Local versus global scales of organization in auditory cortex

Abstract

Topographic organization is a hallmark of sensory cortical organization. Topography is robust at spatial scales ranging from hundreds of microns to centimeters, but can dissolve at the level of neighboring neurons or subcellular compartments within a neuron. This dichotomous spatial organization is especially pronounced in the mouse auditory cortex, where an orderly tonotopic map can arise from heterogeneous frequency tuning between local neurons. Here, we address a debate surrounding the robustness of tonotopic organization in the auditory cortex that has persisted in some form for over forty years. Drawing from various cortical areas, cortical layers, recording methodologies, and species, we describe how auditory cortical circuitry can simultaneously support a globally systematic, yet locally heterogeneous representation of this fundamental sound property.

Functional imaging of neuronal activity of auditory cortex by using Cal-520 in anesthetized and awake mice

“…We confirmed a heterogeneous organization of the Au1 in both anesthetized and awake mice as described previously using OGB-1 or fluo-4 [9,15]. Therefore, our results with Cal-520 AM support the hypothesis of heterogeneity of the topographic organization in L2/3 local circuits in the Au1 [22], and provide a proof-of-principle for the use of Cal-520 for Au1 mapping experiments.…”

“…The inconsistent results in previous two-photon imaging-based mapping experiments in the Au1 can be explained by various reasons, including differences in recorded cortical areas, cortical layers, experimental methodologies, and species and brain states [22]. Among these reasons, the use of different indicators might be animportant possibility, although this aspect seems to be often ignored in the community.…”

Compensating Level-Dependent Frequency Representation in Auditory Cortex by Synaptic Integration of Corticocortical Input

“…Thereby, the presented synaptic population data of individual input systems is in accordance with recent anatomical findings [61]. Further, data from 2-photon imaging of single-cell spectral responses showed that is depends on laminar depth, afferent or intracortical inputs and hence the cortical processing hierarchy [16,17,62,63]. Corticocortical integration in neurons mainly receiving broad corticocortical inputs might hence contribute to the perceptual robustness across sound levels based on population coding [9,10,15].…”

Intracortical Circuits in Thalamorecipient Layers of Auditory Cortex Refine after Visual Deprivation

“…Although we detect refinement of L2/3 to L4 connections, intralaminar connections within L4 were not changed. Neighboring L4 neurons show higher similarity in their frequency selectivity than L2/3 neurons (Bandyopadhyay et al, 2010, Winkowski and Kanold, 2013, and Kanold et al, 2014), suggesting that the refinement we observe in L2/3 decreases connections between neurons of different frequency selectivity. Together with the strengthening of thalamocortical connections to L4 neurons after DE (Petrus et al, 2014), this indicates that DE causes a remodeling of all inputs to L4 neurons in A1 to improve sound processing.…”