SENSORY MODALITY DISTRIBUTION IN THE ANTERIOR ECTOSYLVIAN CORTEX (AEC) OF CATS

Modality specificity of neuronal responses to visual, somesthetic and auditory stimuli was investigated in the anterior ectosylvian cortex ( AEC) of cats, using single-unit recording techniques. Seven classes of neurons were found, and according to their responsiveness to sensory stimuli regrouped into three categories: unimodal, bimodal and trimoda l. Unimodal cells that responded to only one of the three stimulus mod alities formed 59% of the units; 30.2% were bimodal, in that they show ed a clear increase of neuronal discharges to two of the three stimulu s types; 10.8% were defined as trimodal because they responded to all three stimulus modalities. Although the different categories of cells were intermingled within the AEC, indicating a certain degree of overl ap between sensory modalities, some clustering of cell types was nonet heless evident. Thus, the somatosensory responsive cells were mainly l ocated in the anterior two-thirds of the dorsal bank of the anterior e ctosylvian sulcus. Visually responsive cells were concentrated on the ventral bank of the sulcus, whereas neurons with an auditory response occupied the banks and fundus of the posterior three-quarters of the s ulcus. The histological distribution and physiological properties of A EC neurons suggest that this cortical region is a higher-order associa tive area whose function may be to integrate information from differen t sensory modalities.