Suppression of auditory cortical activities in awake cats by pure tone stimuli

Based on the time courses of excitatory spike-responses to pure-tone stimuli, neurons in the primary auditory cortex (A1) of awake cats have been classified into the phasic cell (P-cell), the tonic cell (T-cell), and the phasic-tonic cell (PT-cell). In the present study, taking advantage of the presence of the spontaneous spike-activities of A1 neurons in awake animals, time courses of suppressive spike-responses to pure-tone stimuli were studied by constructing spectro-temporal spike-activity diagrams. In P-cell, the suppression and excitation temporally alternated and spectrally co-occurred, restricting excitatory spike-responses within narrow temporal limits but not setting the spectral limits. In T-cell, the suppression and excitation spectrally alternated and temporally co-occurred, restricting excitatory frequency-tuning but not setting the time limits. PT-cell has mixed response properties of P- and T-cells. The findings suggest that: (1) P-cell analyzes temporal information of the sound without active spectral limits, (2) T-cell analyzes spectral information without limits of time, and (3) PT-cell analyzes spectrally and temporally complex auditory information. Taken in the light of recent findings that the shift of the balance of the synaptic excitation and inhibition results in the spike-activity modulation of the cerebral cortical neurons, it is suggested that the temporal shift of the balance of the excitation and inhibition works in P-cell; the spectral shift, in T-cell; and the combination of the temporal and spectral shifts, in PT-cell, underlying the functional differences between cell-types.