A cortical basis for perception of internal mechanosensations

Interoception, the sensing of internal bodily signals, is essential for brain-body interactions and shapes emotion, cognition, and behavior1-5. Subconscious internal signals, including heartbeats or stomach fullness, can rise to conscious awareness, and this process can improve with practice. Disrupted interoception is emerging as a common deficit in diverse psychiatric disorders1,3,6,7. Nevertheless, we still lack a fundamental understanding of the neurobiological basis of perception and conscious reporting of internal sensations. Here, we combine genetic access to specific interoceptive primary afferents, with non-invasive optogenetics in mice, to establish a quantitative framework for studying internal perception. Specifically, we developed a behavioral task in which mice report detecting non-invasive optogenetic activation of vagal mechanosensory neurons, establishing "interoceptive psychophysics". We combine this approach with cellular-resolution imaging and manipulations to reveal the neuronal basis for perception of these internal sensations in the interoceptive insular cortex. While representations of sensory stimuli were consistently observed in insular cortex across different tasks, perceptual reports were only encoded during a more difficult psychophysics task, but not during simple detection. Accordingly, manipulations of insular cortex activity revealed that, although it is generally required for behavioral reports of internal signals, it plays an additional role in supporting perception under conditions of uncertainty. These findings reveal a neural basis for perception of internal sensations and provide a blueprint for future quantitative exploration of other interoceptive modalities.