Neocortical and caudate projections of intralaminar thalamic neurons and their synaptic excitation from midbrain reticular core

Publisher Website
Google Scholar
Abstract
Neurons histologically localized in the centralis lateralis and paracentralis thalamic nuclei (CL-Pc) were recorded extracellularly in chronically implanted, unanesthetized cats. Neurons were antidromically activated from the pericruciate or suprasylvian gyri, or the caudate nucleus and synaptically activated from the mesencephalic reticular formation. Of 600 CL-Pc neurons tested with cortical stimulation, 39% were antidromically identified. Among the 600 CL-Pc cells, 170 were also tested with caudate stimulation and 22% of them were antidromically activated. CL-Pc neurons do not bifurcate to the caudate nucleus and the cortex. Instead, the 2 projections arise in separate neurons of different conduction velocities. CL-Pc neurons projecting to the caudate nucleus have conduction velocities (median, 3.8 m/s) significantly slower than those to different neocortical areas (median, 7.1-11.1 m/s). The projections of the CL-Pc nuclei to widespread cortical regions stem from aggregations of neurons, each of which projects to a particular cortical locus. Neurons do not bifurcate to the pericruciate and suprasylvian gyri: only 1 neuron was backfired from both cortical regions. Stimulation sites from which CL-Pc neurons could be antidromically activated were relatively restricted. The conduction velocity of thalamocortical CL-Pc neurons was significantly lower for those projecting to the anterior suprasylvian gyrus (median, 7.1 m/s) than those to the pericruciate areas (median, 9.6-11.1 m/s). Of all CL-Pc neurons with identified cortical or caudate projections, 13% were synaptically activated by midbrain reticular stimulation at latencies < 5 ms (mostly 1-2 ms). A distinct and homogeneous group of neurons was located in the large-celled, wing-like part of CL. They projected to area 5 and represented 10% of neurons backfired from that area, had high conduction velocities (30-50 m/s) and were synaptically activated from the midbrain reticular core with spike barrages (intraburst frequency of 800-1000 Hz). During wakefulness, the burst latency and duration diminished, as compared to synchronized sleep. The pathways from the midbrain reticular formation to the cortex are not comprised of a long series of neurons. A monosynaptic relay in the CL-Pc nuclei conveys midbrain reticular efferents to many separate cortical areas and to the caudate nucleus.

This publication has 26 references indexed in Scilit: