Pupillometry signatures of neural activity and serotonin release within the auditory cortex of behaving mice

Abstract

The auditory cortex receives bottom-up sensory inputs and top-down neuromodulatory inputs that convey information about behavioral states, such as arousal, attention, and reward acquisition. Therefore, the auditory cortex is uniquely positioned to integrate sensory and behavioral signals. Indeed, behavioral states have been shown to modulate the activity of auditory cortical neurons as well as performance in behavioral auditory tasks. However, the mechanisms by which these states modulate auditory behavioral performance are not yet fully understood. To answer these questions, optical fibers were implanted into the primary auditory cortex (A1) of adult mice. Mice were head-fixed in an operant chamber, where two cohorts of mice were trained on two distinct auditory behavioral tasks, one assessing perceptual discrimination and the other associative learning. We performed in-vivo fiber photometry imaging of bulk fluorescence activity, measuring changes in the fluorescent signals from either a calcium indicator (GCaMP6s) to measure neuronal activity or a serotonin (5-HT) sensor (GRAB-5HT) to measure serotonin release. This was done while simultaneously recording pupil size and whisker motion data as measures of animal behavioral state using infrared video. We observed that behavioral states correlate with activity within A1 and reflect performance during auditory discrimination tasks. We found that performance was best at arousal states when pupil size was neutral or slightly constricted. Furthermore, pupil size correlated closely with excitatory pyramidal neuron activity within A1. Auditory associative learning was associated with an increase in 5-HT release in A1, and ongoing work is determining how this 5-HT release correlates with arousal, as measured using pupillometry. Understanding how behavioral states and neuromodulation affect A1 will further elucidate the mechanisms underlying auditory perception and behavioral performance