Date

July 2012

Document Type

Dissertation

Degree Name

Ph.D.

Department

Dept. of Behavioral Neuroscience

Institution

Oregon Health & Science University

Abstract

A hallmark of adolescence is dramatic neurodevelopmental and cognitive change. It is also a time when a number of psychological disorders emerge, such as substance abuse and depression, which are accompanied by several features including learning and memory deficits. Thus, it is essential to understand what lifestyle factors influence typical brain development as a means to help foster better prevention and treatment programs for psychopathology during adolescence. Animal and human aging studies suggest that aerobic exercise has beneficial effects on the brain and subsequent learning and memory. However, little research exists on how exercise affects the human adolescent brain. Thus, the goal of this dissertation project was to examine the association between aerobic exercise and learning and memory and its brain basis in human adolescents. I hypothesized that aerobic fitness would relate to larger hippocampal volumes, better learning and memory performance, as well as enhancements in learning-related neural circuitry. To this end, I examined how aerobic fitness related to verbal and spatial learning and memory in 34 male adolescents, ages 15 to 18 years. Furthermore, I collected structural and functional magnetic resonance imaging (MRI) data on this same sample of adolescents to explore how exercise related to hippocampal volume and learning-related neural circuitry. Results showed that aerobic fitness, as measured by VO2 peak, relates to enhanced spatial learning (as measured by performance changes) on a virtual Morris Water Task, as well as larger hippocampal volumes; however, statistical requirements for the hippocampus to mediate the relationship between aerobic fitness and learning were not met. To determine the influence of exercise on neural functioning, brain activity during the encoding of new verbal associative memories was collected and compared between 17 higher (HA) and 17 lower (LA) aerobically active male adolescents. Memory performance was similar on this task between HA and LA youth. During successful memory encoding, both groups activated the left prefrontal cortex and left hippocampus, and showed deactivation of default mode regions. However, compared to HA youth, LA adolescents showed less deactivation in default mode brain regions and also recruited the right prefrontal cortex and hippocampus when encoding information that was later remembered. Taken in the context of the vast literature of normative brain activity seen during memory encoding in adults, I suggest that these results may reflect atypical default mode network function in LA individuals. Furthermore, I argue that the recruitment of right hemisphere homologues (i.e. right prefrontal cortex and hippocampus) may represent a compensatory neural mechanism in LA youth, which may allow for them to obtain similar task performance to their HA peers. Together, these studies suggest that the exogenous factor of aerobic exercise influences spatial learning, hippocampal structure, and the neural basis of memory encoding during adolescence.

Identifier

doi:10.6083/M4NS0RWD

School

School of Medicine

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