Shifts in Medial Orbitofrontal Cortex Activity from Adolescence to Adulthood.

Adolescents are characterized by a propensity for risky and impulsive behaviors, likely due to immature frontostriatal circuits. The medial orbitofrontal cortex (MO) is linked to risk and reward prediction during decision-making. Identifying age-dependent differences in MO activity and its inputs to downstream regions can elucidate the neural substrates that permit the transition from high-risk adolescent behaviors to increased risk assessment in adulthood. Action selection biased by information gathered by the MO is likely carried out by efferents into the nucleus accumbens (NAc), which guides reward-directed behaviors. Despite the large age dependency of risk-based decision-making, there is nothing known about adolescent MO activity. Here, we recorded action potentials of MO neurons from anesthetized adult and adolescent rats in vivo. On average, adolescent MO neurons fire faster and within narrower ranges than adults, and adolescents have more active MO neurons than adults. Using antidromic stimulation of axon terminals to identify MO neurons that project to NAc (MO→NAc), we found that adolescent MO→NAc neurons have a narrower range of firing frequencies than non-NAc-projecting MO neurons and adult MO→NAc neurons. These age-dependent differences in MO and MO→NAc populations may result from the fine-tuning of circuits between adolescence and adulthood that promote specific age-dependent behaviors.