Saturday, September 7, 2024
9/7/2024
PROJECT SUMMARY Brain responses to stimuli are not static over time but are dynamically modulated by the context of concurrent and preceding stimuli. This supports the rapid detection of behaviorally relevant information which may be key for survival in complex environments. In the visual system, neural activity as early as primary visual cortex (V1) is increased to stimuli that deviate from contextual patterns, a phenomenon termed “deviance detection.” In human EEG recordings, this deviance detection is reflected in the “mismatch negativity”, an early scalp potential elicited by rare stimuli in, for example, an “oddball” sequence. Visual mismatch negativity, and likely deviance detection, is altered in many neurological and psychiatric disorders, indexing fundamental visual processing deficits that may undermine how affected individuals relate to their world. Despite this basic and clinical significance, the neural circuitry for generating deviance detection is unknown. Our past work has utilized mice to address this question at a basic level, given the powerful set of genetic and optical tools available in this animal. We identified robust deviance detection in mouse V1, particularly in pyramidal neurons (PYRs) in superficial cortical layers (layer 2/3). We then showed that V1 deviance detection is dependent on i) local GABAergic interneurons and ii) top-down inputs from higher cortical areas (anterior cingulate; ACa). Exactly how these circuit elements interact to modulate V1 activity in context, producing deviance detection to novel stimuli, is unclear. The current project will build these preliminary insights to test a detailed circuit hypothesis of how deviance detection responses emerge in V1 in layer 2/3. Specifically, we propose that top-down input to V1 (from ACa) engages a mutually inhibitory interneuron circuit, involving namely vasoactive intestinal peptide- (VIP) and somatostatin- (SST) neurons. This serves to transiently modulate the excitability of subsets of PYRs dependent on their feature selectivity, attenuating responses to redundant stimuli and augmenting responses to deviant stimuli. To test this hypothesis, we will present visual “oddball” and control sequences to awake mice (which allows us to parse true deviance detection from the absence of simple neural adaption). We will employ two- photon calcium imaging and spatiotemporally precise optogenetic interventions (one and two-photon) to record and manipulate cell-type specific activity dynamics in V1. In aim 1, we will optically probe PYR excitability with single cell resolution during specific phases of the oddball paradigm, assessing PYR responses relative to their feature selectivity. Next, we will optically suppress SST and VIPs in V1 (aim 2) and then top-down ACa inputs to V1 (aim 3) at specific phases of the oddball paradigm while recording PYRs, SSTs, and VIPs to precisely test predictions of our circuit hypothesis. This focused, technologically advanced approach, applied during a passive and highly translatable sensory stimulation paradigm, will provide fundamental insights which could transform how basic visual processing and central visual circuitry is studied and understood in health and disease.
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