A single neuron activity in the secondary cortical auditory area in the cat.

Abstract

Discharges of a single neuron in response to tone bursts or continuous pure tones were studied in the secondary cortical auditory area of the cats under very light general anesthesia by means of hyperfine microelectrode technique. Difference of responses of a single neuron to sound stimulation was found between the primary and the secondary areas.(1) Small evoked potentials by tone burst stimulation were recorded from the regions adjacent to the primary area while in the remaining regions they were hardly found.(2) The thresholds of all neurons examined for any stimulating sounds were much higher in the secondary area than in the primary area.(3) The latencies of responses to tone bursts were generally much longer, though variable, in the secondary area than in the primary area.(4) Most neurons in the secondary area responded only to strong continuous pure tones and not to tone bursts alone. Their responsive frequency ranges were very wide. Sometimes, the prolonged after-discharges were observed.(5) Neurons were also encountered responding to tone burst alone. Their responses had the same feature as those of the primary area.(6) Measurements were done on the response areas of neurons. Some of them showed a characteristic properties similar to those in the primary area, while the others were different, the areas being wider and not having the distinct characteristic frequency.(7) By two sound stimulation facilitatory and suppressive interactions were observed on the single neuronal responses just as in the case of the primary area.(8) Tonotopic localisation was not clearly found in this area, because many neurons explored had no distinct characteristic frequencies. Even on the neurons having a narrow response area the situation was very complicated. In contrast to the primary area neurons were easy to be recorded from the lower half of the posterior ectosylvian gyrus.(9) From the results described above it may be concluded that neurons of the secondary area do not play an important role for the analysis of sound, i.e for the discrimination of pitch and intensity of sound, but rather have integrative functions for analyzed component sounds.