Characterizing the brain-behavior basis of habit learning in women with eating disorders
Celone, Kim A.
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This thesis examined brain function in women with eating disorders who meet clinically significant subthreshold DSM-IV criteria for bulimia nervosa (Sub-BN) by investigating the acquisition of motor and cognitive habits. Habit learning is an implicit learning process that is associated with a pattern of parallel processing in fronto-striatal implicit memory system and the medial temporal lobe (MTL) explicit or associative memory system. Neuropsychological and neuroimaging evidence suggest fronto-striatal dysfunction plays a role in the formation and maintenance of maladaptive behaviors and thought patterns in eating disorders. Eighteen Sub-BN and nineteen healthy control women (MC) performed both motor and cognitive habit learning tasks during a single fMRI session. The first experiment examined motor-sequence habit learning via the serial reaction time task (SRTT). The results revealed similar habit learning performance between Sub-BN and healthy control women; however Sub-BN participants demonstrated decreased prefrontal cortex-striatal activation and corresponding MTL increases during habit formation. The second experiment examined regional brain activity during cognitive habit learning on the weather prediction task (WPT), which creates a competing response environment. Findings suggest Sub-BN participants show increased overall caudate nucleus and dorsolateral prefrontal cortex (DLPFC) activation, in addition to initial decreased involvement of the MTL and later increased involvement of the DLPFC. The third experiment utilized functional and effective network connectivity to further explore the data from experiments one and two. The results provide additional support for a disruption in MTL and fronto-striatal memory system interactions, as well as additional disruptions in patterns of "Default Mode Network" and cerebellar connectivity. This thesis demonstrates that during habit learning, disrupted interactions between MTL and fronto-striatal memory systems may be characteristic of the underlying neurobiology of eating disorders. High perfectionism and low self efficacy may result in sensitivity to uncertainty in individuals with eating disorders that alters the adaptive mechanism that controls the utilization of memory systems. In addition, changes in "Default Mode Network" connectivity, as well as increased affective cerebellar connectivity may represent mechanisms that maintain overall beliefs regarding uncertainty. Together, these findings represent viable mediators of the rigid and preoccupying thoughts and behaviors characteristic of individuals with eating disorders.
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