Sparse Representation in Awake Auditory Cortex: Cell-type Dependence, Synaptic Mechanisms, Developmental Emergence, and Modulation

Abstract

Sparse representation is considered an important coding strategy for cortical processing in various sensory modalities. It remains unclear how cortical sparseness arises and is being regulated. Here, unbiased recordings from primary auditory cortex of awake adult mice revealed salient sparseness in layer (L)2/3, with a majority of excitatory neurons exhibiting no increased spiking in response to each of sound types tested. Sparse representation was not observed in parvalbumin (PV) inhibitory neurons. The nonresponding neurons did receive auditory-evoked synaptic inputs, marked by weaker excitation and lower excitation/inhibition (E/I) ratios than responding cells. Sparse representation arises during development in an experience-dependent manner, accompanied by differential changes of excitatory input strength and a transition from unimodal to bimodal distribution of E/I ratios. Sparseness level could be reduced by suppressing PV or L1 inhibitory neurons. Thus, sparse representation may be dynamically regulated via modulating E/I balance, optimizing cortical representation of the external sensory world.

Tonotopic and non-auditory organization of the mouse dorsal inferior colliculus revealed by two-photon imaging

“…The microheterogeneity was similar for GABAergic and glutamatergic neurons. Our results thus differ from auditory cortex, where response patterns are different and local microheterogeneity is much smaller for (parvalbumin-positive) GABAergic neurons than for glutamatergic neurons (Maor et al, 2016; Liang et al, 2018; Liu et al, 2019). We conclude that despite the shared input and firing behavior during development (Babola et al, 2018), functional heterogeneity dominates within bands in the dorsal IC of adult mice.…”

Local homogeneity of tonotopic organization in the primary auditory cortex of marmosets

“…The precision of tonotopic organization at the cellular level has recently become a controversial issue (34)(35)(36)(37)(38)(39), based mostly on studies from mice. Although a tonotopic map of monkey A1 at the cellular level has not been reported, previous studies using extracellular electrophysiological recording of neuronal activities have suggested that the tonotopic preference of cortical cells within local regions of A1 is homogeneous, consistent with a smooth tonotopic organization.…”

Temporary Visual Deprivation Causes Decorrelation of Spatiotemporal Population Responses in Adult Mouse Auditory Cortex

“…Recent studies revealed that A1 responses sparsify with development and that auditory experience early in life can shape this process (Liang et al, 2019; Meng et al, 2019). We here show that visual experience later in life has a similar capability.…”