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 medialis thalamic nucleus (LM) of the cat resulted in labeled neurons in cortical and subcortical structures that averaged 71% and 29%, respectively. Every LM sector receives abundant projections from the polymodal sylvian anterior cortical area, the reticular thalamic nucleus, and the stratum opticum and intermediate layer of the superior colliculus. Less abundant but consistent projections were detected in cingular, auditory II, lateral suprasylvian and anterior ectosylvian visual cortices, and cortical area 7. A topographical distribution of afferent connections to different LM sectors arising from other cortical and subcortical structures could be established. The ventromedial sector receives connections mainly from the insular agranular, limic and prefrontal cortical areas, as well as from brain stem structures and the contralateral pretectal region. The dorsolateral sector is mainly related to cortical areas and subcortical structures processing visual information. The existence of overlap among neuronal LM populations receiving and sending connections to and from various cortical areas suggests that this nucleus is an appropriate substrate for effective interaction between different and distant cortical areas.