Journal of Neurophysiology, Vol 41, Issue 2 268-284, Copyright © 1978 by APS
Cytoarchitecture and thalamic connectivity of third somatosensory area of cat cerebral cortex
D. G. Tanji, S. P. Wise, R. W. Dykes and E. G. Jones
1. The third somatosensory area (SIII) was identified in the cat cerebral
cortex by the recording of surface potentials evoked by deflection of a
single contralateral mystacial vibrissa. A small amount of tritiated
leucine was then injected at the center of the focus of evoked activity
and, after a suitable survival period, the brain was prepared for
autoradiography. 2. As defined by the presence of an autoradiographic
injection, the SIII focus lay in a cytoarchitectonic field characterized in
particular by the presence of very large pyramidal cells in layer V and
corresponding to area 5a of Hassler and Muhs-Clement (24). 3. The terminal
ramifications of corticothalamic cells, as outlined by axoplasmically
transported label, formed clustered aggregations in the medial division of
the posterior group of thalamic nuclei (Pom) and not in the ventrobasal
complex (VB). This part of Pom is known to receive fibers from the spinal
cord. 4. Injections of horseradish peroxidase primarily affecting area 5a
retrogradely labeled cells in Pom but not in VB. 5. Injections of isotope
in the two other foci of vibrissa-evoked activity usually recorded in each
brain were invariably found to label a part of area 3b of the first
somatosensory area (SI) in the case of the more anterior focus. The second
focus sometimes lay in area 2 of SI and sometimes in the second
somatosensory area (SII).
