Nucleus isthmus of toad is secondary visual center.

Visual responses of 148 units have been recorded with micropipettes from the left nucleus isthmus areas of toads (Bufo bufo gargarizans), their auditory and tactile responses also examined, and 122 recording sites marked with cobalt sulphide. This study indicates that: (i) 118 units responding solely to visual stimuli are found within the nucleus, and 4 multisensory units outside, (ii) there exist a visual field map and binocular units in the nucleus, and (iii) response latencies of the isthmic units to a spot of light range from 120 to 540 msec, with no correlation with recording sites.