William R. Goff

Brain stem auditory, pattern-reversal visual, and short-latency somatosensory evoked potentials: Latencies in relation to age, sex, and brain and body size

To determine standards of normality for auditory, somatosensory and visual evoked potentials commonly used in the assessment of neurological disease, 8 AEP, 1 VEP and 12 SEP components were recorded to stimulation of left and right ears, eyes, and median nerves in 286 normal subjects ranging in age from 4 to 95 years. Peak and interpeak latencies, and left-right differences in latency, were analyzed as a function of age, sex, and estimates of brain and body size. Major features of the results were: (1) Peak latencies of all components showed statistically significant increases in latency with age except that VEP P100 latency decreased significantly between 4 and 19 years and did not change between 20 and 59 years. (2) In adults the peak latencies of all components were significantly later in males than in females. For AEPs and VEPs these differences were explained by sex differences in brain size, and for adult SEPs were explained by sex differences in arm and shoulder dimensions. No significant sex differences in VEP and SEP latencies were seen in children. (3) Most interpeak latencies showed significant differences in relation to age or sex. (4) Age and sex are useful predictors of latency for nearly all peak and interpeak latencies; in addition, height is a useful predictor of SEP peak latencies. (5) Left-right latency differences showed little age-related, and no sex-related, change. The interlaboratory use of these or other normative data was discussed. It was concluded that these AEP and SEP norms can probably be used in other laboratories if stimulating and recording conditions are similar. However, VEP results are difficult to transfer due to the poorly understood effects of variation in stimulus conditions. Some issues regarding the optimal characterization of norms were also discussed.

Developmental and aging changes in somatosensory, auditory and visual evoked potentials

To assess developmental and aging changes in human sensory systems, components of short-latency somatosensory, brain-stem auditory and pattern-reversal visual evoked potentials, thought to originate in specific structures of these systems, were recorded in 286 normal subjects ranging in age from 4 to 95 years. Analysis was primarily restricted to peak and interpeak latencies; visual evoked potential amplitudes were also analyzed. Major results and conclusions are: (1) Developmental changes (that is, decreases in latency attributable to decreased conduction time in younger subjects) were not seen in the median nerve, in brain-stem auditory pathways, or in some portions of visual cortex. Small developmental changes were seen in the somatosensory afferent pathway from the cervical spinal cord to thalamus, and large changes were seen in somatosensory and visual cortex. Cortical developmental changes appeared not to be complete until 17 years of age or later. (2) Aging changes (that is, increases in latency attributable to increased conduction time in older subjects) were observed in the median nerve, cervical spinal cord, brain-stem auditory pathways, and somatosensory and visual cortex. (3) Visual evoked potential amplitudes tended to decrease with age, particularly during development; amplitude and latency effects were dissimilar for most components. (4) Males tended to show larger aging effects than females. (5) The results suggest that age-related changes in human sensory systems are not uniform, but rather are different in specific portions of these systems, different at particular epochs of the life span, and stronger in males than in females.

Auditory evoked potentials during speech perception.

Neural responses evoked by the same binaural speech signal were recorded from ten right-handed subjects during two auditory identification tasks. One task required analysis of acoustic parameters important for making a linguistic distinction, while the other task required analysis of an acoustic parameter which provides no linguistic information at the phoneme level. In the time interval between stimulus onset and the subjects identification responses, evoked potentials from the two tasks were significantly different over the left hemisphere but identical over the right hemisphere. These results indicate that different neural events occur in the left hemisphere during analysis of linguistic versus nonlinguistic parameters of the same acoustic signal.

The scalp topography of human visual evoked potentials

Abstract The topography of all identifiable components of the scalp-recorded visual evoked potential (VEP) to unpatterned centrally-viewed light flashes presented in Maxwellian view to the right eye was determined for all scalp electrode locations of the 10–20 system and for locations at the right eye, mastoids, and posterior neck. Twenty-two components were analyzed. Of these, six were regarded as electroretinographic, one as myogenic, and the rest as neurogenic. Supplementary analysis suggested that VEP components and their topography are similar whether evoked by unpatterned flashes presented in Maxwellian view, by unpatterned stroboscopic flashes, or by patterned, flashes, but not by pattern reversal. Potentials thought to originate in periorbital musculature were evoked by somatosensory and auditory as well as visual stimuli. They were larger in inexperienced than in experienced subjects, were larger to unpredictable than to predictable stimuli, but did not differ whether the subject was in a Maxwellian view apparatus or seated in a comfortable chair. These potentials can distort recordings of presumptive neurogenic components in the same latency range. These data should aid in predicting VEP characteristics and in assessing myogenic contamination of neurogenic activity. Components thought to be analogous in the somatosensory, auditory and visual modalities were discussed.

Cerebral somatosensory responses evoked during sleep in man

Human somatic evoked responses (SERs) were recorded from the scalps of eleven subjects to percutaneous shock stimulation of median nerve during waking, slow wave and REM sleep. Both short- and long-latency SERs vary systematically with stage of sleep: n1. n1. The cortical primary post-synaptic positivity is markedly reduced in REM sleep compared to waking and slow wave sleep; in contrast, this response in cat is reported to be largest during REM. This possibly reflects a species difference between man and cat in cortical responsiveness during REM. n n2. n2. Short-latency (15 msec) “myogenic” evoked responses recorded percutaneously from trapezius muscle at the neck show no change from waking to sleep. Thus they do not appear to be mediated in the same way as monosynaptic or polysynaptic spinal reflexes found by others to be suppressed during REM. n n3. n3. Long-latency SERs seen during waking are essentially absent in the drowsy subject and during REM. As the EEG synchronizes, late activity occurs consisting of two negative-positive sequences which we label 6a and 6b respectively. Component 6a decreases in amplitude with increasing cortical synchronization; it may correspond to waking component 4 but the latency increase is very large. Component 6b appears in stage 2 at a much longer latency than any waking component and increases in amplitude with increasing synchronization. We suggest that it has no waking counterpart but represents the release of neural activity inhibited in waking and REM. SER components 6a and 6b are also evoked by auditory stimulation. Component 6b corresponds to the K complex.

On-line statistical detection of average evoked potentials: Application to evoked response audiometry (ERA)

An objective method of EP detection in averaged EEG epochs is described which is based on the statistical properties of the averaged EEG in the absence of time-locked EP activity. The statistical properties of the subjects averaged background EEG are summarized by making a set of comparisons between two consecutive EEG epochs immediately preceding each stimulus presentation. After every stimulus presentation, a second set of comparisons is made between the post-stimulus EEG epoch and the immediately preceding pre-stimulus EEG epoch. These two sets of comparisons are then examined to determine whether the latter differ significantly from the former. The technique has been programmed for on-line use on a 12-bit minicomputer, validated on cooperative adult subjects and used for ERA threshold determinations in young children. Using response detection criteria yielding an empirically determined false positive error rate of between 1 and 4%, threshold estimates averaged about 10 dB higher than psychophysical thresholds. The efficiency with which such ERA thresholds may be obtained with this method is substantially greater than that of conventional ERA procedures employing subjective evaluation of averages. Further, the technique allows variation of detection criteria to suit non-audiometric needs and empirical determination of the false-positive error rate under any set of conditions.

Auditory, Somatosensory and Visual Evoked Potentials in the Diagnosis of Neuropathology: Recording Considerations and Normative Data

Recent advances have led to an increased ability to use initial components of the human auditory (AEP) and visual (VEP) evoked potential as a neurophysiological probe for the detection of CNS disorders (for reviews see e.g., Starr et al., 1978; Halliday, 1978). These advances were quickly followed by a successful search for subcortical portions of the somatosensory evoked potential (SEP) which could be applied similarly to neurological problems (Matthews et al., 1974; Cracco and Cracco, 1976; Jones, 1977; Hume and Cant, 1978). For purposes of differential diagnosis and better localization of lesions it will often be desirable to record EPs to the three modalities of stimulation. A few studies have already appeared using combinations of EPs (e.g., Mastaglia et al., 1976; Stockard and Sharbrough, 1978). The need thus arises for a review of the problems involved in combining AEP, SEP and VEP recording in a test which can be carried out in a single recording session. This paper will consider recording conditions and available normative data in such a clinical context. In referring to electrode location the subscripts c and i will denote locations contralateral and ipsilateral to the side of stimulation. All components are labelled by their polarity and approximate peak latency; AEP components P2-P9 correspond to waves I-VII as usually described.

Somatic evoked potential evaluation of cerebral status in Reye syndrome.

Median nerve somatic evoked potentials (SEPs) were serially recorded in 12 Reye syndrome patients from shortly after admission to discharge. Recovery was clinically satisfactory in nine, unsatisfactory in two, and one died. All SEP components were absent or markedly depressed in initial recordings. Early progressive recovery of primary cortical components was associated with patient survival; lack of it was associated with death. Progressive recovery of SEP components later than 100 msec was associated with satisfactory clinical recovery; failure of recovery of these components was associated with residual neuropsychological deficit. Evaluation of late component recovery required comparison with age-dependent SEP configurations in normal children which differ from adults. We conclude that serial SEP recording is of significant value and superior to the EEG in early prognosis for survival, prognosis for clinically satisfactory or unsatisfactory recovery, and general evaluation of neurologic status in Reye syndrome.