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theses

Attention-deficit/hyperactivity disorder (ADHD) poses debilitating impairments in the neurobehavioral systems governing reward learning and processing—key components involved in the control of motivated behaviors. Specifically, ADHD may rely on a system favoring cue-driven habits—rooted in the posterior putamen—over caudate and prefrontal cortex-driven goal-directed behaviors. Impaired motivational control may accompany corticostriatal dysfunction in ADHD (e.g., altered connectivity and striatal recruitment). A comprehensive investigation of habits is necessary to reveal potential motivational control irregularities that may be associated with ADHD. However, although contemporary tools enable the study of habit formation, examining existing habits and their disruption has not garnered comparable interest, necessitating the development of novel methods to capture well-learned habits. This dissertation discusses the neurobehavioral mechanisms of habit formation in ADHD in Study 1, develops a novel Go/NoGo task that capitalizes on existing green-Go and red-NoGo associations to study well-learned habit expression and disruption in Study 2, and applies these new tools to investigate habit expression and disruption as a function of ADHD symptomology in Study 3. In Study 1, despite similarities in behavioral assays of habit formation across groups, adults with ADHD displayed corticostriatal connectivity abnormalities and the hyper-recruitment of the posterior putamen during reward learning, alluding to a neural signature of impaired top-down control. In Study 2, participants exhibited outcome-insensitive habits when managing the Go/NoGo task, in that green-Go and red-NoGo associations elicited impairments in accuracy when incongruent with daily experiences. These habits were broken when participants were provided performance-tracking information paired with extrinsic reward, electing motivational enhancement via feedback as a candidate strategy for restoring goal-directed control. In Study 3, the novel task evoked well-learned habit expression and disruption independent of ADHD symptomology in the general population, although a modest association between hyperactivity and the prepotency to execute well-learned habits was evident. In sum, these studies suggest that ADHD presents corticostriatal abnormalities during motivational control, provide novel tools to better examine well-established habits and their disruption, and highlight the importance of investigating motivational systems in ADHD to better understanding its pathophysiology.

ETD_9910

doi:10.7282/t3-qkcf-vv95

Ph.D.

Includes bibliographical references

ETD doctoral

The author owns the copyright to this work.