Activitas Nervosa Superior Rediviva Volume 51 No. 1-2 2009

ORIGINAL ARTICLE

The brain bioelectric activity of the Belarusian persons
irradiated in utero as a result of Chernobyl accident
Sergey Igumnov
Belarusian Medical University, Minsk, the Republic of Belarus.
Correspondence to: Prof. Dr. S. Igumnov, Belarusian Medical University, 83, Dzerzhinski ave., Minsk 220116,
Belarus. phone/fax: +375 17 272 61 97; e-mail: Igumnov.S@tut.by; Sergey_Igumnov@tut.by
Submitted: 2008-11-19
Key words:

Accepted: 2009-01-09

children; irradiated prenatal brain; EEG formation; dominant amplitude and activity;
cerebral assymetry

Act Nerv Super Rediviva 2009; 51(1-2): 55–60 		

Abstract

PII: ANSR51129A03 	© 2009 Act Nerv Super Rediviva

OBJECTIVE : The study examined the formation of bioelectric activity (BEA) of the brain of
250 children at the age of 6–7, 10–12 and 15–16 years from regions highly contaminated by
Chernobyl fallout, who were irradiated in the prenatal period at the time of the Chernobyl
accident in 1986. These children were compared with a control group of 250 childrenof the same age from non-contaminated areas of Belarus. METHODS : The examination
included visual and computerized analysis of EEG as well as psychiatric examination andassessment of intellectual level. RESULTS: In the both groups of children at the age of 6–7
the dominant were the variants of age norms (46.4% vs 44.8%; p=0.592) and synchronized(borderline) EEG (26.4% vs 28.0%; P=0.763). Quite noticeable was the relevant frequencyof the slow type of EEG (19.2% vs 18.4%; p=0.820) as well as paroxysmal activity (8.0% vs
8.8%; p=0.830) in the both groups. At the age of 15–16 in the both groups we registered
relevant decrease of index of θ- and δ-activity. The slow type of EEG in most cases wastransformed into the age norm and synchronized type of EEG. The correlation analysis
showed that the intellectual level of children (IQ) estimated by Wechsler Intelligence Scale(WISC-III) was in the direct proportion to spectral power of α-diapason in frontal lobesof the brain (r=0.38 in the both groups). Mental deficiency of children of the both groups
was accompanied by the decreased level of the coherency of α-diapason. When comparing
the results of BEA research with the dosimetric data we found no relevant correlation ofthese indices. The children with different EEG types did not demonstrate any relevant
differences of medium doses of antenatal exposure. CONCLUSIONS: The revealed changes of
BEA of the brain show distinct age dependency. Their frequency in the cohort of persons
exposed to antenatal irradiation did not have relevant differences from that in control
group.

Introduction

Materials and Methods

The study examined the formation of bioelectric activity (BEA) of the brain of 250 children at the age of 6–7,
10–12 and 15–16 years from regions highly contaminated by Chernobyl fallout, who were irradiated in theprenatal period at the time of the Chernobyl accident
in 1986. These children were compared with a control
group of 250 children of the same age from non-contaminated areas of Belarus.

Participants. The exposed group consisted of 250
persons, born between May 1986 and February 1987
randomly selected from the State Registry cohort ofchildren exposed to radiation in utero following theChernobyl accident. During the Chernobyl accident
their pregnant mothers lived in the highly contaminated settlements with 137Cs soil deposition densities ranged up to 18500 kBq⋅m–2. The control group
Act Nerv Super Rediviva 2009; 51(1-2): 55–60

55

S. Igumnov
Table 1. Age and gender distributions of persons of exposed andcontrol groups
Number of persons inGestation
exposedgroup
control groupperiod,
weeks
M
F
Total
M
F
Total
0-7

35

24

59

38

32

70

8-15

29

24

53

28

24

52

16-25

29

27

56

30

28

58

> 25

33

49

82

32

38

70

Total

126

124

250

128

122

250

consisted of 250 persons born between May 1986 andFebruary 1987, also selected randomly from the State
Registry. Their mothers constantly lived in Belarus settlements minimally contaminated with 137Cs soil deposition densities ranging from 2 up to 200 kBq⋅m–2.
Estimation of the period of gestation at the time of
the Chernobyl accident was based upon the inferredfirst day of the last menstrual period and has been calculated with the modified formula of Schull et al. (1988).
The mean duration of gestation was assumed as 280
days. The day of birth was obtained by interview withthe mothers of the persons. To obtain the age after fertilization, 14 days have been subtracted from the termof gestation at the time of the Chernobyl accident. The
gestational and demographic details for the exposedand control groups are shown in Table 1. There wereno statistically significant differences in gender or gestational period between exposed and control groups.
Methods. The electroencephalographic examination
was conducted in the screened study-room of the functional diagnostics of the Republican Clinic of Radiation
Medicine on the 8-channel electroencephalograph of
the Japanese firm “Nihon Kohden”, the model EEG7314 B/P/F in the first half of the day when the patient
was awake. The registration of the EEG was performed
with the help of bridge electrodes (Ag-Ag-CL), appliedby lithium gel. Biopotentials of the brain were drawn
from 8 symmetric areas of brain after a detailed instructive work and the adaptation of the patients tested tothe conditions of the examination. The constant index
of time was set as 0.3; filters – 75 Hz. EEG signals wererecorded on paper with the speed of 15 mm/s-1, when 1
sm. of amplitude corresponded to 50 mkB. Monopolar
and bipolar diversions of the scheme were used in orderto record the bioelectrical activity of occipital, occipital,
central, frontal, front-temple and back-temple areas of
the right and left cerebral hemisphere.
In parallel with the registration of background EEG(monopolar and bipolar diversions) EEG was recorded
during the application of functional loading (threeminute ventilation, rhythmic photo stimulation with theuse of low, medium and high diapasons of frequency oflight flashes, the test with opening and closing eyes withthe registration of the period of consequences during

56

2–3 minutes after the influence of irritants). The visual
analysis of amplitude-frequency characteristics of the
major rhythm was conducted: α-rhythm, β-potentials,
and slow waves in accordance with the age characteristics of EEG for juveniles. Besides, the pathological formsof activity were registered in the form of the increased
number of steep waves, paroxysmal activity and epicomplexes. During and after the hyperventilation loading we paid attention to the paroxysmal activity and its
concentration around the areas and sides of the brain,
as well as revealed sporadic complexes “steep waveslow wave” (epi-complexes). During the conduction ofphoto stimulation we determined the presence of thephenomenon of the perception of the rhythm of light
flashes and pathological forms of bioelectrical activity
during and after this functional loading (paroxysmal
activity, steep waves, “epi-complexes” etc.), the time ofconsequences of the loading.
We also conducted the computer analysis of EEG
with the help of the complex “MBN-neurocartograph”(Russia). The computer analysis included frequencyamplitude transformation with the spectra of capacity
α-rhythm (8–13 Hz) and the analysis of average frequency of spectrum 0.5–40 Hz. The period of the spectrum analysis was 60 s, the frequency diapason – 1–32
Hz. In all the EEG recordings the artifact fragments were
eliminated before the analysis. The spectrum analysis
was conducted with the application of the method of
Fast Fourier Transformation. The subject of the analysis
included the indices of absolute spectrum power anddominant frequency for the whole diapason of frequencies (1–32 Hz), as well as dominant frequency, absoluteand relative (in % to the whole spectrum contents)
spectrum power around the major frequency diapasons: delta (1–3 Hs), theta (4–7 Hs), alpha (8–13 Hs)
and beta (>13–32 Hs). We also conducted the coherent
analysis: the study of the stability of phase correlations
between symmetric areas.
The results obtained were compared to the age normsof EEG (Loganovskaya & Loganovsky 1977; Niedermeyer & Lopes da Silva 1999). The description of the
major types of EEG was conducted on the basis of the“Terminology Reference Book” which was worked out
by the Committee on Terminology of the International
Federation of the Societies of Electroencephalography
and Clinical Neurophysiology (1978).
The undertaken prospective research of the processof the formation of bioelectrical activity of the brain
within the two groups of children (250 persons) – thechildren exposed to antenatal radiation as a result ofChernobyl accident and the children of the control(unexposed) group allows to approach the solution of
three parallel tasks.
The first, one is the definition of the criteria of theage norm, which is understood as the optimal for thisage level of the development of cerebral structures andneurophysiological mechanisms of adaptation, reflectedin the character of bioelectrical activity.
Copyright © 2009 Activitas Nervosa Superior Rediviva ISSN 1337-933X

The brain bioelectric activity of the Belarusian persons irradiated in utero as a result of Chernobyl accident

The second, one is a comparative analysis of thecharacteristic features and rates of maturity of bioelectrical activity of the brain of persons, exposed to radiation in utero, in different diapasons of doses and theirunexposed peers.
The third task is to reveal the features of the functional state of the brain of the persons with different
levels of intellectual development.
In accordance with the recommendations of a numberof leading neurophysiologists (Loganovskaya &Loganovsky 1977) we distinguished the following variants of borderline and pathological EEG changes of thechildren/adolescents at the age from 6 to 16.

■■ epileptic-like activity coming in the form oflong (30 sec and more) bilateral and synchronic
generalized paroxysmal peaks.
The juvenile age is characterized by the following typesof EEG:
1. Alpha-type, organized in time and space, which ischaracterized by stable α-rhythm, which spreads over
all the areas of the cortex;
2. Hypersynchronic (synchronized) type;
3. Disorganized alpha-type (α-rhythm, which achieves
50–60 mcV in occipital areas, getting lower in occipital, central, and frontal areas);

1. The borderline (synchronized) θ-type of EEG includes 2 variants of changes in the bioelectrical activity of brain■■ α-synchronized EEG with the domination ofhigh-amplitude (more than 120 mcV), slightly
sharpened, regular in form and amplitude
α-rhythm with lower regional differences and thereaction to afferent irritants;■■ polymorph and synchronized EEG which
is characterized by the combination of thedominant high-amplitude (higher than 120 mcV)
α- and θ-vibration with β-waves of higher (morethan 20 mcV) amplitude. The regional differenceswere smoothed, the reaction to functional loading
was weak.

4. The disorganized type with the predominance of slow
forms of activity was characterized by alpha-activity
in occipital areas of brain, central areas are distinguished by the polymorph curve, in which indistinct
α-rhythm or µ-rhythm was combined with low-amplitude slow waves;

2. In the slow type of EEG the dominant activity was thehigh-amplitude (60–120 mcV) δ- and θ-activity withthe frequency of 3–7 vibrations per sec., which was
registered in the groups of irregular in form and amplitude α-waves, rare β-vibrations, steep waves. The
regional differences were not recorded. The functional loading emphasized the pathological process.

Types of BEA of brain of 6–7 year old children of the
major and control groups are presented in Table 2. As
it follows from the table, both groups are characterized
by the domination of variants of age norm and synchronized (borderline) EEG. It is important to note thesignificant frequency of EEG with the predominance ofslow wave vibration (θ- and δ-vibration), as well as paroxysmal (epileptic-like) activity in both groups, whichreflects the specific features of the formation of bioelectrical activity of brain at the age of 6–7 and corresponds
to the existing data (Loganovskaya & Loganovsky
1977).
The main forms of BEA of brain of the children of
the major and control groups at the age of 10–12 areshown in Table 3. We have not noticed any relevant differences in frequency of separate types of EEG in the
exposed and control groups of children.
The main forms of BEA of the brain in the exposedand control groups at the age of 15–16 are shown in
Table 4. We have not noticed any relevant differencesin frequency of separate types of EEG in the in the
exposed and control groups of persons.
The data obtained as a result of the prospective studyof the process of the maturity of BEG of the brain of thechildren from the major and the control groups allow
us to make a conclusion that the maturity of brain of
the children/adolescents from 6 to 15–16 is character-3. The EEG with paroxysmal (epileptic-like) activity was characterized by distinct disorganization ofcrust rhythm. On the background of the polyrhythmic curve we registered the complexes of “steep-slowwave”, “the peak-wave”, which were both of a diffuse
character (appeared in all the areas of brain) and concentrated in one of the diversions, coming as generalized bilateral and synchronized paroxysmal chargesof vibrations which were abnormal in form and frequency (the duration of paroxysm is not less than 5sec).
In reference to space distribution of pathological paroxysmal (epileptic-like) activity we distinguish 3 groups:■■ diffuse epileptic-like activity;■■ epileptic-like activity having distinct
predominance in one of the areas of brain (nodal
epileptic-like activity);
Act Nerv Super Rediviva Vol. 51 No. 1-2 2009

5. Desynchronized type, which was first formed at thejuvenile age on the background of polymorph-synchronized and slow type of EEG, was characterized
by the substitute of wave activity, slow and regular intime, by faster and less regular vibrations of biopotentials of smaller amplitude.

Results57

S. Igumnov
Table 2. The types of bioelectrical activity of brain of the children from the exposed and control groups at the age of 6-7.
Types of bioelectrical activity of brain

Exposed group(n=250)n%Control group(n=250)n%

The reliability of the
distinctions
χ2Р

Normal EEG

116

46,4

112

44,8

0,288

0,592

Synchronized Type, including:

66

26,4

70

28,0

0,091

0,763

-α-synchronized EEG

19

7,6

21

8,4

0,109

0,741

-polymorph and synchronized EEG

47

18,8

49

19,6

0,013

0,909

Slow type

48

19,2

46

18,4

0,052

0,820

EEG with epileptic-like activity

20

8,0

22

8,8

0,046

0,830

Table 3. Main types of bioelectrical activity of brain of the children from the exposed and control groups at the age of 10-12.
Types of bioelectrical activity of brain

Exposed group(n=250)Control group(n=250)

N

%

N

%

The reliability of the
distinctions
χ2Р

Normal EEG

136

54,4

131

52,8

0,129

0,719

Synchronized type, including:

72

28,8

86

34,4

1,814

0,178

-α-synchronized EEG

51

20,4

59

23,6

0,746

0,388

-polymorph and synchronized EEG

21

8,4

27

10,8

0,830

0,362

Slow type

29

11,6

18

7,2

2,845

0,092

EEG with epileptic-like activity

13

5,2

15

6,0

0,151

0,698

Table 4. Main types of bioelectrical activity of brain of persons from the exposed and control groups at the age of 15-16.
Types of bioelectrical activity of brain

Exposed group(n=250)
N

%

N

%

χ2

Р

Normal EEG

121

49.8

111

44.4

1.439

> 0.2

Synchronized type

47

19.3

52

20.8

0.163

> 0.5

Desynchronized α-type

32

13.2

33

13.2

0.0001> 0.9

Disorganized type with predominance of slow formsof activity

18

7.4

23

9.2

0.519

> 0.3

Desynchronized type

25

10.3

31

12.4

0.546

> 0.3

ized by the increasing domination of regular in form
an amplitude α-rhythm, the increase in its index, frequency and the decrease in amplitude (from 60–70
mcV to 40–50 mcV) (Igumnov & Drozdovitch 2002).
We recorded the relevant decrease in distinction andfrequency of slow wave θ- and δ-activity in both groups.
The slow type of EEG in most cases was transformed
into EEG with a slight disorganization of cortex rhythm(the variant of age norm) or the synchronized type of
EEG.
The structure of the synchronized type of EEG wascharacterized by a relevant increase in frequency of
α-synchronized EEG (p<0.01) and a relevant decreasein frequency of EEG of the polymorph-synchronizedtype (p<0.01).

58

Control group(n=250)

The reliability of the
distinctions

At the juvenile age the EEG showed polyphase vibration; the degree of the distinction of low amplitude slow
vibration in the central parts of the cortex decreased. By
the age of 15–16 α-rhythm was distinct in the occipitalpart of the cortex in 75 % of cases and dominant in 46%
of cases in the central parts of the cortex. A large degreeof similarity between α-rhythm of occipital, occipitaland central, frontal parts was recorded.
At the age of 15–16 the reaction to the hyperventilation became less distinct. At the same time we recorded
the change in the character of reaction. The reactionin the form of slow vibration in the occipital parts disappeared, while in the frontal parts of the crust it was
dominant in the form of generalized slow waves and
Copyright © 2009 Activitas Nervosa Superior Rediviva ISSN 1337-933X

The brain bioelectric activity of the Belarusian persons irradiated in utero as a result of Chernobyl accident

hyper synchronized slow vibration in the front parts ofcortex.
The age dynamics of the BEA of brain was also characterized by the gradual fading of short-term flashes(less than 5 sec.) of bilateral and synchronized paroxysmal slow activity (recorded at the age of 6–7 on the
background of variants of age norm and synchronizedtype of EEG). Healthy children from the major andcontrol groups at the age of 10 and up did not demonstrate these EEG-phenomena.
At the same time, more stable in the process of age
dynamics of EEG of brain were the cases of paroxysmal (epileptic-like) activity, which was combined withspeech retardation, motor and study skills, the syndrome of the deficit of attention combined with hyper
activity, somatic and motor vegetative dysfunction.
The visual analysis of EEG at the age of 6–7 revealeda distinct cerebral hemispheres asymmetry among40 (16.0%) of children from the major group and 35(14.0%) children from the control group.
According to the data published and our observation healthy children demonstrate a normal cerebral
hemisphere asymmetry, which is represented in theinsignificant reduction (the decrease in amplitude) of
the major rhythm over the dominant hemisphere (leftfor right-handed people) with a slight predominance ofslow θ-activity in frontal sections of this hemisphere.
The asymmetry index in these cases does not exceed
5%.
The predominance of pathological activity in theright hemisphere was revealed in 4 cases (1.6%) among
the children from the exposed and 3 (1.2%) of the children from the control group and was characterized by
the predominance of the slow wave activity in it (mainly
in frontal-occipital-temporal part).
Left-hand cerebral hemisphere asymmetry wasrecorded among 6 tested children (2.4%) in the exposedand 3 (1.2%) in the control group. It was characterized
by a distinct (more than 5%) reduction of the exposed
α-rhythm and the displacement of pathological vibration into the left hemisphere (mainly in frontal-temporal part).
We also revealed an intermediate type of asymmetry,
which was characterized by the predominance of theslow wave activity in frontal-temple part of one hemisphere and occipital-temporal part of the other hemisphere (30 cases – 12.0% in the exposed group and 29(11.6%) – in the control group; p>0.2).
In the course of investigation we have not noticed
any relevant changes in frequency of hemisphere asymmetry and central changes of EEG between the exposedand control groups of children. According to the data of
the prospective analysis the children of all the gestation
ages were characterized by the general tendencies of thematurity of BEA of brain.
While comparing the results of the neurophysiologic
analysis with the dosimeter data we revealed the absenceof relevant correlation between these indices. The chilAct Nerv Super Rediviva Vol. 51 No. 1-2 2009

Table 5. Dosimeter indices among the children from the exposedgroup at the age of 6-7 with different types of BEA of brain.
The number ofchildren

The dose ofantenatal exposure
to thyroid, Gy

Normal EEG

116

0,27 ± 0,36 *Synchronized type66

0,45 ± 0,68

Slow type48

0,40 ± 0,58

EEG with epileptic-like
activity

20

0,47 ± 0,63

Total

250

0,39 ± 0,55

Types of bioelectricalactivity of brain* Mean ± standard deviation
Table 6. Dosimeter indices among the children from the exposedgroup at the age of 10–12 with different types of BEA of brain.
The number ofchildren

The dose ofantenatal exposure
to thyroid, Gy

Variants of the age
norm

136

0,33 ± 0,45*

Synchronized type,including:72

0,46 ± 0,67

Slow type29

0,42 ± 0,38

EEG with epileptic-like
activity

13

0,43 ± 0,69

Total

250

0,39 ± 0,55

Types of bioelectricalactivity of brain* Mean ± standard deviation
Table 7. Dosimeter indices among the persons from the exposedgroup at the age of 15–16 with different types of BEA of brain.
The number ofchildren

The dose ofantenatal exposure
to thyroid, Gy

Normal EEG

1210.34 ± 0.49

Synchronized type47

0.39 ± 0.49

Desynchronized α-type

32

0.49 ± 0.49

Disorganized type withpredominance of slow
forms of activity

180.70 ± 1.19

Desynchronized type25

0.32 ± 0.34

Total

250

0,39 ± 0,55

Types of bioelectricalactivity of brain* Mean ± standard deviation

dren with different types of BEA of brain did not show
any relevant differences between average doses of antenatal exposure of thyroid to radiation (Tables 5–7).
The correlation analysis shows that the level ofintellectual development of children, assessed by
Wechsler Intelligence Scale for Children (WISCIII-UK), is directly proportional to the spectral power59

S. Igumnovof α-diapason in frontal areas of brain (r= 0.38 in bothgroups). Lower intellect, the development of emotionaland behavioral disorders among the children of bothgroups were accompanied by the lower level of coherence in α-diapason, especially in frontal areas of brain.

Discussion
The data obtained as a result of the 10-year prospective
study of the process of maturity of bioelectrical activityof brain of the children from the major and the control
groups allow us to make the conclusion that the maturityof BEA of brain of the children from 6 to 15–16 years
old is characterized by the increased domination of theregular in form and amplitude α-rhythm, the increaseof its index, frequency and the decrease of amplitude(from 60–70 mcV to 40–50 mcV).
Both groups showed valid decrease of distinction
and frequency of slow-wave θ- and δ-activity. The slow
type of EEG in most cases was transformed into the
EEG with a slight disorganization of cortex rhythm (thevariant of age group) or the synchronized type of EEG.
While comparing the results of neurophysiological research with the dosimetric data we revealed theabsence of relevant correlation between these indices.
People with different types of BEA of brain did not have
any relevant differences in average doses of antenatal
exposure of thyroid to radioisotopes.

60

Conclusions
The research undertaken allows us to make a conclusion that the changes noticed in bioelectrical activityof brain show obvious age correlation; their frequency
among the persons, exposed to antenatal radiation,
does not radically differ from that of the persons fromthe control group.
REFERENCES
1 Igumnov SA & Drozdovitch VV (2002). Antenatal exposure: Neuropsychiatric Aspects. Moscow: RADECON, 208 pp.
2 Loganovskaya T & Loganovsky K (1977). Brain laterality and psychopathology in children irradiated in utero. In: Abstracts of 4th
Laterality and Psychopathology Conference, June 19−21,1997,
London, P.34.
3 Niedermeyer E & Lopes da Silva E (1999). Electroencephalography. Basic Principles, Clinical Applications and Related Fields.
− Baltimore–Munchen.
4 Schull W, Otake M, Yoshimaru H (1988). Effect on intelligence testscore of prenatal exposure to ionizing radiation in Hiroshima
and Nagasaki: A comparison of the T65DR and DS86 dosimetry
systems. In: Technical report RERF TR 3−88.

Copyright © 2009 Activitas Nervosa Superior Rediviva ISSN 1337-933X