Neuronal responses in cat primary auditory cortex to natural and altered species-specific calls

We investigated how natural and morphed cat vocalizations are represented i n primary auditory cortex (AI). About 40% Of the neurons showed time-locked responses to major peaks in the vocalization envelope, 60% only responded at the onset. Simultaneously recorded multi-unit (MU) activity of these pea k-tracking neurons on separate electrodes was significantly more synchronou s during stimulation than under silence. Thus, the representation of the vo calizations is likely synchronously distributed across the cortex. The sum of the responses to the low and high frequency part of the meow. with the b oundary at 2.5 kHz, was larger than the neuronal response to the natural me ow itself, suggesting that strong lateral inhibition is shaping the respons e to the natural meow. In this sense, the neurons are combination-sensitive . The frequency-tuning properties and the response to amplitude-modulated t ones of the MU recordings can explain the responses to natural, and tempora lly and spectrally altered vocalizations. Analysis of the mutual informatio n in the firing rate suggests that the activity of at least 95 recording si tes in Al would be needed to reliably distinguish between the nine differen t vocalizations. This suggests that a distributed representation based on t emporal stimulus aspects may be more efficient than one based on firing rat e. (C) 2000 Elsevier Science B.V. All rights reserved.