Neural mechanisms of innate and learned odour-guided behavioural decisions and revisions in mice

Abstract

Animals exhibit instinctive and learned stimulus-guided behaviours to adapt to dynamic environments. These innate and learned behaviours engage different cortical brain regions; however, how the sensory processing area responds in two different contexts remains unexplored. In nature, sensory inputs are often noisy and dynamic, affecting the perceptual decision-making process. Metacognition research has shown that mice are aware of perceptual ambiguity and can rectify errors. This involves the revision and/or cessation of context-inappropriate responses, based on task demands. The prefrontal and cingulate cortices are primarily implicated in error monitoring and rectification. However, the role of early sensory regions in modulating behavioural decisions and revisions remains largely unknown. We investigated the pre-cortical mechanisms of modulating misconstrued behavioural responses using an olfactory Go/No-go discrimination task. This paradigm presents equiprobable rewarded and nonrewarded trials that require participants to withhold their responses in nonrewarded contexts. Despite reaching high discrimination accuracy, mice responded inappropriately in a few non-rewarded trials, showing two types of licking patterns. High perceptual ambiguity results in licking similar to rewarded trials (non-revision trials), whereas low perceptual ambiguity shows sparse and brief licks with higher interlick intervals (revision trials). We observed a marked increase in revision trials with learning, indicating improved error awareness. These trials comprised 5-25% of high-performance blocks and impacted response latency and accuracy in subsequent trials. The revision frequency varied according to the stimulus complexity. Enhancement of inhibitory synaptic signalling in the olfactory bulb (OB) leads to faster odour discrimination and fewer revisions, confirming pre-cortical control. We propose that mice demonstrate a learning strategy by optimising reward acquisition through rapid response adjustment following errors. Olfactory bulb interneurons enhance perceptual dissimilarity, affecting error awareness and revisions. Unlike learned behaviours, threat responses are innate and genetically predetermined, such as rodents' fear responses to a predator scent. Therefore, we utilised TMT (2,3,5-Trimethyl-3-thiazoline), a volatile sulfur-containing kairomone from fox faeces, which functions as a predatory cue causing avoidance and freezing in rodents, to investigate pre-cortical control over innate behaviour. The amygdala assigns emotional valence to sensory information, enabling instinctive behaviours such as exploration and freezing. Olfactory information reaches the amygdala via OB projection neurones, whereas inhibitory interneurons modulate OB output and refine odour perception. While the roles of the Amygdala and Periaqueductal Gray (PAG) in the regulation of defensive behaviours are well understood, the role of the OB remains unexplored. Although the roles of the Amygdala and Periaqueductal Gray (PAG) in regulating defensive behaviours are understood, the role of the OB remains largely unexplored. Hence, we studied OB inhibitory circuits in odour-driven defensive behaviours. In vivo calcium imaging showed higher GAD-65-expressing OB interneuron activity towards TMT than towards attractive/neutral odours, such as esters and ketones. Optogenetic modulation of these inhibitory interneurons alters defensive behaviour, confirming the modulation of threat perception. Therefore, we validated the role of the inhibitory network in a pre-cortical stimulus-processing area, namely the olfactory bulb, in regulating innate and learned behavioural decisions and revisions.