VISUAL AND AUDITORY EVOKED POTENTIALS
Electrophysiological recordings can be used to evaluate the intactness of specific sensory systems, including the visual system and the auditory system. I. Visual evoked potentials.The visual stimulus is often an alternating flashing checkerboard (2 Hz), with recording done over the primary visual cortex in the midline. The normal latencies for recordings are 70 msec for N1 (negative 1), 100 msec for P1 (positive 1), and 140 msec for N2 (negative 2).
Damage to the retino-geniculocalcarine pathway may result in altered latencies and amplitudes. II. Brainstem auditory evoked responses or potentials (BAER). The auditory stimulus is a series of clicks or tones, with recording done over the temporal lobe auditory cortex. Seven distinctive peak latencies occur: I. distal auditory nerve; II. proximal auditory nerve; III. cochlear nuclei; IV. superior olivary complex; V. nucleus of the lateral lemniscus; VI. inferior colliculus; and VII. medial geniculate nucleus. Altered latencies and amplitudes may indicate damage or disruption to the auditory pathway at specific sites.