Clinical studies We are exploring the role of damage to specific brain areas, including the reward pathways, in the genesis of fatigue, amotivation, and other common, unexplained complaints of military personnel returning from deployment. This study combines intensive neuroimaging with standard and experimental behavioral measures focusing on effort generation. Another study in collaboration with the Naval Medical Research Center and the Walter Reed Army Institute of Research is looking for evidence of behavioral and brain changes in military personnel with occupational exposure to blast. Laboratory studies In a series of experiments, we are using inhibitory transcranial magnetic stimulation to affect activity in the primary motor and dorsolateral profrontal areas, while healthy individuals learn implicit and explicit motor and non-motor information. To date, we have shown that motor cortex inhibition impairs non-motor, as well as motor, implicit learning. This implies that the motor cortex has access to a wider and more general learning network than currently believed. Using functional MRI in conjunction with inhibitory TMS, we have also shown that the deficit in motor learning comes about through subtle shifts in connectivity, rather than a focal, lesion-like, effect at the stimulation site. We are currently completing studies of the effect of prefrontal inhibition on motor and non-motor implicit and explicit learning tasks. Others have shown that TMS directed at a single cortical node in a network involved in visual learning causes a big increase in connectivity within the entire network and correlated improvements in learning. We are investigating this phenomenon in the same network and attempting to expand the concept to the network involved in procedural (practice-based) learning. We hope to apply this to the treatment of memory deficits in patients. Altered synaptic efficacy is an (possibly the) important mechanism of learning and other forms of behavioral adaptation. There are simple and reliable ways of inducing quantifiable changes in behavior, including adaptation to prism goggles that shift vision in the lateral plane. We are studying the basis of this phenomenon with functional MRI and using TMS to intervene in the same neural pathways and attempt to produce the same imaging and behavior changes. Prism adaptation has shown benefits for patients with neglect of the left side of space after stroke. We plan to combine this treatment with TMS in stroke patients to improve visual attention.
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