The adolescent frontal cortex shows stronger population-level encoding of information than the adult during a putative sensitive period

Adolescence is considered to be a sensitive period for brain development, but it is not clear how the neocortex functions differently at this stage. We hypothesized that if there is a sensitive period in the dorsomedial prefrontal cortex (dmPFC) during adolescence, then we might find this area shows stronger encoding of task-related information at adolescent ages than at adult ages. To enable optical access to task-related layer 2/3 neural activity in the developing mouse, we imaged mice under a 2-photon microscope while they learned an auditory go/no-go task. We found adolescent mice (postnatal day P30-45) learned the task to criterion faster than adult mice (P60-75). When we compared neural activity in expert mice with comparable performance between the two age groups, we found that a similar fraction of single cells encoded task variables in the two groups. However, task information could be better decoded from the adolescent dmPFC population activity than the adult, even when we controlled for differences in head-fixed running. Adolescents also showed greater noise correlation than adults, and shuffling to remove this noise correlation suggested noise correlation contributed to gain of function in adolescent compared to adult brain. We suggest a working model for an adolescent sensitive period in the frontal association cortex in which greater capacity for distributed encoding of information in the adolescent dmPFC underlies increased sensitivity to experiences that occur at this stage of life.