The thalamo-cortical projection of the so-called posterior nuclear group: a study with anterograde degeneration methods in the cat.

Abstract

The ascending connections of the posterior nuclear group have been studied in the cat by the use of modified Nauta and Fink-Heimer techniques. Electrolytic lesions of various size were placed within the thalamus by means of trans-cerebellar stereotaxic approaches designed to avoid damage to the neocortex. The present observations suggest that virtually all of the cortical areas lying alongside auditory cortex, including those regions embracing the caudal part of the second somatic sensory field, receive fiber projections from the posterior nuclear group. Cases of restricted lesion further suggest that individually distinct contributions to this broad thalamo-cortical projection arise in various subdivisions of the territory. By contrast, fiber degeneration clearly attributable to lesions of the posterior nuclear group was not observed in the major auditory areas with the possible exception of their peripheral margins. In addition to these thalamo-cortical projections, degenerating fibers could be traced to discrete subdivisions of the caudoputamen and basolateral amygdala in all cases of lesion to the posterior nuclear group. The organization of these afferent connections of the posterior thalamus is discussed within the frame of a general categorization of sensory conduction routes in which each of a variety of ascending sensory pathways is interpreted as forming a lemniscal line system or lemniscal adjunct system.