Stimulus dependence of spectro-temporal receptive fields in cat primary auditory cortex.

The frequency-tuning curve is a static representation of the neuron's sensitivity to stimulus frequency. The temporal aspects of the frequency sensitivity can be captured in the spectro-temporal receptive field (STRF), often presented as the average spectrogram of the stimulus preceding a spike but also as the average frequency-dependent post-stimulus time histogram (PSTH). The temporal envelope of the stimulus produces considerable smoothing, and as a consequence the PSTH representation is finer-grained than the spectrogram representation. Here we compare STRFs for 1/s and 20/s single-frequency stimuli with 120/s steady-state multi-frequency stimuli for 87 recording sites in primary auditory cortex of cats. For the 672 estimated STRFs, which for multi-frequency stimuli were mostly obtained at 55 dB SPL, we found lateral inhibition in 17% of the cases, in 32% post-activation suppression, and in 51% only excitation. In 35% of the recordings the excitatory frequency-tuning curves were very similar for single and multi-frequency stimuli, in the remaining 65% the common finding was the emergence of an intensity independent bandwidth for the multi-frequency stimuli. Comparison of the 20/s and 120/s stimuli showed that the resulting increase in inhibition was strongest in the center of the STRF.