Disturbance of delayed match-to-sample in macaques by tetanization of anterior commissure versus limbic system or basal ganglia

Three pig-tailed macaques were trained to select ("match") from a pair of colored images that which they had seen ("sample") and responded to 5--15 s previously. The anterior commissure (AC) and/or its radiation, various loci in basal ganglia, hippocampal formation and "control" areas, (splenium of corpus callosum, precentral gyrus, insular cortex), totalling 40 loci, were each tetanized for 4 s during presentation of the "sample" image, during the delay period, or when the monkey was required to select the "matching" image. For several loci in the hippocampal formation tetanization at any phase of the task reduced "matching" to chance levels and gave evidence of electrical after-discharge; but other comparable hippocampal loci had little or no effect. Response to "sample" or "match" stimuli were absent during tetanization of basal ganglia or anterior commissure. When finally made, upon cessation of tetanization, responses were equally correct for basal ganglia and "control" sites, but for AC were at chance levels.