AFFERENT CONNECTIONS OF THE LATERALIS MEDIALIS THALAMIC NUCLEUS IN THE CAT

We have used anterograde and retrograde horseradish peroxidase tracing methods in this study. Peroxidase injections in the lateralis mediali s thalamic nucleus (LM) of the cat resulted in labeled neurons in cort ical and subcortical structures that averaged 71% and 29%, respectivel y. Every LM sector receives abundant projections from the polymodal sy lvian anterior cortical area, the reticular thalamic nucleus, and the stratum opticum and intermediate layer of the superior colliculus. Les s abundant but consistent projections were detected in cingular, audit ory II, lateral suprasylvian and anterior ectosylvian visual cortices, and cortical area 7. A topographical distribution of afferent connect ions to different LM sectors arising from other cortical and subcortic al structures could be established. The ventromedial sector receives c onnections mainly from the insular agranular, limbic and prefrontal co rtical areas, as well as from brain stem structures and the contralate ral pretectal region, The dorsolateral sector is mainly related to cor tical areas and subcortical structures processing visual information. The existence of overlap among neuronal LM populations receiving and s ending connections to and from various cortical areas suggests that th is nucleus is an appropriate substrate for effective interaction betwe en different and distant cortical areas.