Spatial Interaction Between Spectral Integration and Frequency Gradient in Primary Auditory Cortex

Abstract

Primary sensory cortical areas are characterized by orderly and largely independent representations of several receptive field properties. This is expressed in multiple, spatially overlaying parameter distributions, such as orientation preference, spatial frequency, and ocular dominance maps in the primary visual cortex. In the auditory cortex, two main and presumably independent representational parameters are the center frequency and the frequency extent of spectral tuning curves. Here we demonstrate interactions between cortical tonotopic gradient and spectral bandwidth modules in cat primary auditory cortex (AI). First, the spatial representation of spectral integration is not equally expressed across the whole frequency range in AI. Narrow-bandwidth modules are found only in the mid-frequency region (5-20 kHz). Thus spectral integration properties delineate three frequency regions (<5, 5-20, and >20 kHz) in cat AI. Second, the extent of spectral integration covaries with the local tonotopic gradient in the low- and mid-frequency ranges. Regions with a shallow frequency gradient tend to have narrower spectral integration than those with a steep gradient. These relationships between spectral selectivity and frequency gradient constrain forebrain models of thalamo- and corticocortical convergence and connectivity and may reflect the processing of behaviorally relevant stimulus constellations.

Large-Scale Heterogeneous Representation of Sound Attributes in Rat Primary Auditory Cortex: From Unit Activity to Population Dynamics

“…The inverse of the parameter ⌬ shows a bell-shaped dependency (i.e., a decrease in the population susceptibility for the midfrequency region) with the carrier frequency ( f c ). This result is in agreement with the variations of the narrow (broad) bandwidth Q 10 (Q 40 ) along the anteroposterior axis of the A1 (Imaizumi and Schreiner, 2007). Middle and bottom, Distributions in A1 of the population codifiers of the modulation frequency and the amplitude, which were also heterogeneously distributed.…”

“…6, top, bottom left subplot), we found a decrease in the population susceptibility for the midfrequency region along the anteroposterior axis. In our opinion, this is caused by the increase in Q 10 and Q 40 in this region of A1, as was recently reported for cats [Imaizumi and Schreiner (2007), their Fig. 2].…”

Sound frequency representation in primary auditory cortex is level tolerant for moderately loud, complex sounds

“…This "overrepresentation" of the higher sound frequencies (in this case, particularly of the octave centered at 20 kHz; Fig. 2D) has been noted previously in cat AI (Imaizumi and Schreiner 2007) but is quite variable between cats (see, e.g., Fig. 8).…”

“…A pair of recent in vivo two-photon calcium imaging studies have indicated that, at the level of wellisolated units of presumably various cell types in layers II and III, the distribution of CFs appears more disordered on small distance scales (Bandyopadhyay et al 2010;Rothschild et al 2010). Thus more superficial layers of AI exhibit a more coarse tonotopy, a fact not entirely unexpected given the extensive frequency integration that occurs in AI (Happel et al 2010;Imaizumi and Schreiner 2007;Kaur et al 2004;Read et al 2001;Schreiner et al 2000;Wallace et al 1991;Winer 1992).…”

Spectral Integration in Primary Auditory Cortex Attributable to Temporally Precise Convergence of Thalamocortical and Intracortical Input

“…Consequently, cortical frequency tuning arises from the interaction and convergence of different subsets of concurring afferent, local, and long-range intracortical inputs. The spatial and temporal interaction of these different pathways during sound processing is still a matter of debate (L. M. Miller et al, 2001b;Imaizumi and Schreiner, 2007).…”