Characteristics of interhemispheric impulse conduction between prelunate gyri of the rhesus monkey

Cells of origin of the corpus callosum (callosal efferent neurons) in prelunate gyrus (area OA) of the rhesus monkey were studied using electrophysiological techniques. Monkeys were chronically prepared and callosal efferent neurons were identified by their antidromic activation following electrical stimulation of the contralateral prelunate gyrus and/or the splenium of the corpus callosum. Interhemispheric antidromic latencies ranged from 2.6--18.0 ms (median = 7.0 ms) while the conduction velocity along the length of the axon ranged from 2.8 to 22.5 M/s (median = 7.4 M/s) while the conduction velocity along the length of the axon ranged from 2.8 to 22.5 M/s (median = 7.4 M/s. Following the relative refractory period of a single prior impulse, all but one of 61 callosal efferent neurons studied showed a supernormal period of increased axonal conduction velocity and excitability. Following several prior impulses, the supernormal period was followed by a subnormal period of decreased axonal conduction velocity and excitability, which, depending on the number of prior impulses, lasted from several hundred ms to nearly 2 min.