Neuronal discharge rate is unsuitable for encoding sound intensity at the inferior-colliculus level.
Rate-intensity functions from single neurons in the central nucleus of the inferior colliculus (ICC) of the cat in response to tone bursts and continuous noise were recorded. Only 6% of 64 quantitatively studied neurons had monotonic functions in response to tone bursts, 12.5% in response to continuous noise. The other neurons had functions with a single peak which could occur at any super-threshold level tested (3-80 dB), or with multiple peaks. In 78% of the neurons the rate-intensity functions in response to tones and noise were of different shape. We interpret this stimulus dependency of the shape of rate-intensity functions of most neurons as evidence against sound-intensity coding only on the basis of the shape of rate-intensity functions at the ICC level. Rate-intensity functions averaged from neurons with similar characteristic frequencies or from all neurons of our sample indicate a constant average discharge over at least 60 dB sound intensity. This excludes sound-intensity coding by means of an average neuronal discharge rate in the ICC.
Ehret
G
G
Fakultät für Biologie, Universität Konstanz, F.R.G.
Merzenich
M M
MM
D000399:Air Pressure; D000818:Animals; D002415:Cats; D007245:Inferior Colliculi / Q000502:physiology*; D008144:Loudness Perception / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D009622:Noise; D013016:Sound