Organization of Somatic Afferents to the Diencephalon

Abstract

THREE main areas within the diencephalon are known to be concerned with somatosensory mechanisms; these are the ventrobasal complex, the intralaminar complex, and the posterior group. It is generally accepted that the afferents to the ventrobasal complex are organized in a simple somatotopic fashion^1,2, whereas the input to the intralaminar complex^3,4 and to the posterior group^4,5 is non-somatotopic and generally of long latency. The arrangement of afferents to the ventrobasal complex may be more complex than previously supposed^6,7, and the lateral thalamic nuclei may also be involved in somatosensory activity⁷. Furthermore, the properties of the nuclei of the dorsal column show a rostro-caudal differentiation^8,9, and it has been suggested that this is reflected in a differential termination of the medial lemniscus¹⁰. We have investigated the distribution of degeneration in the rat diencephalon using the Nauta method^11,12 after lesions made separately in the gracile and cuneate nuclei, the spinal cord at different levels from the spinomedullary junction to the lumbar region, and the trigeminal nuclear complex.