Walter W. Surwillo

Cortical evoked potentials in monozygotic twins and unrelated subjects: Comparisons of exogenous and endogenous components

Cortical evoked potentials to auditory stimulation were recorded in six pairs of monozygotic twins and six pairs of unrelated subjects matched for age and sex while they performed a stimulus detection task. The cortical potentials were coherently averaged, and the peak latencies of the exogenous (P1, N1, and P2) and endogenous (N2 and P3) components of the average evoked potential (AEP) were investigated. It was hypothesized that latency of the exogenous components of the AEP would be similar in all matched pairs since the characteristics of these components depend primarily on the physical parameters of the stimulus. As endogenous components appear to be associated with a persons intentions, expectations, and decisions, we expected them to be more alike in twins than in unrelated individuals. Findings were in accord with the hypothesis. Latencies of the exogenous components were closely similar in all pairs of subjects. By contrast, latencies of the endogenous components were significantly (P≤0.001) more alike in twins than in unrelated subjects.

Developmental Changes in the Speed of Information Processing

Summary Speed of information processing was estimated in a group of 108 boys, aged 54–207 months, by subtracting each Ss simple reaction time (RT) from his choice RT obtained in a task involving two alternative stimuli. The resulting quantity, namely the decision time (DT), was found to be related to age according to a reciprocal power-law function. The correlation coefficient between log DT and log age, which was equal to - .69, was highly significant (p < < .001). On the basis of the regression equation derived from these data, 5-year-olds took nearly three times longer than 17-year-olds to process one bit of information.

Relationship between EEG Activation and Reaction Time

The relationship between RT and EEG activation, as defined by measurements of both amplitude and frequency (period) of waves from the dominant hemisphere, was investigated. A 250-c/sec. tone that was presented without a preparatory warning signal was the stimulus. Within-subject correlations from 99 Ss supported the hypothesis of an association between EEG activation and behavioral arousal. Frequency of the waves was a better predictor of RT than amplitude.

Average Evoked Potentials

In the decade of the 1980s, many clinical EEG laboratories have added average evoked potential studies to their routine procedures. Indeed, short-latency brain-stem auditory-evoked potentials, as well as short- and intermediate-latency cortical-evoked potentials, lately have proved to be valuable clinical tools for objectively testing afferent functions in patients with neurological and sensory disorders. This being the case, there is need for the EEG technician to become familiar with evoked-potential methods and to add a variety of new skills to his or her repertoire. At the same time, the person reading and interpreting the records will find it necessary to deal with concepts and techniques that are markedly different from those encountered in EEG interpretation.

The electroencephalogram in the prediction of human reaction time during growth and development

Characteristics of the distributions of electroencephalographic (EEG) half waves recorded in children during performance of a simple auditory reaction time (RT) task were investigated. The purpose was to determine the extent to which difference in these distributions could account for childrens slow RT. The durations of a sample of 760 EEG half waves in each of a group of 41 healthy children aged 5-17 yr were measured and distributed into an interval histogram, and the first four central moments of the 41 distributions were computed. All four of the moments-which measure the central tendency, dispersion, skewness and kurtosis of the distributions-proved to be significantly correlated (p less than 0.01) with RT. The multiple correlation (R) between RT and the four moments was equal to 0.68 and was statistically significant. R was unchanged when only the measures of dispersion, skewness and kurtosis were used as predictor variables, suggesting that the predictive value of the central tendency is low. The predictive capability of a multiple regression equation based on these three predictor variables was tested in an independent group of 42 children also aged 5-17 yr. EEGs and RTs were recorded and this group was treated in exactly the same way as the other group. The correlation between these childrens average RTs and their RTs as estimated from the other groups regression equation was 0.53. These findings suggested that knowing the degree of dispersion, skewness and kurtosis of the childrens EEG distributions reduces from chance by about 28% the error of predicting their RTs.

SLEEP SPINDLES IN THE EEGS OF HYPERACTIVE CHILDREN

Electroencephalograms (EEGs) of 11 boys, aged 3 to 11 yr., who had been diagnosed as Attention Deficit Disorder with Hyperactivity were compared with 11 controls matched for age and sex. The purpose was to determine whether there was any difference between the groups in the number of sleep spindles present during Stage 2 sleep. The EEGs of the subjects studied were typical of those performed in most clinical laboratories, with approximately 8 min. of daytime Stage 2 sleep recorded for each child. Most of the subjects in both groups were given Chloral Hydrate to induce sleep. The number of sleep spindles/sec. in Stage 2 sleep and the time spent in Stage 2 sleep were estimated for each subject, and means were obtained for both groups. Findings showed no statistically significant differences between hyperactive and control groups. The results cast doubt on the significance of sleep spindle activity in assessing hyperactivity or in resolving current theoretical issues relating to hyperactivity.

BRAIN ELECTRICAL ACTIVITY DURING PRAYER

Electroencephalograms (EEGs) were recorded during rest and during prayer in the laboratory from 6 adults aged 24 to 70 yr. belonging to the Protestant faith. The purpose was to discover whether the electrocortical rhythms during prayer are slower than they are during rest as has been reported to be the case in Transcendental Meditation. Findings did not show any evidence of EEG slowing in prayer. Indeed, the opposite result, namely, a speeding-up of the EEG, was observed in the majority of subjects. In one subject the shift from rest to prayer amounted to an average increase in frequency of 1.6 c/sec. Findings were discussed in relation to similar results which have been reported in highly experienced Yoga meditators and advanced Transcendental Meditators capable of deep meditative states. Confirmatory evidence from one subject who was a highly experienced Sufi meditator is also presented.

Choice reaction time and speed of information processing in old age.

Simple and choice RT were investigated in 54 male Ss, aged 34 to 92 yr. Findings suggested that old age is accompanied by a slowing of information processing.

Cortical evoked potentials in Gilles de la Tourette's syndrome—A single case study

Average cortical evoked potentials (AEPs) to auditory stimulation and AEP recovery functions were investigated in a 13-year-old boy suffering from Gilles de la Tourettes syndrome. Data obtained from the patient while on and off haloperidol were compared with data from a group of normal control subjects matched for age and sex. Latencies of the P2 and N2 components of the AEP were noticeably shorter in the Tourettes syndrome patient than in the control group. Recovery from stimulation, as estimated by the cortical evoked potential to the second of two closely spaced stimuli, was faster in the patient than the controls. After the patients treatment with haloperidol, the latencies of the P2 and N2 components of the AEP and the speed of recovery from stimulation appeared to be no different in the patient than in the control subjects. Findings suggested that cortical excitability is higher in the Tourettes syndrome patient, whose AEPs also showed evidence of a maturational advance over the normal subjects.

Interval histograms of period of the electroencephalogram and the reaction time in twins

Measures of central tendency, dispersion, skewness, and kurtosis of interval histograms of half wavelengths in the electroencephalogram (EEG) and performance on an auditory reaction time (RT) task were compared in seven pairs of male monozygotic twins aged 101–134 months and seven pairs of unrelated boys matched to the twins for age. Interval histograms were formed from measurements of 780 half waves taken from EEGs recorded from the left parietal-occipital derivation while subjects performed the RT task. Except in the case of the dispersion of the EEG distributions, theF ratios of within-pair variance in unrelated pairs to within-pair variance in twins were all statistically significant at the 0.05 level of confidence. Statistically significant intraclass correlations of means, medians, and modes of the histograms were found in the group of monozygotic twins but not in the sample of unrelated subjects. Intraclass correlations for dispersion, skewness, and kurtosis of the histograms and for RT were not significantly different from zero in either the twins or unrelated subjects. EEG findings suggested that the basic frequency of the brains rhythmic electrical activity may be genetically determined; RT findings were inconclusive.