Electrophysiology of the frontal granular cortex. III. The cingulate-prefrontal relation in primate.

An investigation of the nature of laminar potentials and impulse discharges of units of dorsolateral prefrontal cortex (FC) evoked by stimulations of cingulate gyrus was made in rhesus monkey. Anterior cingulate stimulations evoked 1.0--1.5 msec latency waves, positive on pial surface and negative at FC depths of about 500--2000 mum with about the same time scale. Following the positive wave there was also a negative wave response. The amplitude and duration of the surface positive wave and negative wave of response varied according to the state of background EEG of the area. During steady EEG the positive wave was well developed and the negative wave was incipient but during EEG oscillations, the positive wave was markedly diminished and the negative wave enlarged. The alteration of responsiveness was also confirmed in depths by changes of reversed polarity potentials corresponding temporally to surface potentials. Discrete responses of FC were evoked at stimulus frequencies of up to 20 Hz. Higher frequencies resulted in depression of responsiveness. Alternate responses were depressed between 20 and 40 Hz and all responses were progressively depressed with still higher frequencies. Impulse discharges of FC units were evoked either singly or in bursts by the cingulate stimulations. Single impulse responses were commonly found. Presumably monosynaptic responses were in the latency range of 1.2-3.0 msec. They were found at depths of about 500 mum and 1000 mum. Long latency (7 msec) responses were also observed in the upper levels of cortex. The latency of the unitary response of a multi-impulse burst was in the range of 6.5-16 msec and the frequency of impulses in burst was in the order of 500-750 Hz. Such burst responses occurred on the declining phase of the depth negative wave evoked by the cingulate stimulation. The anterior cingulate effects were found to be distributed on the prefrontal cortex from arcuate sulcus to two-thirds distance rostrally. The unit responses were more commonly found in laminae between 0.4 and 1.0 mm depth than at other depths. The cingulate effects on FC were not affected by lesion of nucleus medialis dorsalis thalami or by ablation of the pre-motor cortex. The study discloses a basis by which functional states of limbic cortex can powerfully modulate the functioning of prefrontal neocortex of primate.