Neural Correlates of Adolescent Behavior

Adolescence is a developmental stage between childhood and adulthood associated with numerous brain and behavioral changes. It is also a period of vulnerability, as adolescents tend to take more risks, and various psychiatric problems first typically manifest at this time. Yet little is known about the neuronal basis of these vulnerabilities. Although extracellular electrophysiological recording is a useful technique for measuring the neural activity of awake behaving animals, it had not yet been used to address the neural correlates of adolescent motivated behavior. This dissertation therefore had two primary objectives. The first was to characterize a novel behavioral task suitable for testing adolescent and adult rats. The second was to record the neural activity of brain regions involved in motivated behavior, as adolescents and adults performed it. The behavioral task was a simple instrumental learning paradigm, in which rats associated poking into a hole with the delivery of a food pellet reward. While the learning and performance of this task was similar between the two groups, adolescents persisted in this activity more than adults when reward was withheld. It was determined that this was due to different age-related sensitivities to the presence of certain motivational factors.After characterizing the task, it was performed by adolescent and adult rats that had electrode arrays implanted in their orbitofrontal cortex (OFC), nucleus accumbens (NAc), or dorsal striatum (DS). Neural activity was examined in the context of similar instrumental behavior to determine whether adolescents processed salient events in a fundamentally different way from adults. Several interesting neural processing differences were observed, along with some notable similarities. The greatest phasic activity differences were found in the OFC and DS, particularly during the period immediately before reward. Local field potential oscillations also tended to differ, with particular disparities found in the DS. In contrast, NAc activity tended to look similar between adolescents and adults, with a few exceptions. In addition to demonstrating fundamental age-related neural processing differences during motivated behavior, these findings address existing hypotheses and raise new questions relevant to the neural basis of the increased vulnerabilities of adolescence