Abstract
1) Augmenting and recruiting responses in the sensory cortices were examined by means of laminar field potential analysis in the cortices. These responses were characterized and interpreted as follows: Augmenting responses are a deep thalamocortical (T-C) response followed by a superficial T-C response and recruiting responses are a pure form of superficial T-C response, deep and superficial T-C responses being two elementary components constituting various cortical responses induced by thalamic stimulation (see SASAKI et al., 1970).
2) Long-latency surface-negative potentials elicited in the somatosensory cortex (posterior sigmoid gyrus) by repetitive stimulation of the intralaminar thalamic nuclei were not due to recruiting responses actually generated in this area but attributable to the responses evoked in the underlying hidden cortex. Similar situations to those in the somatosensory cortex hold for “recruiting responses” recorded on the surface of the visual and auditory areas, i. e., the responses in the lateral and the ectosylvian gyri were assignable to activities generated in the underlying or neighboring hidden cortex.
3) Repetitive stimulation of the thalamic sensory relay nuclei given at a low frequency failed to evoke the augmenting response in the respective cortical sensory areas. It induced in some cases incremental responses in the sensory areas of the cortex; the depth profiles in the cortex were not in accord with the characteristic feature of the augmenting response in the anterior sigmoid gyrus.
4) The absence of superficial T-C responses in the form of recruiting responses as well as a component of augmenting responses in the sensory cortices suggests that there is little or no thalamocortical projection system for the superficial T-C response ending in these cortices.
