Sensory response properties of cortical neurons in the anterior ectosylvian sulcus of cats: intracellular recording and labeling

Abstract

Visual and auditory sensory responses of cortical neurons in the caudal half of the anterior ectosylvian sulcus (AES) of cats were examined under α-chloralose anesthesia, using intracellular recording and labeling techniques. Stable intracellular recordings were obtained from 155 neurons, and 141 neurons exhibited responses to sensory stimuli. Of 141 sensory neurons, 74 (52%) were bimodal neurons that responded to both visual and auditory stimuli, and 67 (48%) were unimodal showing sensory responses only to visual (25) or auditory stimulation (42). Forty-five neurons (35 pyramidal neurons, 5 non-pyramidal neurons, 5 not classified) responsive to sensory stimuli were labeled with biocytin. The percentage of bimodal neurons of the biocytin-labeled neurons was 40% ( 4 10 ) in layer II, 50% ( 10 20 ) in layer III–IV, 70% ( 7 10 ) in layer V and 60%/) ( 3 5 ) in layer VI. Thus the convergence of visual and auditory inputs on single neurons was most intense in layer V. Auditory response latencies were in a narrow range from 10 to 40 ms, whereas visual response latencies were in a wide range from 15 to 100 ms. Late visual responses (> 60 ms) were more commonly elicited in bimodal neurons than in visual unimodal neurons. Visual responses in layer 11 were all elicited over 40 ms, whereas early visual responses within 40 ms were observed in the other cortical layers. A subgroup of neurons ( 22 141 ) had a propensity to exhibit a burst discharge, a train of three to seven action potentials on a deploarizing envelope in response to sensory stimuli. Their specific distribution in cortical tissue was suggested by the result that six out of nine biocytin-labeled neurons (seven pyramidal neurons, two non-pyramidal neurons) showing burst discharges to sensory stimuli were observed in layer V. These results are considered to signify some aspects of intracortical organization related to the cross-modal integration of sensory inputs.