Developmental maturation of frontal cortical circuits impacts decision-making

In humans, frontal cortical circuits mature in parallel with the development of higher cognitive functions over the course of 15-20 years. In mice, behavior and brain structure change rapidly until reaching sexual maturity ([~]8 weeks of age). In contrast, the degree to which frontal cortices and the behaviors they support continue to develop in mice after this period is unclear. Here, we uncover age-related changes in the acquisition and execution of a probabilistic reward reinforcement task. Both young and old mice complete a similar number of trials per session, but 16-30-week-old mice obtain higher reward rates than younger mice. The older mice adjust their behavior more readily after failing to receive a reward, suggesting that age-dependent changes to circuits relevant to forming action-outcome associations, such as those in frontal associative cortices (FACs). Indeed, we identified cell-type and input-specific refinements of FAC circuits over the first 24 weeks of age, including protracted reductions in excitatory drive and increases in inhibition onto pyramidal cells. Dampening inhibitory activity in FAC alters behavior in a manner that counteracts the age-related differences. Together, these reveal an extended period of synaptic maturation in FAC that directly impacts age-related changes in decision-making.