Ripple Analysis in Ferret Primary Auditory Cortex. 2. Topographic and Columnar Distribution of Ripple Response Parameters
MARYLAND UNIV COLLEGE PARK INST FOR SYSTEMS RESEARCH
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We examined the columnar and topographic distribution of response parameters using spectral ripples and tonal stimuli in the primary auditory cortex AI of the barbiturate- anesthetized ferret. The ripple stimuli consisted of broadband stimuli 1-20 kHz with sinusoidally modulated spectral envelopes. Responses to ripples were parametrized in terms of characteristic ripple OMEGAo ripple frequency where the magnitude of the ripple transfer function is maximal, i.e., where the cell responds best and characteristic phase PHIo intercept of the phase of the ripple transfer function, i.e., phase where the cell responds best. The response area measured with tones was parametrized in terms of its excitatory bandwidth at 20 dB above threshold BW2O, and its asymmetry as reflected by the directional sensitivity index C to frequency- modulated FM tones. Columnar organization for the above four parameters was investigated in 66 single units from 23 penetrations. It was confirmed for OMEGAo, PHIo, and the C index, but it appeared to be ambiguous for BW2O. The response parameters measured from multiunit recordings corresponded closely to those obtained from single units in the same cluster. In a local region, most cells exhibited closely matched response fields RFs, inverse Fourier transformed ripple transfer function and response areas measured with two-tone stimuli, and had correspondingly similar response parameters to ripples and tones. The topographic distribution of the response parameters across the surface of Al was studied with multiunit recordings in four animals.