the study was conducted in neurophysiology division of defence institute of physiology & allied sciences ( dipas ) , delhi , from april to july 2010 . ten healthy young male volunteers ( 21 - 30 yr ) with average education level of viii - x standard of the indian education system ( 10 yr of total education ) drawn randomly from the indian army participated in the study . they were free from any neurological disorder especially hearing loss , sleep - related and cardiac problems and diabetes . they were not taking any sort of psychotropic , psychoactive or other drugs during the course of the study and were abstained from alcohol and smoking during the experiment . the purpose of the study was explained to them and written informed consent was obtained . study design : the study was divided into two phases : pre- and post - intervention . a complete set of parameters comprising erp p300 , cnv , mlr and raven 's advanced progressive matrices ( rapm ) were recorded at a fixed time in the morning ( 0700 - 0800 h ) except 36 h sd ( 1900 - 2000 h ) . the first night was adaptation to make the subject comfortable to sleep with the necessary attachments . the first recording ( baseline , bl ) was performed on the morning before the same night sd , the second recording on the morning after one night 's sd ( 24 h sd ) , third recording after 36 h sd ( 36 h sd ) . a 36 h total sd was obtained by keeping the subject awake for 12 h after 24 h of deprivation . fourth recording was taken after recovery sleep ( rec sd ) ; fifth recording after 60 days of meditation practice , on the morning of 24 h sd ( med+24 h sd ) . sixth recording was performed after 36 h sd ( med+36 h sd ) and seventh recording on the morning after recovery sleep ( med+rec sd ) . each volunteer slept for about 7.5 to 8 h during adaptation and baseline nights and 8.0 to 9.0 h during recovery night . the participants were allowed to play video games , watch movies , and read books according to their choice as a tool for maintenance of continuous wakefulness24 . during 36 h sd ( daytime ) , subjects were on regular duty schedule without any extra laborious workload . this was done to assure the homogenous work pattern for them through the period of experiment with no irregular activity . actigraphy was performed using an actiwatch ( aw 64 , mini mitter , usa ) to monitor the activity profile throughout the period of experiment . the threshold activity was set such that even a nap could be detected ( actiware v. 5.0 , mini mitter , usa ) . evoked potentials : scalp was gently cleaned with nprep skin prepping gel ( weaver and company , usa ) and ten20 conductive eeg paste was applied to different locations on the scalp according to the internationally accepted 1020 electrode placement system . ag - agcl disc electrodes ( nicolet biomedical , usa ) were used for recording . all the recordings were done with subjects in supine position and eyes open with restricted eye movements . auditory ( sound ) stimulus was given to the left ear by a headphone ( telephonics , usa ) . p300 : electrodes were placed at a1 and a2 ( reference ) , fpz ( common ground ) , cz and pz ( active ) . two different click sounds , one non - target and the other target , were presented to the subject using standard auditory odd - ball paradigm . the subject was asked to count the rare stimuli with attention and concentration , so that he could prompt the number of clicks he had counted at the end of the session . the stimulus characteristics were - intensity : 80 db spl , sensitivity : 100 v , frequency : 2 khz , sweep pattern : gated , sweep rate : 0.9/sec , lff : 1.0 hz and hff : 30.0 hz for non - target and intensity : 80 db spl , sensitivity : 100 v , frequency : 750 hz , sweep pattern : gated , sweep rate : 0.9/sec , lff : 1.0 hz and hff : 30.0 hz target stimuli . after recording , latencies ( msec ) of peaks n1 , p2 , n2 and p300 and amplitudes ( v ) of p200 and p300 were marked . cnv : electrodes were placed at e1 linked with e2 ( eye movement ) , a1 ( reference ) , fpz ( common ground ) , c3 , c4 , cz and fz ( active ) . the subject worn a pair of led goggles ( nicolet biomedical , usa ) and a headphone ( for visual and auditory stimuli respectively ) . the subject was given two stimuli : the first the subject was asked to be alert and to expect a second stimulus to come forth . after 1 sec of s1 , the second  imperative stimulus ( s2 ) was given in the form of trains of visual led flashes and the subject was asked to press a button to stop the flash . one single sweep was 4 sec long , and eight such sweeps were averaged for 1 set of waveforms . the stimulus characteristics were - intensity : 70 db spl , sensitivity : 2 mv , frequency : 1 khz , sweep pattern : gated , sweep rate : 0.1/sec , lff : 0.01 hz and hff : 30.0 hz . after recording , latencies ( msec ) mlr : electrodes were placed at a1 and a2 ( reference ) , fpz ( common ground ) and cz ( active ) . the volunteer was instructed to concentrate towards the stimuli coming in a synchronized fashion to his left ear . the stimulus characteristics were : intensity : 75 db spl , sensitivity : 100 v , frequency : 500 hz , sweep pattern : gated , sweep rate : 39.1/sec , lff : 10.0 hz and hff : 100.0 hz . latencies ( msec ) of peaks na and pa and amplitude ( v ) of na - pa were marked . subjects were explained the modality of the test in detail and asked to practice with set - i accordingly . each problem page ( in both sets ) contained nine design cells displayed in a square manner of 3 by 3 ( a matrix ) , with the bottom - right cell vacant . the subjects had to predict the possible design pattern for the vacant cell and choose the same from a list of eight patterns provided below the matrix . after completing set - i , they were asked to solve the matrices in the set - ii ( actual test set ) within a time frame of 30 min . the reason for time - locking was to make the subject more attentive towards the test . this was a 25 min session of spiritual exercise performed by moderate workers on a twice daily basis for 60 days . each session consisted of four stages with volunteer sitting in upright position and back erect - first quietly with eyes closed for 6 min . this was followed by the pranayama  udgeet  - the respiratory exercise for the next 6 min , in which the volunteer sat with hands in upright position and mouth shut . the index finger was placed on the forehead ; with next three fingers covering his eyes and the thumb pressing the ear lid . this is to ensure blockage of energy exchange with the universe except through respiration . in this state the person chanted next 6 min the  om was chanted while sitting erect on back and exhaling slowly with the eyes closed . last 6 min were spent in absolute stillness , wherein the volunteer sat with eyes closed and breathing slowly , again in first posture . at the end , participants raised their hand above their head , rasped the palms first slowly , and then briskly , placed the palms over the eyes and the session was completed . statistical analysis : statistical analyses were done using spss 13.0 ( ibm , usa ) . analysis of statistical significance for changes during various conditions was performed using one way anova for repetitive measurements for cnv , p300-erp and mlr . each value at a given condition was compared to that in another condition using multiple comparison ( post hoc ) t - tests . rapm was analyzed using friedman 's rank test for analysis of significant difference within groups , followed by mann whitney 's u test to analyze between group significance . pearson 's product - moment correlation coefficient ( r ) was computed to see for significant correlation between rapm with mlr - na , p300-p3 , p300-p3 amplitude ( amp ) , cnv - m1 , cnv - m1 amp , cnv - m2 and cnv - m2 amp . the determined r was then converted to student 's t - scores for testing of ho ( significance ) . subjects were explained the modality of the test in detail and asked to practice with set - i accordingly . each problem page ( in both sets ) contained nine design cells displayed in a square manner of 3 by 3 ( a matrix ) , with the bottom - right cell vacant . the subjects had to predict the possible design pattern for the vacant cell and choose the same from a list of eight patterns provided below the matrix . there was no time restriction for solving the practice set . after completing set - i , they were asked to solve the matrices in the set - ii ( actual test set ) within a time frame of 30 min . the reason for time - locking was to make the subject more attentive towards the test . this was a 25 min session of spiritual exercise performed by moderate workers on a twice daily basis for 60 days . each session consisted of four stages with volunteer sitting in upright position and back erect - first quietly with eyes closed for 6 min . this was followed by the pranayama  udgeet  - the respiratory exercise for the next 6 min , in which the volunteer sat with hands in upright position and mouth shut . the index finger was placed on the forehead ; with next three fingers covering his eyes and the thumb pressing the ear lid . this is to ensure blockage of energy exchange with the universe except through respiration . in this state the person chanted next 6 min the  om was chanted while sitting erect on back and exhaling slowly with the eyes closed . last 6 min were spent in absolute stillness , wherein the volunteer sat with eyes closed and breathing slowly , again in first posture . at the end , participants raised their hand above their head , rasped the palms first slowly , and then briskly , placed the palms over the eyes and the session was completed . statistical analysis : statistical analyses were done using spss 13.0 ( ibm , usa ) . analysis of statistical significance for changes during various conditions was performed using one way anova for repetitive measurements for cnv , p300-erp and mlr . each value at a given condition was compared to that in another condition using multiple comparison ( post hoc ) t - tests . rapm was analyzed using friedman 's rank test for analysis of significant difference within groups , followed by mann whitney 's u test to analyze between group significance . pearson 's product - moment correlation coefficient ( r ) was computed to see for significant correlation between rapm with mlr - na , p300-p3 , p300-p3 amplitude ( amp ) , cnv - m1 , cnv - m1 amp , cnv - m2 and cnv - m2 amp . the determined r was then converted to student 's t - scores for testing of ho ( significance ) . p300 : n1 , p2 and n2 components of p300 erp did not register any significant change , though there was increase in latencies after 24 and 36 h of sd . latency of p300 registered significant increase after 36 h sd ( table i ) compared to baseline ( p<0.01 ) , and significant reduction was noted after recovery sleep ( p<0.05 ) . amplitude of p300 component increased following 24 h sd as well as 36 h sd ( p<0.01 ) , and returned to its baseline range after recovery sleep ( p<0.01 ) ( table i ) . effect of meditation practice on p300 after sleep deprivation ( sd ) cnv : latencies of n1 and m1 did not alter significantly . however , m2 was delayed significantly after 24 h sd ( p<0.05 ) and the delay was greater after 36 h sd ( p<0.01 ) compared to baseline ( table ii ) . the latency returned to baseline after recovery sleep ( p<0.05 , recovery compared to 36 h sd ) . amplitude of m1 increased after 24 h sd significantly ( p<0.05 ) , which was even higher following 36 h of prolonged deprivation ( p<0.001 ) , compared to baseline . after recovery sleep , there was significant reduction in the amplitude of m1 compared to 36 h sd ( p<0.05 ) . amplitude of m2 showed significant elevation after 36 h sd ( p<0.001 ) compared to baseline . after recovery sleep , significant reduction in amplitude of m2 was observed compared to both 24 h ( p<0.05 ) and 36 h ( p<0.001 ) of sd ( table ii ) . in comparison to baseline , cnv reaction time was prolonged following 24 and 36 h of sd , the latter being significant ( p<0.01 ) . after recovery sleep , reaction time again registered significant decrease compared to 36 h sd ( p<0.01 ) . effect of meditation practice on contingent negative variation after sleep deprivation ( sd ) mlr : latency of the peak na registered no significant change after 24 h sd but significant change following 36 h sd compared to baseline ( p<0.01 ) and recovery ( p<0.05 ) . latency of pa and amplitude of na - pa did not register any significant change at any stage ( table iii ) . effect of meditation on middle latency response after sleep deprivation ( sd ) psychological assessment : total sd decreased number of correct responses in rapm set - ii session after 24 h and 36 h ( p<0.01 ) compared to baseline . this decline was recovered ( p<0.01 , compared to 36 h sd ) after recovery ( fig . ) . number of correct responses in rapm set - ii session showed significant negative correlation with amplitude of m1 component of cnv ( r = -0.66 ; p<0.05 ) at baseline . mlr - na , p300-p3 , p300-p3 amp , cnv - m1 , cnv - m2 and cnv - m2 amp . 1 ) , p300 erp registered no significant changes in terms of latencies of n1 , p2 , n2 and p300 components . cnv : there was no significant change in latencies of n1 , m1 and m2 components of cnv ( table ii ) . amplitude of m1 also did not alter significantly , though there was a significant increase in m2 amplitude after 36 h sd ( p<0.05 ) . mlr : after two months of meditation practice , there was no significant change in any components of mlr ( table iii ) . neuropsychological assessment : total sd slightly decreased number of correct responses in rapm set - ii session after sd compared to baseline ( fig . ) . p300 : n1 , p2 and n2 components of p300 erp did not register any significant change , though there was increase in latencies after 24 and 36 h of sd . latency of p300 registered significant increase after 36 h sd ( table i ) compared to baseline ( p<0.01 ) , and significant reduction was noted after recovery sleep ( p<0.05 ) . amplitude of p300 component increased following 24 h sd as well as 36 h sd ( p<0.01 ) , and returned to its baseline range after recovery sleep ( p<0.01 ) ( table i ) . effect of meditation practice on p300 after sleep deprivation ( sd ) cnv : latencies of n1 and m1 did not alter significantly . however , m2 was delayed significantly after 24 h sd ( p<0.05 ) and the delay was greater after 36 h sd ( p<0.01 ) compared to baseline ( table ii ) . the latency returned to baseline after recovery sleep ( p<0.05 , recovery compared to 36 h sd ) . amplitude of m1 increased after 24 h sd significantly ( p<0.05 ) , which was even higher following 36 h of prolonged deprivation ( p<0.001 ) , compared to baseline . after recovery sleep , there was significant reduction in the amplitude of m1 compared to 36 h sd ( p<0.05 ) . amplitude of m2 showed significant elevation after 36 h sd ( p<0.001 ) compared to baseline . after recovery sleep , significant reduction in amplitude of m2 was observed compared to both 24 h ( p<0.05 ) and 36 h ( p<0.001 ) of sd ( table ii ) . in comparison to baseline , cnv reaction time was prolonged following 24 and 36 h of sd , the latter being significant ( p<0.01 ) . after recovery sleep , reaction time again registered significant decrease compared to 36 h sd ( p<0.01 ) . effect of meditation practice on contingent negative variation after sleep deprivation ( sd ) mlr : latency of the peak na registered no significant change after 24 h sd but significant change following 36 h sd compared to baseline ( p<0.01 ) and recovery ( p<0.05 ) . latency of pa and amplitude of na - pa did not register any significant change at any stage ( table iii ) . effect of meditation on middle latency response after sleep deprivation ( sd ) psychological assessment : total sd decreased number of correct responses in rapm set - ii session after 24 h and 36 h ( p<0.01 ) compared to baseline . this decline was recovered ( p<0.01 , compared to 36 h sd ) after recovery ( fig . ) . number of correct responses in rapm set - ii session showed significant negative correlation with amplitude of m1 component of cnv ( r = -0.66 ; p<0.05 ) at baseline . mlr - na , p300-p3 , p300-p3 amp , cnv - m1 , cnv - m2 and cnv - m2 amp . 1 ) , p300 erp registered no significant changes in terms of latencies of n1 , p2 , n2 and p300 components . cnv : there was no significant change in latencies of n1 , m1 and m2 components of cnv ( table ii ) . amplitude of m1 also did not alter significantly , though there was a significant increase in m2 amplitude after 36 h sd ( p<0.05 ) . mlr : after two months of meditation practice , there was no significant change in any components of mlr ( table iii ) . neuropsychological assessment : total sd slightly decreased number of correct responses in rapm set - ii session after sd compared to baseline ( fig . ) . p300 : n1 , p2 and n2 components of p300 erp did not register any significant change , though there was increase in latencies after 24 and 36 h of sd . latency of p300 registered significant increase after 36 h sd ( table i ) compared to baseline ( p<0.01 ) , and significant reduction was noted after recovery sleep ( p<0.05 ) . amplitude of p300 component increased following 24 h sd as well as 36 h sd ( p<0.01 ) , and returned to its baseline range after recovery sleep ( p<0.01 ) ( table i ) . effect of meditation practice on p300 after sleep deprivation ( sd ) cnv : latencies of n1 and m1 did not alter significantly . however , m2 was delayed significantly after 24 h sd ( p<0.05 ) and the delay was greater after 36 h sd ( p<0.01 ) compared to baseline ( table ii ) . the latency returned to baseline after recovery sleep ( p<0.05 , recovery compared to 36 h sd ) . amplitude of m1 increased after 24 h sd significantly ( p<0.05 ) , which was even higher following 36 h of prolonged deprivation ( p<0.001 ) , compared to baseline . after recovery sleep , there was significant reduction in the amplitude of m1 compared to 36 h sd ( p<0.05 ) . amplitude of m2 showed significant elevation after 36 h sd ( p<0.001 ) compared to baseline . after recovery sleep , significant reduction in amplitude of m2 was observed compared to both 24 h ( p<0.05 ) and 36 h ( p<0.001 ) of sd ( table ii ) . in comparison to baseline , cnv reaction time was prolonged following 24 and 36 h of sd , the latter being significant ( p<0.01 ) . after recovery sleep , reaction time again registered significant decrease compared to 36 h sd ( p<0.01 ) . effect of meditation practice on contingent negative variation after sleep deprivation ( sd ) mlr : latency of the peak na registered no significant change after 24 h sd but significant change following 36 h sd compared to baseline ( p<0.01 ) and recovery ( p<0.05 ) . latency of pa and amplitude of na - pa did not register any significant change at any stage ( table iii ) . effect of meditation on middle latency response after sleep deprivation ( sd ) psychological assessment : total sd decreased number of correct responses in rapm set - ii session after 24 h and 36 h ( p<0.01 ) compared to baseline . this decline was recovered ( p<0.01 , compared to 36 h sd ) after recovery ( fig . ) . number of correct responses in rapm set - ii session showed significant negative correlation with amplitude of m1 component of cnv ( r = -0.66 ; p<0.05 ) at baseline . mlr - na , p300-p3 , p300-p3 amp , cnv - m1 , cnv - m2 and cnv - m2 amp . 1 ) , p300 erp registered no significant changes in terms of latencies of n1 , p2 , n2 and p300 components . cnv : there was no significant change in latencies of n1 , m1 and m2 components of cnv ( table ii ) . amplitude of m1 also did not alter significantly , though there was a significant increase in m2 amplitude after 36 h sd ( p<0.05 ) . mlr : after two months of meditation practice , there was no significant change in any components of mlr ( table iii ) . neuropsychological assessment : total sd slightly decreased number of correct responses in rapm set - ii session after sd compared to baseline ( fig . ) . the present study used a novel approach to evaluate the psychophysiological and functional measures of cognition together . the study also attempted to establish the relationship between the psychophysiological components i.e. rapm scores with the latencies and amplitudes of p300 , cnv and mlr . in our study p300 component of erp showed significant increase after 36 h of sd in terms of latency . this is indicative of reduced ability of concentration , discrimination of a target stimulus in a train of non - target stimuli ; matching the stimulus against the memory representation of the relevant ( target ) stimuli and decision making ( whether the presented stimulus is a target one ) . p300 is elicited when a form of selective attention is required by the subject in order to identify infrequent occurrences of a target ( relevant ) stimulus , which is presented unpredictably24 . the delayed p300 latency also indicates that there is improper classification and recognition of stimulus as relevant to the assigned task . lee et al10 have reported significantly prolonged latency of n2 and decreased amplitudes of n1 , p200 and p300 . in our study delay in latencies of n1 , p2 and n2 components of this erp n2 preceding p300 may directly affect the absolute timing of decision processes in sensory discrimination ; and it is also sensitive to the cognitive attributes to the stimulus27 . amplitude of p300 increased after 24 and 36 h sd , the latter being significant compared to baseline . p300 amplitude depends upon the selective attention of a subject , which is compromised after sd . after sd a person gets inattentive to a considerable extent which results in unpredictable presentation of a predictable stimulus . another possible explanation may be that , stimuli which signal some internal response ( like memory task in p300 ) or provide useful information ( like target and non - target discrimination criterion in p300 ) , result in an erp component ( like p300 ) with definitely higher amplitude24 . cnv appears to represent the summation of at least two , probably more , component waveforms . one previous study has reported increase in amplitude of cnv components after 24 h sd in epileptics28 as found in our study . in our study , the early component of cnv ( m1 ) was delayed non - significantly following sd . m1 is a stimulus related frontally predominant component , perhaps reflecting the orienting response . on the other side , m2 , the late cnv component is a centrally predominant component thought to be related to the premotor potential associated with the motor response29 . a delayed m1 indicates subject 's deficient ability to get  warned after the warning stimulus ( s1 ) and to get oriented about s1 as well ; and delayed m2 indicates improper preparation for the subsequent motor response . latency of m2 was significantly increased following 24 h sd and 36 h sd compared to baseline . a significantly prolonged reaction time implies a state of deficient motor response , subject 's incapability of perceptual processing and preparatory judgment . na is believed to be generated subcortically and pa , bilaterally within the primary auditory cortex30 . after continuous wakefulness , the conduction at the subcortical level may be delayed ; or there may be some changes , which appear to resemble changes in na latency after subcortical lesion . the reversal of the situation after recovery sleep i.e. , reduction of na latency after recovery sleep proposes that , the effect of prolonged wakefulness is ameliorated by 8 - 9 h of recovery sleep . in humans mid latency responses may actually consist of overlapping potentials originating from primary auditory cortex , ascending activating system and/or subcortical structures31 . it is possible that sd may lead to changes in neural processing at some or all of these levels . as mentioned earlier23 , mlr has got some attention related cortical components , which may deteriorate after sd . rapm measures two main components of intelligence ; the ability to think clearly and make sense of complexity known as  eductive ability , and the ability to store and reproduce information called  reproductive ability32 . it appears to measure a type of reasoning ability with very high predictive validities in most occupational groups . it may be posible that 36 h sd interferes with educative and reproductive ability , which leads to deficient problem solving and analytical ability . the educative and reproductive abilities involve important components of cognitive function like attention , vigilance , concentration and working memory . it was therefore , not surprising that a significant negative correlation was obtained between the amplitude of m1 ( early cnv ) and number of correct responses in rapm set - ii . a plausible explanation for this effect is that , following sd , a greater effort in terms of trying to concentrate harder is needed for the same extent of task complexity . the greater amount of subjective effort is reflected in increased m1 amplitude and the poor performance is depicted by reduced rapm scores . in conclusion , the present study validates and extends the value of p300 , cnv and mlr as the markers for quantification of the degree of cognitive impairments after total sd . it also shows that total sd involves deficit in sensory perception as well as inefficiency in motor responses , which leads to cognitive impairment in an integrative manner , as is evident from significant changes in p300 , cnv , mlr and rapm scores . thus , cognitive impairment after total sd is an assembly of dysfunctions in different regions of brain rather than being a single component ; and the event related ( p300 and cnv ) and evoked potentials ( mlr ) can analyze the situation real - time , which is further confirmed by rapm scores , the psychophysiological assessment tool .
background & objectives : decline in cognitive functions is a major challenge for professionals during sustained wakefulness . we used middle latency response ( mlr ) , event related potentials p300-erp and contingent negative variation ( cnv ) and raven 's advanced progressive matrices ( rapm ) - a standard neuropsychological test were used to evaluate cognitive impairment after total sleep deprivation ( sd ) ; and to study the impact of meditation as an intervention for this impairment.methods:healthy male volunteers ( n=10 ) drawn randomly from the indian army participated in a 6-night study design executed before and after two months of meditation practice : night 1adaptation , night 2baseline , night 324 h sd , night 4-recovery sleep , night 524 h sd after 60 days meditation , night 6-recovery sleep after sd . 
 a 36 h sd was obtained by keeping the subject awake for 12 h after 24 h sd.results:the latency and amplitude of p300 increased after 36 h sd . 
 amplitudes and latencies of both early and late cnv increased after 24 and 36 h sd , indicating deficient orientation and impairment of attention and perception . 
 prolonged cnv reaction time after 36 h sd manifested deficient motor response following second ( imperative ) stimulus . 
 latency of mlr na registered significant change following 36 h sd compared to baseline ( p<0.01 ) and recovery ( p<0.05 ) . 
 rapm score showed significant decrease after 36 h of wakefulness indicating impaired analytical ability and difficulty in problem solving . 
 none of these parameters showed any significant alteration after sd , following meditation practice.interpretation & conclusions : the present results showed that sd impaired cognitive performance to graded extents significantly , but this deterioration could be improved to a significant extent using meditation .