Responses of single neurons in physiologically defined primary auditory cortex (AI) of the cat: frequency tuning and responses to intensity.

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Abstract
The responses of 383 single neurons to tonal stimuli in physiologically defined primary auditory cortex (AI) of barbiturate-anesthetized cats examined using sealed stimulating systems incorporating calibrated probe -microphone assemblies. Frequency-threshold curves were obtained for 196 cells and of these, 191 showed narrow frequency tuning. Sharpness of tuning was dependent on the best frequency (BF) of the units, but not on threshold at BF. Thresholds to BF tones were lowest for cells with BF in the range 4-12 kHz. In electrode penetrations normal or near normal to the cortex surface, cells had similar or identical BF tuning characteristics other than BF were not sytematically depth related. Spike count vs. intensity functions for BF tones were obtained for 61 cells; 80% of these cells had dynamic ranges of 40 dB or less; 14/61 cells had nonmonotonic intensity functions. Minimum latencies were obtained for 88 cells; latencies were shortest in the middle cortical layers. The frequency tuning of AI cells apparently reflects that of thalamic and brain stem auditory neurons. Convergence of information at the cortical level is not apparently reflected in the frequency-tuning properties of single neurons.