The overall objective of the proposed project is to investigate brain mechanisms during learning in individuals with traumatic brain injury (TBI) with and without clinical depression. Such knowledge can help guide rehabilitation strategies and reduce the burden of TBI. Feedback about the accuracy of one's actions can improve learning by informing an individual whether his/her action is correct or not. Individuals with depression have been shown to have learning deficits and altered brain activity during learning compared to healthy individuals when feedback is presented immediately. Impaired learning through immediate feedback has also been observed in Parkinson's disease (PD) patients. However, PD patients are able to learn from feedback when it is presented after a delay, engaging separate neural mechanisms. Individuals with TBI have also been shown to have learning deficits that are likely exacerbated by depressive symptoms. However, there is no evidence directly examining the neural mechanisms of learning in individuals with TBI with and without depression. The proposed research explores this distinction.
The elucidation of the neural mechanisms associated with learning in individuals with TBI with and without clinical depression will inform 1) scientific knowledge about the effect of depression on the injured brain, 2) TBI interventions about the effectiveness of feedback and its timing, and 3) interventions for other clinical populations that require rehabilitation and have high occurrence of depression. These objectives lie at the heart of the mission of the National Institute of Neurological Disorders and Stroke as they will broaden "fundamental knowledge about the brain and nervous system" associated with learning in TBI and the knowledge gained from fulfilling the above objectives will "reduce the burden" of learning deficits after TBI.
To test these hypotheses, participants will be recruited based on structured clinical interview performed by the team member trained in psychiatric interviewing. Qualified participants will perform an experiment during which they will first study word pairs outside of the functional magnetic resonance imaging scanner. Then, in the scanner, participants will see word pairs again in a multiple-choice format and will have to choose a match for each word. After participants make their choice, feedback will be presented either immediately or after a delay of 25 minutes. The experiment will end with the Test phase, which takes place outside of the scanner, where participants will be presented with the words in the multiple-choice format again so the influence of each feedback type on learning can be evaluated.
Investigators hypothesize that depressed individuals with and without TBI will learn better from delayed compared to immediate feedback, because learning through delayed feedback relies on a different neural mechanism, which is not affected by depression and TBI, compared to learning through immediate feedback. Non-depressed individuals without TBI and clinically depressed individuals without TBI will also be recruited to delineate the influences of depression from the impact of TBI on the brain.
