Spectrotemporal Receptive Fields in the Lemniscal Auditory Thalamus and Cortex

Abstract

Receptive fields have been characterized independently in the lemniscal auditory thalamus and cortex, usually with spectrotemporally simple sounds tailored to a specific task. No studies have employed naturalistic stimuli to investigate the thalamocortical transformation in temporal, spectral, and aural domains simultaneously and under identical conditions. We recorded simultaneously in the ventral division of the medial geniculate body (MGBv) and in primary auditory cortex (AI) of the ketamine-anesthetized cat. Spectrotemporal receptive fields (STRFs) of single units (n = 387) were derived by reverse-correlation with a broadband and dynamically varying stimulus, the dynamic ripple. Spectral integration, as measured by excitatory bandwidth and spectral modulation preference, was similar across both stations (mean Q(1/e) thalamus = 5.8, cortex = 5.4; upper cutoff of spectral modulation transfer function, thalamus = 1.30 cycles/octave, cortex = 1.37 cycles/octave). Temporal modulation rates slowed by a factor of two from thalamus to cortex (mean preferred rate, thalamus = 32.4 Hz, cortex = 16.6 Hz; upper cutoff of temporal modulation transfer function, thalamus = 62.9 Hz, cortex = 37.4 Hz). We found no correlation between spectral and temporal integration properties, suggesting that the excitatory-inhibitory interactions underlying preference in each domain are largely independent. A small number of neurons in each station had highly asymmetric STRFs, evidence of frequency sweep selectivity, but the population showed no directional bias. Binaural preferences differed in their relative proportions, most notably an increased prevalence of excitatory contralateral-only cells in cortex (40%) versus thalamus (23%), indicating a reorganization of this parameter. By comparing simultaneously along multiple stimulus dimensions in both stations, these observations establish the global characteristics of the thalamocortical receptive field transformation.

Fine frequency tuning in monkey auditory cortex and thalamus

“…In anesthetized cats, frequency bandwidths have been measured in most stages of the ascending pathway. It has been shown that average frequency bandwidths increase from about 1/4th octave in the auditory nerve to about 1 octave in primary auditory cortex (A1) (Miller et al 2002;Moshitch et al 2006;Pickles 1979;Ramachandran et al 1999). A similar trend was observed in a number of primate studies (see Table 1).…”

Stimulus-invariant processing and spectrotemporal reverse correlation in primary auditory cortex

“…Such processing is already under study in auditory neurophysiology (Kowalski et al, 1996a,b;Depireux et al, 2001;Miller et al, 2001Miller et al, , 2002Escabí and Schreiner, 2002) and psychoacoustics (Chi et al, 1999), and is also being investigated for various signal-processing tasks, including audio coding (Atlas and Shamma, 2003;Klein et al, 2003) and speech recognition (Hermmansky, 1999;Nadeu et al, 2001;Kleinschmidt and Gelbart, 2002;Kleinschmidt, 2002).…”

“…Each spectrotemporal modulation frequency is the conjunction of a spectral and a temporal modulation frequency; the higher the spectral modulation frequency, the sharper the spectral feature (e.g., sharp peaks or edges in the spectrum), and the higher the temporal modulation frequency, the more abruptly that feature changes in time. As a population, the strongest phase-locked response in central auditory neurons occurs over a select range of low spectral and temporal modulation frequencies (Rees and Moller, 1983;Shamma et al, 1995;Schreiner and Calhoun, 1995;Kowalski et al, 1996a;Depireux et al, 2001;Sen et al, 2001;Miller et al, 2002;Escabí and Schreiner, 2002). Not surprisingly, the most fruitful stimuli have had spectrotemporal modulation frequencies concentrated within this range.…”

Spectral integration plasticity in cat auditory cortex induced by perceptual training

“…For example, tuning curves from cat cochlear nucleus neurons were predicted from the neuron's response to cosine noise (Bilsen et al 1975;ten Kate & van Bekkum 1988). More recently, cat auditory cortical neurons have been shown to respond selectively and systematically to acoustic stimuli with sinusoidal spectral envelopes (Schreiner & Calhoun 1994;Calhoun and Schreiner;Miller et al, 2002). Studies in ferret AI find that ripple responses allow predictions of responses to pure tones and to spectrally complex natural sounds Versnel and Shamma 1998;Klein et al, 2000) suggesting that AI neurons analyze the shape of acoustic spectra in a substantially linear manner.…”

“…Auditory gratings or ripple spectra, i.e. broad-band stimuli with sinusoidal spectral envelopes similar to the structure of vowels, have been used to characterize spectral integration properties of central auditory neurons (e.g., Schreiner and Calhoun, 1994;Shamma et al, 1995;Klein et al, 2000;Miller et al, 2002;Escabi and Schreiner, 2002). Cat and ferret cortical neurons respond preferentially to a narrow range of formant ratios or spectral envelope frequencies (Calhoun and Schreiner, 1998;Klein et al, 2000;Kowalski et al, 1996;Schreiner and Calhoun, 1994;Shamma et al, 1995).…”