Mukesh, A. | bioRxiv Science

bioRxiv2021

Separate functional subnetworks of excitatory neurons show preference to periodic and random sound structures

Auditory cortex (ACX) neurons are sensitive to spectro-temporal sound patterns and violations in patterns induced by rare stimuli embedded within streams of sounds. We investigate the auditory cortical representation of repeated presentations of sequences of sounds with standard stimuli (common) with an embedded deviant (rare) stimulus in two conditions - Periodic (Fixed deviant position) or Random (Random deviant position), using extracellular single-unit and 2-photon Ca+2 imaging recordings in Layer 2/3 neurons of the mouse ACX. In the population average, responses increased over repetitions in the Random-condition and were suppressed or did not change in the Periodic-condition, showing irregularity preference. A subset of neurons also showed the opposite behavior, indicating regularity preference. Pairwise noise correlations were higher in Random-condition over Periodic-condition, suggesting the role of recurrent connections. 2-photon Ca+2 imaging of excitatory (EX) and parvalbumin-positive (PV) and somatostatin-positive (SOM) inhibitory neurons, showed different categories of adaptation or change in response over repetitions (categorized by the sign of the slope of change) as observed with single units. However, the examination of functional connectivity between pairs of neurons of different categories showed that EX-PV connections behaved opposite to the EX-EX and EX-SOM pairs that show more functional connections outside category in Random-condition than Periodic-condition. Finally considering Regularity preference, Irregularity preference and no preference categories, showed that EX-EX and EX-SOM connections to be in largely separate functional subnetworks with the different preferences, while EX-PV connections were more spread. Thus separate subnetworks could underly the coding of periodic and random sound sequences. Significance StatementStudying how the ACX neurons respond to streams of sound sequences help us understand the importance of changes in dynamic acoustic noisy scenes around us. Humans and animals are sensitive to regularity and its violations in sound sequences. Psychophysical tasks in humans show that auditory brain differentially responds to periodic and random structures, independent of the listeners attentional states. Here we show that mouse ACX L2/3 neurons detect a change and respond differentially to changing patterns over long-time scales. The differential functional connectivity profile obtained in response to two different sound contexts, suggest the stronger role of recurrent connections in the auditory cortical network. Furthermore, the excitatory-inhibitory neuronal interactions can contribute to detecting the changing sound patterns.

neuroscience↗

bioRxiv2019

Earliest experience of rare but not frequent sounds causes long term changes in the adult auditory cortex

Sensory experience during a critical period alters sensory cortical responses and organization. We find that the earliest sound driven activity in the mouse auditory cortex (ACX) starts before ear-canal opening (ECO). Effects of auditory experience before ECO on ACX development are unknown. We find that mouse ACX subplate neurons (SPNs), crucial in thalamocortical maturation, respond to sounds before ECO showing oddball selectivity. Before ECO, SPNs are more selective to oddball sounds in auditory streams than thalamo-recipient layer 4 (L4) neurons and not after ECO. We hypothesize that SPNs oddball selectivity can direct development of L4 responses before ECO. Exposing mice before ECO with a rarely occurring tone in a stream of another tone occurring frequently leads to the strengthening of the adult cortical representation of the rare tone, but not that of the frequent tone. Results of control exposure experiments at multiple developmental windows and also with only a single tone corroborate the observations. A computational network model of known thalamic inputs to SPNs and L4 explains the observed developmental plasticity. Information-theoretic analysis with sparse coding assumptions also predicts the observations. Thus, salient low probability sounds in the earliest auditory environment cause long term changes in the ACX.

neuroscience↗