Functional subdivisions of the temporal lobe neocortex

Abstract

In order to gather evidence on functional subdivisions of the temporal lobe neocortex of the primate, the activity of more than 2600 single neurons was recorded in 10 myelo- and cytoarchitecturally defined subdivisions of the cortex in the superior temporal sulcus (STS) and inferior temporal gyrus of the anterior part of the temporal lobe of 5 hemispheres of 3 macaque monkeys. First, convergence of different modalities into each area was investigated. Areas TS and TAa, in the upper part of this region, were found to receive visual as well as auditory inputs. Areas TPO, PGa, and IPa, in the depths of the STS, received visual, auditory, and somatosensory inputs. Areas TEa, TEm, TE3, TE2, and TE1, which extend from the ventral bank of the STS through the inferior temporal gyrus, were primarily unimodal visual areas. Second, of the cells with visual responses, it was found that some neurons in areas TS-IPa could be activated only by moving visual stimuli, whereas the great majority of neurons in areas TEa-TE1 could be activated by stationary visual stimuli. Third, it was found that there were few sharply discriminating visual neurons in areas TS and TAa; of the sharply discriminating visual neurons in other areas, however, neurons that responded primarily to faces were found predominantly in areas TPO, TEa, and TEm (in which they represented 20% of the neurons with visual responses); neurons that were tuned to relatively simple visual stimuli such as sine-wave gratings, color, or simple shapes were relatively common in areas TEa, TEm, and TE3; and neurons that responded only to complex visual stimuli were common in areas IPa, TEa, TEm, and TE3. These findings show inter alia that areas TPO, PGa, and IPa are multimodal, that the inferior temporal gyrus areas are primarily unimodal, that there are areas in the cortex in the anterior and dorsal part of the STS that are specialized for the analysis of moving visual stimuli, that neurons responsive primarily to faces are found predominantly in areas TPO, TEa, and TEm, and that architectural subdivisions of the temporal lobe cortex are related to neuronal response properties.