Reorganization during Stroke Recovery monitored by fMRI and SPECT Recovery of lost function after stroke is highly variable among stroke patients, and can probably be attributed to two mechanisms: (a) recovery of undamaged but temporarily "stunned" brain tissue normally involved in the lost function, and (b) recruitment of non-involved areas to take on functions previously performed by damaged brain tissue. Better understanding of the roles of these mechanisms could lead to better prognoses and to improved treatment choices for stroke. The project will use motor and cognitive activation tasks during dynamic Xenon Single Photon Emission Computed Tomography (SPECT) and fMR imaging to assess the extent to which recovery from stroke depends on restitution of function in temporarily impaired cerebral tissue versus recruitment of unaffected brain areas previously uninvolved in the lost function. Functional motor and cognitive tasks are used. Quantitative blood flow imaging during rest and CO2 stress will help localize low flow areas Initial results obtained in six patients studied 6 to 12 months post stroke provide evidence that compensatory changes occur in the undamaged hemisphere during recovery from unilateral stroke [G. Deutsch et al., submitted to Fourth International Conference on Functional Mapping of the Human Brain, Montreal, June 1988]. In comparison with previous investigations, this project offers a more comprehensive approach to evaluating plasticity and reorganization in stroke recovery because it provides a model and techniques that take into account local and distant brain activity impairments and changes in these impairments. The improved understanding of stroke recovery mechanisms afforded by this project should lead to improvements in accuracy of prognosis and choices of treatment, and techniques developed in the project should lead to more effective neuroimaging protocols for evaluation of stroke and stroke recovery.