Interaction of excitatory and inhibitory frequency-receptive fields in determining fundamental frequency sensitivity of primary auditory cortex neurons in awake cats.
Harmonic complex tones produce pitch-height perception corresponding to the fundamental frequency (F0). This study investigates how the spectral cue of F0 is processed in neurons of the primary auditory cortex (A1) with sustained-response properties. We found F0-sensitive and -insensitive cells: the former discriminated between harmonics and noise, while the latter did not. F0-sensitive cells preferred F0s corresponding to the best frequency (BF) and 0.5 x BF. The F0-sensitivity to F0=0.5 x BF was preserved for missing F0, but abolished by eliminating both F0 and the second harmonic. The inhibitory subfield of the frequency-receptive field was restricted to the spectral region between the preferred harmonics in F0-sensitive cells, while it was frequency unspecific in F0-insensitive cells. We conclude that (i) A1 is well organized for discrimination between harmonics and noise; (ii) pitch-height is represented along with the tonotopic axis; (iii) all aspects of the sustained neural responses to harmonic and noise stimuli are consequences of spectral filtering; and (iv) although the observed cell behavior explains some psychophysical pitch perception behaviors, such as pitch-chroma (helical pitch perception with frequency elevation), pitch-level tolerance and adaptive behavior, F0-encoding in A1 remains at the incomplete perceptual level (dominance of the third to fifth harmonics for pitch strength is unexplainable by the cell behavior).
Qin
Ling
L
Department of Physiology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Tamaho, Yamanashi 409-3898, Japan.
Sakai
Masashi
M
Chimoto
Sohei
S
Sato
Yu
Y
D000161:Acoustic Stimulation; D000818:Animals; D001303:Auditory Cortex / Q000166:cytology / Q000502:physiology*; D002415:Cats; D003463:Cues; D009474:Neurons / Q000502:physiology*; D010898:Pitch Perception / Q000502:physiology*; D014851:Wakefulness / Q000502:physiology