UC San Diego

Plasticity in the brain is required for high order functions such as learning and memory. While sensory representations in the primary cortices were long thought to be fixed, a significant body of work has demonstrated that the primary auditory cortex undergoes a variety of learning-related changes in response to sound-guided tasks. Though many of these changes have been characterized, the function and mechanisms of cortical plasticity remain largely unknown.

Here, we use two-photon calcium imaging to record large populations of neurons in order to address how cortical activity supports associative and non-associative learning. Interestingly, we find that there is a decrease in the representation of behaviorally irrelevant tones, whether these tones are passively presented or served as a non-conditioned tone during discriminative fear learning. This habituation of responses is not due to decreased excitatory drive from the thalamus, but instead an active inhibition resulting from the upregulation of activity of cortical somatostatin-expressing interneurons. This regulation by SOM cells is bidirectional, as assigning behavioral value to a habituated tone subsequently decreases SOM cell activity. In behavior, habituation could serve an important function by allowing for increased discriminability of salient sensory information. Together, these data present an important framework by which the primary auditory cortex gates information according to its behavioral significance, and overall, provides crucial insight into how the brain provides a flexible and effective representation of our sensory landscape.