Title: Perceptual decision making and neural encoding of intermittent olfactory stimuli in mice
Abstract
Odor cues from distant objects are sparse and highly fluctuating due to turbulent transport. However, whether animals can exploit these spatiotemporally varying statistics to make effective decisions is unclear. To address this issue, we developed a behavioral task in which head-restrained, water-restricted mice had to make binary decisions based on the total number of discrete odor pulses presented stochastically over 5 seconds, to obtain a water reward. Mouse performance in the task approached saturation when total pulse counts were far from the decision boundary and degraded progressively closer to the boundary. Logistic regression of binary choices against the timing of odor pulses in the breathing cycle revealed that mice gave higher weight to stimuli arriving during inhalation than exhalation, a time dependency that correlated with the magnitude of activity in olfactory sensory neurons. Neural recordings from the Anterior Piriform Cortex of trained animals revealed that 1) neurons fired stochastically upon odor pulse presentation, 2) different neurons could display different levels of tuning to stimulus timing within the respiratory phase, and 3) neuronal population firing can decode task-related variables, but with a timescale that suggests a role in sensory integration rather than in decision-making. Altogether, our study indicates that mice can integrate discrete, intermittent olfactory inputs over several seconds to make decisions, and that the arrival time of olfactory information with respect to breathing cycle modulates its representation across the olfactory pathway, as well as its perceptual weighing. Future directions involve in vivo recordings and perturbation experiments in mouse prefrontal cortex and striatum to study whether brain areas related to the accumulation of evidence from other sensory modalities are also involved in olfactory evidence accumulation.