Acoustic tuning of single cells in middle suprasylvian cortex of cat

Acoustic tuning of single cells in medial suprasylvian ‘association’ cortex (MSA) was studied in cats anesthetized with α-chloralose and in locally anesthetized cats immobilized with Flaxedil. MSA cells in the chloralose preparations exhibited little or no spontaneous activity and onset responses of variable latency to tone pulse stimuli. Tuning curves for these cells were extremely broad (extending over 4–5 octaves or more) and insensitive (thresholds of 40–60 dB SPL). Cells recorded from AI in the same preparations exhibited the sharp tuning and high sensitivity reported by others. In the immobilized animals, spontaneous firing rates of MSA cells were much higher and responses to tones were poorly defined and extremely labile. Thresholds could not easily be determined for many of these cells, but in some cases it was possible to establish approximate response areas. These cells exhibited a breadth of response and lack of sensitivity comparable to that seen under chloralose. The data indicate a high degree of convergence in the acoustic input to cells in MSA. Although inter-modality comparison is difficult, acoustic input to this area appears to be less specifically organized than visual input.