Complex tone processing in primary auditory cortex of the awake monkey. I.Neural ensemble correlates of roughness

Previous physiological studies [e.g., Bieser and Muller-Preuss, Exp. Brain Res. 108, 273-284 (1996); Schulze and Langner, J. Comp. Physiol. A 181, 651 -663 (1997); Steinschneider et al., J. Acoust. Sec. Am. 104, 2935-2955 (199 8)] have suggested that neural activity in primary auditory cortex (A1) pha se-locked to the waveform envelope of complex sounds with low (<300 Hz) per iodicities may represent a neural correlate of roughness perception. Howeve r, a correspondence between these temporal response patterns and human psyc hophysical boundaries of roughness has not yet been demonstrated. The prese nt study examined whether the degree of synchronized phase-locked activity of neuronal ensembles in A1 of the awake monkey evoked by complex tones par allels human psychoacoustic data defining the existence region and frequenc y dependence of roughness. Stimuli consisted of three consecutive harmonics of fundamental frequencies (f(0)s) ranging from 25 to 4000 Hz. The center frequency of the complex tones was fixed at the best frequency (BF) of the cortical sites, which ranged from 0.3 to 10 kHz. Neural ensemble activity i n the thalamorecipient zone (lower lamina III) and supragranular cortical l aminae (upper lamina III and lamina II) was measured using multiunit activi ty and current source density techniques and the degree of phase-locking to the f(0) was quantified by spectral analysis. In the thalamorecipient zone , the stimulus f(0) at which phase-locking was maximal increased with BF an d reached an upper limit between 75 and 150 Hz for BFs greater than about 3 kHz. Estimates of limiting phase-locking rates also increased with BF and approximated psychoacoustic values for the disappearance of roughness. Thes e physiological relationships parallel human perceptual data and therefore support the relevance of phase-locked activity of neuronal ensembles in Al for the physiological representation of roughness. (C) 2000 Acoustical Soci ety of America. [S0001-4966(00)05307-8].