Central reticular path to intralaminar and reticular nuclei of thalamus for activating EEG related to consciousness

Abstract

Intralaminar nuclei include parafascicular, limitans, centrum medianum, central, paracentral and central lateral, all situated along the length of the internal medullary lamina of the dorsal thalamus. The reticular thalamic, tegmentothalamic and tectothalamic tracts end in these nuclei which give rise to fibers that go out to end in the reticular nucleus on the outer surface of the thalamus. The reticular nucleus sends non-specific fibers to all parts of the cerebral cortex. The parafascicular and nucleus limitans send fibers to the reticular nucleus from which fibers go to the occipital cortex. Centrum medianum, near its middle, sends fibers ventrally and out to the ventral part of the reticular nucleus. An intralaminar bundle of fibers comes out of the frontal end of centrum medianum and ends in the central, paracentral, central lateral and submedial nuclei. Large cells in the bundle send fibers ventrally and out to the lower part of the reticular nucleus. Central and paracentral nuclei send fibers in the internal medullary lamina to the central lateral nucleus. From this nucleus fibers pass over the lateral anterior nucleus to reach the dorsal margin of the reticular nucleus. Central, paracentral and submedial nuclei send fibers in the inferior thalamic peduncle to the anterior perforated substance, and also fibers forward to the reticular nucleus and frontal cortex. Some fibers cross in the massa intermedia. Ventral medial and ventral anterior nuclei send fibers into the frontal radiation to the reticular nucleus and visceral areas in the medial frontal, orbital, insular and inferior frontal cortex. Ventral thalamus sends fibers to the hypothalamus, pallida and prerubral nucleus. Reticular nucleus is the last link in the non-specific path to the cortex for EEG rhythms related to general consciousness. The non-specific neural system is distinct from specific sensory and other neural systems that activate the cortex. In the cortex the non-specific fibers from the reticular nucleus contact pyramidal and granule cells whose actions produce the non-specific EEG rhythms.