Laboratory studies Others have shown that transcranial magnetic stimulation, a form on of noninvasive brain stimulation, directed at a single cortical node in a network involved in visual learning causes a significant increase in connectivity within the entire network and correlated, clinically relevant, improvements in learning. We have reproduced this effect in the same network and are attempting to apply the concept to the network involved in procedural (practice-based) learning and to enhance the effect by timing the stimulation to the brain electrical rhythm in the network. We are also studying what enhancement of one the visual learning network does to the network involved in practice-based learning. We hope to apply the knowledge gained to the treatment of memory deficits in patients and, possibly, to develop safe ways of temporarily enhancing memory in healthy people involved in critical learning tasks. 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 a few degrees to either side. 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. Recently, we have also shown that prism adaptation changes function of the reward system and affects learning. Others have shown that the reward system in the left hemisphere responds more to reward and system on the right more to punishment. We have been able to increase peoples' behavior to respond a little more to reward than punishment on a simple learning task, by adapting them briefly to prisms which shift visual attention to the left and then cause an increase in visual attention on the right after they are removed. 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. 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.
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