Interactions of sensory and nonspecific thalamic inputs to cortical polysensory units in the squirrel monkey

Abstract

Possible influences of nonspecific thalamocortical projections on sensory responsiveness of single units of polysensory cortex were investigated. Sensory responses in the postarcuate polysensory area (PPA) of the squirrel monkey were paired with antecedent low-frequency (10/sec) trains of stimuli applied to intralaminar nonspecific thalamic nuclei, to elicit recruiting responses indicative of activation of the nonspecific system. Recruiting responses were more prominent in the PPA than primary cortex and, in PPA units, their elicitation typically suppressed the sensory responses with which they were paired, without similarly affecting unpaired inputs to PPA. The reduction in responsiveness persisted for several minutes after the period of pairing in about one-half of the PPA units examined. Primary sensory cortical units were not similarly affected. The data suggest that nonspecific thalamic nuclei project more strongly to polysensory than to primary sensory cortex and that these projections may have the capacity to modulate selectively the responsiveness of polysensory units to peripheral inputs. Possible implications of such plasticity concerning learning are discussed.