Monophasic pulse pair analysis of intracranial self-stimulation loci

Abstract

Monophasic pulse pair stimulation, traditionally used to determine the refractory characteristics of peripheral nervous system neurons, has been modified for the same purpose in intracranial self-stimulation (ICSS) behavior. When the interval between pulses in a pair (C-T interval) is systematically varied, ICSS response rates change as a function of this variation. The present study evaluated alterations in the C-T interval/ICSS response rate function across ICSS loci and across stimulation conditions. Diencephalic sites supported peak ICSS responding at significantly shorter C-T intervals than met-mesencephalic or telencephalic sites. Despite previously cited differences in ICSS behavior observed within diencephalic and within met-mesencephalic loci, no differences in ICSS responding across C-T intervals were observed within diencephalic and met-mesencephalic sites. Moreover, diencephalic sites produced peak ICSS responding at shorter C-T intervals when cathodal and anodal sources were distant than when they were adjacent; the relative proximity of cathodal and anodal sources did not affect met-mesencephalic ICSS behavior. These results suggest that alterations in ICSS responding across C-T intervals are due to differences in the locus and density of ICSS neurons in the cathodal field and the presence and/or absence of adjacent anodal influences as well as the refractory characteristics of the ICSS neurons.