figure 7).
Brain electrical activity of children
The children of the acutely exposed group had significantly less age normal patterns of brain electricalactivity in comparison with the classmates (16% vs. 54%, χ2 = 31.74, p < .001) (Table 7). There were four217

Foetal thyroid dose vs. Verbal IQ
Verbal IQ= 114.07 - 15.64 * Foetal thyroid dose
Correlation: r = -.3895; p = .023
140
130
120

Verbal IQ

110
100
90
80
70
60
1.6

2.0

Regression
95% confid.

1.6

2.0

Regression
95% confid.

50
0.0

0.4

0.8

1.2

Foetal thyroid dose, Gy

Foetal thyroid dose vs. Vocabulary subtest of WISC
Vocabulary = 15.103 - 5.130 * Foetal thyroid dose
Correlation: r = -.5075; p = .002
20

16

Vocabulary

12

8

4

0
0.0

0.4

0.8

1.2

Foetal thyroid dose, Gy

Figure 7. Relationships between Verbal IQ and Vocabulary subtest of WISC vs foetal
thyroid dose, in children of the both groups (n=47) exposed at 16–25 weeks after
fertilization.
abnormal EEG-patterns in the prenatally irradiated children as follows:(1) Low-voltage EEG (20–25 µV) with excess of slow (δ) and fast (β) activity together withdepression of α- and θ-activity with paroxysmal activity shifted to the left fronto-temporal region was one of
the most distinguished conventional EEG-pattern in the children of the acutely exposed group (31% vs. 8%,
χ2=16.85, P<.001).
(2) Disorganised slow EEG-pattern with δ-activity domination characterised by disorganised activityof moderate (40–55 µV) or high (70–80 µV) amplitude with a mainly δ-range slow activity domination andnon-regular α-activity where hyperventilation led to bilateral paroxysmal activity discharges, as well as 3)
disorganised EEG-pattern with paroxysmal activity, similar in general to the one described above, butcharacterised by generalised paroxysmal discharges and bursts of acute, θ- and δ-waves of high amplitude
where the hyperventilation led to the bilateral paroxysmal activity increase, were found equally in the bothgroups.
(4) Epileptiformal EEG with «spike» or «polyspike—wave» complexes in the fronto-temporal region,
218

Table 7 Conventional EEG-patterns.
Acutely
exposed
group
16
0
10
6
84
31
16
20
17
73
37
15
21

EEG-pattern
Age norm
Organised
Disorganised with predominance of α-activity
Hypersynchronous
Abnormal
Low-voltage
Disorganised slow
Disorganised with paroxysmal activity
Epileptiformal
Interhemispheric asymmetry
Left hemisphere lateralised dysfunction
Right hemisphere lateralised dysfunction
Cross-hemispherical dysfunction

χ2

PComparison
group

31.74
4.08
5.36
17.15
31.74
16.85
.16
.27
15.63
24.8
15.36
.87
11.32

<.001
<.05
<.05
<.001
<.001
<.001
>.05
>.05
<.001
<.001
<.001
>.05
>.001

54
4
22
28
46
8
14
23
1
38
13
20
5

mainly of the left hemisphere, and bilateral paroxysmal activity in the form of δ-waves of very highamplitude (higher than 100 µV) was another of the most distinguished conventional EEG-pattern among thechildren of the acutely exposed group (17% vs. 1%, χ2=15.63, P<.001).
Interhemispheric asymmetry of the EEG was revealed significantly more often in the acutely exposedchildren compared with the classmates (73% vs. 38%, χ2=24.8, P<.001) according to an asymmetry index>5%. An increase of the abnormal or/and a decrease of the normal EEG-signs in one hemisphere incomparison with another were the criteria adopted for the lateralised dysfunction detection (Table 7). Threetypes of interhemispheric asymmetry were found in the children of the both groups. A left hemisphere
lateralised dysfunction was characterised by slow and/or epileptiformal activity in the fronto-temporal region
together with α-activity depression in the left hemisphere. The left-hemispherical type of EEG-laterality was
found more often among the acutely exposed children in comparison with the classmates (37% vs. 13%,
χ2=15.36, P<.001). A right hemisphere lateralised dysfunction characterised by abnormal activity in the rightfronto-temporal region did not differentiate the acutely exposed children from the classmates (15% vs. 20%,
χ2=0.87, P>.05). We described a so-called cross-hemispherical dysfunction, which consisted of abnormal
activity simultaneously in the fronto-temporal region of one hemisphere and in the parieto-temporal region ofanother hemisphere. This was found in 21% of the children from the acutely exposed group and 5% of thechildren from the comparison group (χ2=11.32, P<.001).
According to the spectral EEG-analysis, a significant difference was found between the acutely exposed
and the comparison groups (Table 8). The acutely prenatally irradiated children were dramaticallydistinguished from the classmates by an increase (P<.001) of δ- and β-power and a decrease (P<.001) of θand α-power. However, the pattern of summarised EEG spectral power in the children of the both groups
exposed at 0–7 and 26+ weeks after fertilisation was statistically equal (except more δ-power among thoseacutely exposed at 26+ weeks). The children prenatally acutely exposed at 16–25 weeks of gestation had themost distinguished pattern of summarised EEG spectral power (increased δ- and β- and decreased θ- and αpower), as well as those exposed at 8–15 weeks (increased δ- and decreased θ-power) in comparison with theclassmates.
Obviously, children’s pattern of cerebral electrical activity is, like intelligence, etiologicallyheterogeneous. On the basis of correlation and regression analyses we found that the children’s EEG-pattern
was associated with age, current neuropsychiatric disorder, perinatal pathology, mother’s mental health, aswell as exposure to the disaster — both to stress and radiation. Foetal dose was the predictor for an increase219

Table 8 EEG spectral analysis.
Age in weeks after
fertilsation

Acutely exposed
p
t
group
Summarised δ (1–4 Hz)-power (%)
All
47.65±12.54
8.65
<.001
0–7
44.99±10.71
3.2
=.001
8–15
48.53±15.03
4.25
<.001
16–25
49.81±13.10
5.46
<.001
26–term
45.05±8.41
4.01
<.001
Summarised θ (4–7) –power (%)
All
15.96±5.61
–8.9
<.001
0–7
16.75±6.08
–3.05
<.01
8–15
17.76±7.04
–4.99
<.001
16–25
14.01±4.05
–8.47
<.001
26–term
15.89±4.68
–3.12
<.01
Summarised α (7–12) –power (%)
All
26.62±10.24
–5.5
<.001
0–7
29.79±12.77
–1.07
>.05
8–15
24.55±7.88
–3.12
<.01
16–25
25.25±11.63
–3.36
<.001
26–term
29.31±8.37
–2.55
<.01
Summarised β (12–32) –power (%)
All
16.49±6.42
4.28
<.001
0–7
15.86±7.13
1
>.05
8–15
14.97±7.72
1.48
>.05
16–25
17.76±5.8
3.7<.001
26–term
17.09±7.06
2.27
<.01
Note: Bonferroni corrected α-level of <.001 was used to assess statistical significance.

Comparison group33.59±10.34
33.36±12.51
32.98±12.34
34.05±8.1733.99±10.12
23.32±6.07
23.12±7.2726.35±5.84
23±3.79
21.09±6.4233.50±7.17
33.7±8.28
30.93±7.3933.74±6.95
35.42±7.85
13.33±3.63
13.94±2.75
12.75±2.59
13.2±3.1
13.92±4.63

of summarised δ-power (regression coefficient =.46; P<.001) and β- power (regression coefficient =.22;
P=.002), and for a decrease of θ- power (regression coefficient =–.48; P<.001) and α-power (regression
coefficient =–.35; P<.001) (Table 9). This dose-effect relationship was the most pronounced in the children
exposed at 8–25 weeks, especially at 16–25 weeks after fertilisation. Thyroid foetal dose was also thepredictor for an increase of summarised δ-power (regression coefficient =.49; P<.001) and for a decrease of
θ- power (regression coefficient =–.5; P<.001) and α-power (regression coefficient =–.32; P<.001). This
dose-effect relationship was the most pronounced in the children exposed at 16–25 weeks after fertilisation(Figure 8).
The correlations between intelligence and spectral power of EEG were revealed as follows. Full scale IQ
deterioration was associated with an increase of δ-power (r=.25–.35; P<.001), especially at the left frontal
region (r=.31–.35; P<.001), a decrease of α-power (r=.27–.36; P<.001), especially at the left parieto-occipitalregion (r=.33–.36; P<.001), as well as a lateralisation of β-power to the left fronto-temporal region (r =.2;
P=.02).
Verbal IQ deterioration was associated with an increase of δ-power (r=.25–.41; P<.001), mainly in theleft hemisphere, especially at the left frontal region (r=.38–.41; P<.001), a decrease of α-power (r=.22–.38;
P<.001), also mainly in the left hemisphere, especially at the left frontal region (r=.34–.38; P<.001), as wellas an increase of β-power (r=.27; P<.001). Performance IQ deterioration was associated with an increase of
δ-power (r=.15–.28; P<.001), mainly in the right hemisphere, especially at the right parietal region (r=.21–.28; P<.001), a decrease of α-power (r=.17–.26; P<.001), also especially at the right parietal region (r=.23–.26; P<.001), as well as an increase of β-power (r=.21–27; P<.001) at the right temporal region. WISC
performance/verbal discrepancies with verbal decrements were associated with lateralisation of δ-power
towards the left parietal region (r=.24; P=.04), a decrease of θ-power in the left fronto-temporal region
220

Table 9 Relationships between EEG and doses of prenatal irradiation.
Age in weeks after
fertilsation
All
0–7
8–15
16–25
26–term

All
0–7
8–15
16–25
26–term

All
0–7
8–15
16–25
26–term

All
0–7
8–15
16–25
26–term

Regression
F(df1, df2)
coefficient
Summarised δ (1–4 Hz)-power (%)
Thyroid foetal.49
61.2214(1,152)
Foetal.4654.5663(1,198)
Foetal.4512.7301(1, 43)
Thyroid foetal.43
11.3462(1,54)
Foetal.4210.7512(1,54)
Thyroid foetal.49
15.6218(1,45)
Foetal.46
13.3483(1,45)
Thyroid foetal.54
18.6339(1,53)
Foetal dose.49
13.91842(1,53)
Summarised θ (4–7) –power (%)
Thyroid foetal–.564.3190(1,152)
Foetal–.48
60.3387(1,198)
Foetal–.34
6.9570(1, 43)
Thyroid foetal–.51
17.2614(1,54)
Foetal–.53
19.1616(1,54)
Thyroid foetal–.63
32.0500 (1,45)
Foetal–.5926.8140(1,45)
Thyroid foetal–.43
10.2321(1,53)
Foetal dose–.44
11.0047(1,53)
Summarised α (7–12) –power (%)
Thyroid foetal–.32
22.9415(1,152)
Foetal–.35
27.0970(1,198)
Foetal–.26
3.6292(1, 43)
Thyroid foetal–.26
3.5650(1,54)
Foetal–.31
5.3726(1,54)
Thyroid foetal–.35
6.7276(1,45)
Foetal–.39
8.6232(1,45)
Thyroid foetal–.39
8.2347(1,53)
Foetal dose–.3
4.4584(1,53)
Summarised β (12–32) –power (%)
Thyroid foetal.14
3.7750(1,152)
Foetal.229.9334(1,198)
Foetal.09
0.4783(1, 43)
Thyroid foetal.110.6035(1,54)
Foetal.232.8587(1,54)
Thyroid foetal.14
0.944(1,45)
Foetal.446.6197(1,45)
Thyroid foetal.17
1.3397(1,53)
Foetal dose
.11
0.5989(1,53)Dosep.000000.000000
.0008
.001
.002
.0002
.0006
.00009.0005.000000.000000.01.0001.00006.000001.000004.002.002.000003.000000
.06
.06
.02
.01
.005
.006
.04
.05
.002
.5
.4
.1
.3
.01
.2
.4

(r=.27–31; P<.001), as well as an increase of β-power (r=.2–.27; P<.001).
Although intelligence is an integrative function of the human brain, full scale IQ and, especially, verbal
IQ are closer associated with the left hemisphere functions, whereas performance IQ — with the righthemisphere ones. According to the data obtained a possible cerebral basis of full scale IQ and verbal IQ
deterioration as well as WISC performance/verbal discrepancies with verbal decrements in the prenatally
irradiated children is dysfunction of the left frontal, temporal and parietal lobes. This dysfunction apparently
involves the cortico-limbic system, prefrontal cortex (frontal associative area), the secondary cortical receptor
fields (temporal associative area), and the tertiary parietal associative area at the left, dominating, hemisphere[56, 57].
It seems to be possible to attribute this central nervous system dysfunction to prenatal exposure toionising radiation, especially at the second critical period of cerebrogenesis (16–25 weeks after fertilisation)
221

Thyroid foetal dose vs. Summarised Delta-power (%)
Delta-power = 38.689 + 14.172 * Thyroid foetal dose
Correlation: r = .49167, p = .00000
80
70

Delta-power, %

60
50
40
30

2.0

Regression
95% confid.

2.0

Regression
95% confid.

20
0.0

0.4

0.8

1.2

1.6

Thyroid foetal dose, Gy

Thyroid foetal dose vs. Summarised Theta-power (%)
Theta-power = 20.457 - 7.417 * Thyroid foetal dose
Correlation: r = -.6288; p = .00000
28
24

Theta-power, %

20
16
12
8
4
0.0

0.4

0.8

1.2

1.6

Thyroid foetal dose, Gy

Figure 8. Relationships between summarised δ (1–4 Hz)-power (%) and summarised θ (4–7) –power (%) vs. foetal thyroid dose, in children of the both groups (n=47) exposed at 16–25
weeks after fertilization.
— the time of the most sophisticated events of brain creation, as well as limbic system, brain asymmetry andhemisphere dominating forming [58–60]. Moreover, radiation-induced malfunction of the foetal thyroidpituitary system cannot be excluded.
ICD-10 diagnosis
According to the ICD-10 clinical descriptions and diagnostic guidelines, neurological disorders wererevealed in 65 of the children of the acutely exposed group and in 25 of the classmates (χ2=27.85; P<.001)(Table 10). The overwhelming majority of this pathology were episodic and paroxysmal disorders, whichwere revealed significantly more often in the acutely exposed group than in the comparison group (61% vs.
29%; χ2=20.69; P<.001). The children-evacuee had significantly more epilepsy (G40) and migraine (G43)
than the classmates. Epilepsy and other paroxysmal disorders were verified by clinical EEG, when clinicalpattern of episodic or paroxysmal disorder corresponded to paroxysmal brain electrical activity (spikes,
spike-waves, acute and slow waves of high amplitude >100 mkV).

222

Mental and behavioural disorders according to the ICD-10 criteria were revealed in 90 of the children of
the acutely exposed group and in 52 of the classmates (χ2=35.97; P<.001) (Table 10). Organic, including
symptomatic, mental disorders (F06, F07), somatoform autonomic dysfunction (F45.3), disorders of
psychological development (F80–F89), and behavioural and emotional disorders with onset usually occurringin childhood and adolescence (F90–F98) were diagnosed significantly more often in the acutely exposedgroup than in the comparison group. Mental comorbidity was 24% in the acutely exposed group and 7% in
the comparison group (χ2=11.03; P<.001).
Organic mental disorders were verified by Brain Mapping of QEEG and Visual Evoked Potentials(VEP) and in a number of cases by MRI and CT. Two cases of F07 (Personality and behavioural disorders
due to brain disease, damage and dysfunction) and 6 cases of F06 (Other mental disorders due to brain
damage and dysfunction and to physical disease) from the acutely exposed group were due to epilepsy (G40),
while 1 of F06 from the comparison group was due to epilepsy. Two cases of F07 from the acutely exposedgroup were linked to mental retardation (F70 and F71). One case of F07 and 14 cases of F06 from the acutely
exposed group, as well as 5 cases of F06 from the comparison group were attributed to the evidences ofperinatal, predominantly pre- and intrenatal, pathology, i.e. pathology during in utero period and delivery,such as moderate to severe toxicosis of pregnancy, uterine haemorrhage during pregnancy, risk of
miscarriage, waterless period during delivery, too short- or too long-time period of delivery, hypoxia of
foetus and asphyxia of newborn.
The more severe neuropsychiatric disorders — mental retardation, epilepsy, and organic mental
Table 10 Diseases of the nervous system, mental and behavioural disorders according to the ICD10 criteria.
Acutely
exposedχ2
group
Diseases of the nervous system (G00—G99)
Without neuropathology
38
27.85
Episodic and paroxysmal disorders (G40—G47):
61
20.69
G40 Epilepsy
8
5.7
G43 Migraine
88.33
G44 Other headache syndromes
36
3.43
G47 Sleep disorders
92.06
G90.8 Other disorders of autonomic nervous system
5
5.13
Mental and behavioural disorders (F00—F99)
Without psychopathology
10
35.07
Organic, including symptomatic, mental disorders (F00–F09):25
13.78
F06 Other mental disorders due to brain damage and20
8.66
dysfunction and to physical disease
F07 Personality and behavioural disorders due to
5
5.13
brain disease, damage and dysfunction
F12 Mental and behavioural disorders due to use of1
1.01
cannabinoids
Neurotic, stress-related and somatoform disorders (F40–F48):36
0.56
F45.3 Somatoform autonomic dysfunction
23
10.04
F48.0 Neurasthenia
13
4.01
F51 Nonorganic sleep disorders
6
2.08
Mental retardation (F70—F79):2
2.02
F70 Mild mental retardation
1
1.01
F71 Moderate mental retardation
1
1.01
Disorders of psychological development (F80–F89)
12
12.77
Behavioural and emotional disorders with onset usually33
4.34
occurring in childhood and adolescence (F90–F98)
Mental comorbidity24
11.03
ICD-10 code

223

P

Comparison group

<.001
<.001
<.05
<.05
>.05
>.05
<.05

75
29
1
0
24
4
0

<.001
<.001

48
6

<.01

6

<.05

0

>.05

0

>.05
<.01
<.05
>.05
>.05
>.05
>.05
<.001

31
7
24
2
0
0
0
0

<.05

20

<.001

7

disorders — were diagnosed in 25 acutely exposed children and in 6 classmates (χ2=13.78; P<.001). The
majority (16) of the acutely exposed children with these disorders (including 2 cases of mental retardation)
were irradiated at 8–15 and 16–25 weeks after fertilisation. Thyroid foetal dose of these children with severe
neuropsychiatric disorders was significantly higher than in other children of the acutely exposed group(.78±.31 vs. .59±.28, t = 2.79, P<.01).
It is clear that the children’s neuromental disorders are etiologically heterogeneous. Higher economicallevel of a family, better somatic health of a child, better mental health of parents are the contributors towards
a better children’s neuromental health. Higher doses of prenatal irradiation, especially foetal thyroid dose,more severe stress events, and additional mother’s hazards in the prenatal period, worse mother’s mental
health, as well as problems of the perinatal period are the contributors towards children’s neurological andmental health deterioration.
Discussion and Conclusions
The UNSCEAR Report-2000, Annex J: Exposure and Effects of the Chernobyl Accident [61] touched
the problem of the psychological development of the children who were exposed to radiation from the
Chernobyl accident in utero basing on one publication only [21] where cognitive, emotional and behaviouraldisorders in prenatally irradiated children were attributed exclusively to unfavourable social-psychologicaland social-cultural factors.
The WHO Pilot Project «Brain Damage in Utero» International Advisory Board assumes that prenatal
exposure to the Chernobyl disaster can give rise to a dysfunctional child, either because of organic damage tothe developing brain or because of the disturbed psychosocial milieu. Indeed, intelligence peculiarities,
neurophysiological abnormalities, and neuromental health deterioration in the children acutely prenatally
exposed to both radiation and stress are etiologically multifactorial. Although the children were affected bymultiple exposure including prenatal stress and current social, economical and medical problems in theirfamilies, the «dose—effects» relationships concerning both intelligence and EEG-parameters, which are themost marked at the critical periods of cerebrogenesis, testify to significant contribution of prenatal irradiation
into the brain damage.
This study confirms and develops the results of the WHO Pilot Project «Brain Damage in Utero» [15,17] and relevant studies [18–22] concerning mental health and intelligence deterioration in children exposed
in utero as a result of the Chernobyl disaster. Unlike to the study [21] where the authors did not findevidences of the contribution of prenatal irradiation on the children’s intelligence deterioration, we have done
it. The differences between the results of the study [21] and ours we can explain by the followings: 1)
different sample: we examined acutely exposed in 1986 children, but they — those resettled in 5–7 years
after the disaster, and 2) different measures: they analysed full scale IQ only, but we — verbal IQ (including
subtests), performance IQ (including subtests), WISC performance/verbal discrepancies, and full scale IQ.
Exactly deterioration of verbal IQ and WISC performance/verbal discrepancies with verbal decrements, werein proportion to the foetal thyroid dose.
Our data do not confirm the results of the studies [23–25] concerning similarity and normality of mental
and physical health, intelligence similarity of acutely prenatally exposed children in the Chernobyl exclusionzone evacuated to Kiev and children-classmates living in Kiev, as well as that the most important risk factors
were maternal somatization and Chernobyl-related stress. A possible explanation of the differences between
the results of the studies [23–25] and ours study seems to be as follows: 1) Restricted neuropsychologicalbattery for children’s intelligence assessment allowed them [25] to measure spatial intelligence only, which
indeed looks likely to be intact; 2) An absence of clinical neuropsychiatric examination by ICD-10 or DSMIV criteria and screening-like physical examination in the works [23, 24] resulted their conclusion concerning
evacuee children’s mental and physical welfare to be the point at issue. 3) Inadequate using of gestation
months for analysis, but not periods of cerebrogenesis (0–7, 8–15, 16–25, and 26+ weeks after fertilisation),224

and possible uncertainties in the gestation term estimation did not enable in the studies [23–25] to estimate
the most important factor in determining the nature of the insult to the developing brain from ionisingradiation [2] — exposure in critical and «non-critical» periods of prenatal development. 4) An absence of
dosimetric data for both children-evacuee and non-evacuee did not enable them [23–25] to study a possible
dose-effect relationship and to estimate the contribution of ionising radiation towards intelligence andpsychological development of the children. However, the most important reason of the differences between
their and our studies seems to be the different paradigms of the researches: psychosocial model of the studies[23–25], and neuropsychiatric or neurobilogical — in us.
It should be noted limitations and uncertainties of this study. First of all, there is a problem ofrepresentativeness of the sample: a possible bias towards «improving selection» where some disabledchildren due to neuropsychiatric problems could be dropped out from the study, or «deteriorating selection»
when for instance prodigy infants attending special advanced schools were also out of the sample. Ideally, allparentally exposed children, or at least all those who had been evacuated from the Chermobyl exclusion zone,
should be involved in the study. However, our sample — evacuee in Kiev and non-evacuee classmates living
in Kiev — looks quite good from the point of view of similarity about informational and urban saturation
environment, providing as much as possible in Ukraine. It should be also stressed that the uncertainties ofindividual doses estimation are due to an absence at present of generally accepted methodology concerningmodel of foetal dose assessment. Probably, like in Japan, there will be further new dosimetric systems andreassessment of psychometrical, neurophysiological and other data.
As it was mentioned above, our sample corresponds to subgroups of the Japanese sample [2]: prenatally
exposed survivors to atomic bomb radiation of the foetal dose category less than 0.01 Gy (n=1,201) — to the
Ukrainian comparison group, and those of the dose category 0.01–0.09 Gy (n=322) — to the Ukrainian
acutely exposed group. However, there is an extremely important radiological difference between theJapanese and Ukrainian samples — prenatal exposure to radioactive isotopes of iodine. The prenatally
exposed to atomic bomb radiation had not been irradiated by radioiodine, but the prenatally exposed children
as a result of the Chernobyl disaster received quite significant foetal thyroid doses. This fact makes difficult
to extrapolate all data (risks, thresholds of the effects, etc.) from the Japanese sample on the Chernobyl one. It
seems that the acutely prenatally exposed children at the Chernoby exclusion zone is a unique sample thatshould be used for reassessment of risks of prenatal irradiation at radiation accidents on nuclear reactors.
The results of this study agree with the Japanese studies concerning 1) dose related full scale IQ
reduction [10], 2) an increase of paroxysmal disorders [62], 3) critical periods of cerebrogenesis — 8–15 and,especially, 16–25 weeks after fertilisation [2]. The highest vulnerability of the brain under exposure at 16–25,
but not 8–15 weeks after fertilisation as in the Japanese sample, we can explain by 1) maximal radioiodinetransfer rate in foetal thyroid at about 20–25 weeks [33], 2) more «delicate» examination of intelligencedisturbances that corresponds exactly to the events of the brain creation at 16–25 weeks after fertilisation(neuronal differentiation, limbic system and brain asymmetry forming, apoptosis beginning etc. [58–60]). An
absence of dramatic increase of mental retardation, especially its severe form, as well as microcephalia
obviously can be explained by significantly lower foetal doses of irradiation than that in the atomic bomb
survivors.
Following recommendations of Shull & Otake [63] concerning future studies of the prenatally exposed
survivors and the WHO Pilot Project «Brain Damage in Utero» International Advisory Board for the second
phase of the project, we used QEEG and WISC. This resulted in interesting findings of verbal IQ reduction
and WISC performance/verbal discrepancies with verbal decrements, which were in proportion to the foetal
thyroid dose, especially among those children exposed at 16–25 weeks after fertilisation. Previously wereported [16, 26, 27] about TSH level grows with foetal thyroid dose increase with a 0.3 Sv threshold.
Probably, these children had been affected by intrauterine hypothyroidism that resulted in intelligencedisturbances during their life. Obviously, an international psychoendocrine study should be organised for225exploration of functions of the pituitary-thyroid system as a possible biological basis of mental healthproblem in children irradiated in utero as a result of the Chernobyl disaster.
The prenatally acutely exposed children have quite distinguished pattern of summarised EEG spectral
power (increased δ- and β- and decreased θ- and α-power), in comparison with both the classmates andliterature normative data [41, 55]. Foetal dose and thyroid foetal dose were the predictors of this QEEGpattern, especially among the children irradiated at 16–25 weeks after fertilisation.
Neurophysiological abnormalities together with intelligence disturbances, both dose-related, especiallyat 16–25 weeks after fertilisation, as well as a «concentration» of the most severe neuropsychiatric disorders
among the children exposed at the critical periods of cerebrogenesis, can testify to the developing brain
abnormalities due to multiple factors including the effects of prenatal irradiation.
Verbal IQ deterioration together with lateralisation of abnormal electrical activity to the left hemisphere
supports our previous report about the predominance of the left hemisphere dysfunction in prenatally
irradiated children [28]. Association of verbal IQ and left hemisphere is well-known [64], and full scale IQ iscloser related to the left than to the right hemisphere [56]. It seems that the left hemisphere is more vulnerable
to exogenous impacts including ionising radiation than the right hemisphere, probably due to dominating of
the left brain and, consequently, its more functional activity.
A possible cerebral basis of intelligence disturbances in prenatally irradiated children is dysfunction of
the left frontal, temporal and parietal lobes, involving the cortico-limbic system, prefrontal cortex, temporal
associative area, and the tertiary parietal associative area at the left dominating hemisphere [56, 57]. However,the predominance of the left hemisphere dysfunction is leading towards higher risk of schizophrenia
spectrum disorders in prenatally irradiated children, which is why the long-term follow up study of thiscohort is of great importance for clinical medicine and neuroscience.
Thus, the neuromental health of the acutely prenatally irradiated children at the Chernobyl exclusionzone is deteriorated in comparison with the non-evacuee classmates living in Kiev due to more frequent
occurrences of episodic and paroxysmal disorders, organic, including symptomatic, mental disorders,somatoform autonomic dysfunction, disorders of psychological development, and behavioural and emotional
disorders with onset usually occurring in childhood and adolescence. Obviously, their neuromental healthdisorders are etiologically heterogeneous including psycho-social and economic factors, medical problems intheir families. The effect of real stress events (but not only their perception) during pregnancy together withprenatal irradiation cannot be excluded.
Intelligence of the acutely prenatally irradiated children is deteriorated due to reduction of full scale andverbal IQ, as well as WISC performance/verbal discrepancies with verbal decrements. Although thechildren’s intelligence is multifactorial, the contribution of prenatal irradiation was revealed.
Characteristic neurophysiological changes of the acutely prenatally irradiated children are also
etiologically heterogeneous, but the dose-effect relationship, especially at critical periods of cerebrogenesis,
testifies the impact of prenatal irradiation.
This study suggests that prenatal exposure to ionising radiation at thyroid foetal dose 0.2–2 Gy andfoetal dose 11–92 mSv can result in detectable brain damage.
The data obtained reflect great importance, interdisciplinarity, and complexity of such problem as brain
damage in utero following radioecological disaster and a necessity to integrate international efforts to its
solving.
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