| Research Abstract |
Surface-negative, depth-positive (s-N, d-P) cortical field potentials (readiness potentials) were recorded in the posterior parietal cortex (the posterior bank of the intraparietal sulcus) preceding self-paced hand movements in the monkey. We supposed the thalamus to be an origin of the potentials according to previous morphological investigations. The depth profile of cortical field potentials by thalamic stimulation was examined with a glass micropipette under pentobarbital anesthesia in the monkey. Stimulation of nucleus pulvinaris induced s-N, d-P potentials (superficial thalamo-cortical responses) in the posterior bank of the intraparietal sulcus (IPS). The polarity of the potentials was reversed at a cortical depth of 1700-1800 μm. Next, we identified thalamic nuclei the stimulation of which elicited superficial thalamo-cortical responses in the posterior parietal cortex by recording field potentials in the monkey with electrodes chronically implanted on the cortical surface and
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at a 2.0-3.0 mm cortical depth. Such nuclei were the nucleus lateralis posterior (LP), nucleus ventralis posterior lateralis pars caudalis (VPLc), and nucleus pulvinaris pars lateralis (Pul.l) and medialis (Pul.m). LP and VPLc projected mainly onto the superior parietal lobule (SPL) and the anterior bank of IPS, and Pul.m mainly onto the inferior parietal lobule (IPL) and the posterior bank of IPS. Pul.l had projections onto all of SPL, IPL and both the banks. Therefore, Pul.m was supposed to be a candidate of sources of the readiness potentials. Pul.m receives projections from the cingulate cortex. The readiness potentials could be generated by the projection from the cingulate cortex Pul.m to the posterior bank of IPS. Stimulation of the posterior cingulate cortex (Brodmann area 23) induced s-N, d-P cortical field potentials in the posterior bank of IPS. However, a relay of the potentials in the thalamus was not confirmed as lidocaine injection into the thalamus hardly eliminated them. Less
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