Biomedical subjects
Publications and source records attributed to L H Mylin.
Primary VEP and cognitive auditory P300 studies were conducted in PD and related disorders. The relationship of afferent processing delays and their role and relationship in conscious sensory defects as well as their relevance to cognitive defects in this disease remains to be elucidated and requires further study.
Visual evoked potential (VEP) latency was measured in 89 patients with multiple sclerosis (MS) using both a checkerboard stimulus and an alternating vertical grating. Thirty-seven patients had abnormal VEP latencies to the check stimulus, but 63 were classified as abnormal when the grating stimulus was employed. In an additional 22 MS patients, each eye was tested with a checkerboard stimulus, a vertical grating, and a horizontal grating to determine if edge orientation of the stimuli was responsible for the difference between grating and check diagnostic yields. The resulting diagnostic differences could be explained by taking into account the sinusoidal components of these stimuli. After equating gratings and checks for the fundamental Fourier component, each eye of 15 of the MS patients was retested with gratings in three orientations: vertical, horizontal, and oblique. Nine of the 15 patients had an orientation-dependent abnormality of VEP latency. The results suggest that MS causes an orientational imbalance in the human visual system and that VEP testing with stimuli in more than one orientation can increase the diagnostic yield in MS patients.
Dynamic random dot correlograms (RDCs) produced by a rear-projection television system elicited visual evoked potentials (VEPs) in a sample of 10 observers corrected to emmetropia. When the observers viewed the RDCs binocularly through stereo wave length filters, characteristic wave forms were recorded. Four components were reliably recorded at the onset and the offset of the correlated state of the RDCs. These components differ with statistical significance (P less than 0.05) from each other. These RDC VEPs provide a practical technique to evaluate the integrity of binocular and, by inference, cortical processes.
Visual evoked potential (VEP) latency to a sinusoidal grating pattern was measured in each eye of 103 patients with multiple sclerosis (MS) and compared with results in a control group of 56 patients hospitalized for other neurological conditions. Of the 50 patients classified as having definite MS, 90% showed prolonged latency (over 131 msec) in one or both eyes. In each eye of 24 of the MS patients, psychophysical measurement of the detectability of grating patterns was obtained. This test was abnormal in 11 of 13 patients with definite MS, 3 of 4 with probable MS, and 5 of 7 with possible MS. There was no concordance between prolonged VEP latency and visual impairment as revealed by the psychophysical test. Apparently pathways determining VEP latency and spatial contrast detection may be unequally affected in MS.
Using a visual 'oddball' paradigm we studied ERPs in monkeys trained in a 'go' 'no-go' discrimination task. The stimuli were 2.5 cpd sinusoidal gratings differing only in orientation (0 degrees or 25 degrees). Monkeys released a lever during 1 of 2 response windows (RW), 480-1762 or 740-1672 msec, following target stimulus onset. Target stimulus presentation probabilities were 1.0, 0.5 and 0.3. The primary evoked potentials recorded to either the target or non-target stimulus were similar in all monkeys. P3 signals progressively emerged in the monkeys only to the target stimulus. P3 recorded at Cz, P3, and P4 had similar mean latencies and amplitudes. Eye movements showed no relationship to P3 potentials. Neither the primary visual potentials nor P3 changed significantly as a function of RW. P3 amplitude was inversely related to target probability. When the target stimulus was presented 100% of the time (P = 1.0) P3 disappeared over 4-5 blocks of trials, while the primary evoked potentials remained consistent.
Transient evoked potentials were recorded simultaneously over 5 electrodes placed in a horizontal row across the occiput. A range of spatial frequencies were presented as either full-field or hemifield stimuli. Subjects were 11 normal observers and 5 patients with lesions causing a homonymous hemianopic field defect. The shortest latency peak response was at approximately 70 msec, a negative potential (N70). For all spatial frequencies, full-field stimuli evoked a lower amplitude N70 at the midline than the sum of N70 amplitudes to two hemifield stimuli, suggesting partial cancellation. The latency and amplitude of N70 increased as spatial frequency increased. N70 and P100 differed in respect to their response to spatial frequency and field size, further suggesting that they may not be subsets of a unitary response. For hemifield stimulation, N70 had an ipsilateral maximum and attenuated or completely reversed in polarity across the midline. Consistent with the data of normals using hemifield stimuli, in 5 patients a full-field stimulus elicited an N70 lateralized contralaterally to the homonymous hemianopia, i.e., the ipsilateral N70 was absent. The absolute amplitude difference between the left and right electrodes was significant for hemifield stimulation in normals and full-field stimulation in the patients, but not for full-field stimulation in normals. Our results imply that the evaluation of N70 hemispheric distribution is useful for the evaluation of paramacular visual field defects.