Projection pattern of functional components of thalamic ventrobasal complex on monkey somatosensory cortex

Publisher Website
Google Scholar
Abstract
The thalamic ventrobasal complex (VB) was explored for single and multiunit responses to natural somesthetic stimuli in barbiturate-anesthetized monkey [Macaca fascicularis and M. nemestrina]. The cortical projection of functionally defined parts of VB was then examined by injection of minimal quantities of tritiated amino acids at defined sites in these parts. The extent of VB was identified by recording from brains in which lemniscal terminations was labeled by injection of anterograde tracers in the dorsal column nuclei. The results confirm the subdivision of VB into a large central core of neurons responsive to cutaneous stimuli and a thinner anterodorsal shell of neurons responsive only to stimulation of deep tissues. The inner part of the central cutaneous core projects only to area 3b; parts of the core situated dorsal, ventral and posterior to this project to areas 3b and 1; the deep shell projects to areas 3a and 2. Microelectrodes entering VB horizontally from behind encounter sequences of neurons whose receptive fields do not change for several hundred micrometers as the electrode advances anteriorly. Microelectrodes traversing VB from anterolateral to posteromedial successively encounter neurons whose receptive fields change rapidly over distances as little as 100 .mu.m. Anteroposterior rows of microelectrode penetrations traversing the dorsoventral extent of VB in the same parasagittal plane encounter sequences of neurons whose receptive fields gradually shift from proximal to distal body parts. But the same receptive fields tend to be encountered at the same depth by the different microelectrodes. Anteroposteriorly elongated injections of isotope in VB label a far less extensive part of areas 3a, 3b, 1 or 2 than mediolaterally or dorsoventrally elongated injections. A fundamental organization of VB in which narrow, anteroposteriorly elongated components of VB represent small parts of the body surface and project differentially on the cytoarchitectonic fields of the 1st somatosensory area is suggested.