Edward C. Beck

The effects of maturation and aging on the wave form of visually evoked potentials

Abstract Visually evoked responses (VERs) of 215 normal subjects, aged 1 month–81 years, were studied with the following results. Amplitudes of several waves in the first 250 msec of the VER changed markedly with age. In responses recorded from the occiput there was a rapid increase in amplitude reaching a maximum in 5–6-year-old children. The mean amplitude of VERs at this age was about twice as large as in some older age groups. With children of 7 years and older there was a decline in amplitude until ages 13–14, when an abrupt increase in amplitude appeared. Amplitude appeared to stabilize at about age 16. With older subjects, mean age 67 years, earlier components, those appearing in the first 100 msec, were consistently larger and arrived significantly later. With infants, mean age 3 years, later components, those after 100 msec, had significantly longer peak delays. A comparison of responses from different brain areas as well as the degree of homogeneity of VERs at different age levels showed a gradually changing relationship with increasing age.

Phase of alpha brain waves, reaction time and visually evoked potentials

Abstract A reaction time study was conducted in which twenty subjects were asked to respond to single flashes of light by closing a response switch as quickly as possible. The flashes were presented during six different phase intervals of alpha waves to determine whether reaction times would be related to alpha phase, thus reflecting changes in cortical excitability. Reaction times were found to be reliably faster when the stimulus light was flashed during certain portions of the alpha wave, thus supporting the hypothesis of an excitability cycle being related to the alpha wave. Inked plots of the resulting averaged visually evoked potentials yielded a complex wave consisting of eight distinct components in the first 300 msec of the response. Only two of these components correlated positively and significantly with reaction time. The peak delay of the earliest and most highly correlated of the two components was used as a measure for the interval of time required for the volley initiated by the flash to have reached the cortex and the neural integration necessary for “perception” to have occurred. When the alpha phase during which the light was flashed was corrected by this amount (57 msec), fastest mean reaction times were found to fall on a surface negative phase of the wave while the slowest fell on a positive phase.

The visual evoked response: A comparison of bright and dull children ☆

Abstract Visual evoked responses were recorded from central and occipital scalp of twenty bright children (Full Scale WISC scores ranging from 120 to 140, X = 130 ) and twenty dull children (Full Scale WISC scores ranging from 70 to 90, X = 79 ). All subjects were 10 or 11 years old and each group was composed of ten boys and ten girls. Results were: (1) The late components (100–250 msec) of responses recorded from both occipital and central scalp were reliably larger for the bright children. (2) Dull children demonstrated essentially no hemispheric differences between the amplitudes of the right and left central responses. The bright subjects had right central responses which were consistently larger than responses from the late components of the left scalp. This finding was consistent at several stimulus intensities. Differences between the bright and dull children did not appear to be simply a function of the maturational process. The bright childrens VER amplitudes were similar to normal 13- and 14-year-old childrens; however, the dull childrens VER amplitudes were smaller than those of either younger children or normal children their own age.

The effects of alcohol on visual and somato-sensory evoked responses

Abstract Nine subjects, all moderate drinkers, imbibed various amounts of alcohol or a placebo, after which visual and somato-sensory evoked responses were recorded. The 95% alcohol doses were 0.41 g and 1.23 g/kg of body weight, the equivalent of 1 and 3 ounces of alcohol, respectively, for a 160 pound man. After ingestion of 3 ounces of alcohol the amplitude of a number of a late waves of both visual and somatosensory evoked responses recorded from central areas was attenuated significantly. Evoked responses recorded from the occipital area showed no such changes. With some subjects, a hemispheric asymmetry of amplitude, generally noted with recordings from central areas, disappeared after alcohol ingestion.

Visual and somato-sensory evoked responses from mongoloid and normal children

Abstract Visual and somato-sensory evoked responses were recorded from central and occipital scalp of twenty-four mongoloid and twenty-four normal children matched for age, handedness and sex. Experiments were designed to measure both response reliability and group homogeneity. A factorial design was used to assess differences in latency of wave components and peak-to-through amplitude. The results were as follows. 1. 1. Visual and somato-sensory evoked response measures of reliability were high for both mongoloid and control groups. There were no significant differences between groups in either short- or long-term reliability measures. 2. 2. The amplitude of visual evoked responses recorded from central scalp was greater in the right hemisphere with the control group, while no significant hemispheric asymmetry was demonstrated in the responses of the mongoloid group. 3. 3. The visual evoked responses recorded from occipital scalp and the somato-sensory responses recorded from central scalp were more homogeneous among the mongoloid subjects than were the responses of the control group. The somato-sensory response of the mongoloid children was sufficiently unique to be recognized with relatively casual inspection. 4. 4. Markedly greater amplitudes and later peak latencies were found in the late components of the pattern in mongoloid children. Large amplitude differences distinguished the two groups regardless of shock intensity level. Mongoloid subjects give highly stable and more homogeneous evoked responses to flash and shock stimuli than control subjects. Although their evoked response does not “fit” those in other studies of impaired CNS variables, it is proposed that the mongoloid group includes a unique CNS disorder that is common only to the subjects in the group and that this disorder results in a stable and characteristic response.

Visually Evoked Potentials: Amplitude Changes with Age

Visually evoked potentials of 215 subjects, aged 1 month to 81 years, were studied. Amplitudes of waves in the first 250 milliseconds of the response changed markedly with age. In responses recorded from the occiput, there was a rapid increase in amplitude reaching a maximum in the 5- to 6-year-old group, with means of amplitudes at this age being about twice as large as means of some older age groups. With children 7 years and older there was a rapid decline in amplitude until ages 13 to 14, when an abrupt increase in amplitude appeared. Amplitude appeared to stabilize at about age 16. In older subjects, mean age 60 and beyond, significant changes were noted in the earlier components of the response.

The visually evoked potential in twins

Abstract Visually evoked responses were studied in monozygotic and dizygotic twins, triplets and unrelated children age-matched with the monozygotic twins. Scalp leads from occipital and central areas carried EEG activity to an electronic computer (CAT) which was set to sum evoked responses, following 100 flashes of light. The degree of similarity between pairs of evoked response wave patterns were determined by Pearson product-moment correlations for two analysis times, 250 and 400 msec. Intra-twin correlations of the identical twins were significantly higher than those of the other groups. Correlations of non-identical twins and non-twins matched for age were not significantly different. The first 250 msec of the evoked responses recorded from the occipital area consistently yielded the highest correlations. In a number of instances an identical twins visually evoked response was more like that of his twin sib than like another of his own recorded at a different time.

Long-Term Stability of Visually Evoked Potentials in Man

Although the variability of averaged evoked potentials as recorded from cortex in man has been a constant source of concern among investigators, the degree of variability has not received systematic treatment. The authors have accordingly undertaken an exploratory study of reliable differences that may occur in the first 300 msec of the averaged evoked response over long periods of time. Computer analysis of visually evoked responses in seven subjects over several weeks indicated stability of the response of each individual, with reliable intra-individual correlations. Inter-individual differences, however, were large. The evoked responses of different individuals were found to be unique.

Evoked response similarity in monozygotic, dizygotic and unrelated individuals: A comparative study ☆

Abstract Visual, auditory and somatosensory evoked responses were recorded from forty-four sets of monozygotic (MZ) twins, forty-six sets of dizygotic (DZ) twins, and forty-six pairs of unrelated, age-matched individuals (UR). Two methods were utilized to compare the similarity between pairs of responses. For the wave form comparison, digitized portions of two responses were correlated to determine the degree of similarity between responses. The second method of analysis was an amplitude comparison which determined the amount of voltage change occurring over several time epochs of the evoked response. Each epoch analyzed contained a major peak and trough of the response. The most prominent finding of the study was that the evoked responses of MZ pairs exhibited a consistently higher degree of similarity than those of the DZ or UR groups. In general, this relationship was found for all three sense modalities tested, regardless of scalp area recorded from or the method used to determine similarity between responses. Thus, our results indicated a considerable hereditary component in the wave characteristics of visual, auditory and somatosensory evoked responses.

Visual and somatosensory evoked potential characteristics of patients undergoing hemodialysis and kidney transplantation

The effects of prolonged hemodialysis and kidney transplantation on visual and somatosensory evoked potentials and EEG frequency were assessed. Significant changes were found in both amplitude and latency characteristics of evoked potentials recorded from eight hemodialysis patients. Their evoked potentials tended to be of longer latency and larger amplitude when compared to responses of an age-matched control group. This was true for visual and somatosensory responses recorded from several scalp locations. A correlational analysis revealed no consistent relationship between blood chemistries and evoked potential characteristics. EEG power spectral analysis showed that the dominant frequency of five of the eight dialysis patients was in the 8-10 c/sec range. Two other patients demonstrated EEG frequencies which were scattered across the 3-12 c/sec range while for another subject the dominant frequency was 7-8 c/sec. The evoked potential latencies and amplitudes of patients with successful kidney transplant tended to return to the normal range and their predominant EEG frequency increased to around 10 c/sec. A depression of function in those neural systems underlying the visual and somatosensory modalities, along with a reduction in the cortical suppression of afferent stimulation normally exerted by the thalamic reticular system and the basal ganglia were postulated to account for the reported findings.