| Functional Magnetic Resonance Imaging (fMRI), a non-invasive technique extensively employed for mapping brain function, was used to examine brain activation during language processing and the effect of dopaminergic agents on brain hemodynamics and language. Administration of Levo-Dopa, a drug known to increase levels of dopamine in the brain and used to treat Parkinson's disease, has been associated in behavioral studies with restriction of the semantic network. The current project attempts to identify how these behavioral findings are reflected in brain activation as determined with fMRI. These investigations are summarized in the following.; In the first part of the project, the goal was to determine the effect of L-Dopa on brain hemodynamics. This was motivated by the fact that the fMRI signal is based on cerebral blood flow, oxygenation and cerebral blood volume changes, and any drug administration could interfere with the coupling of neural activation with these parameters, independent of neuronal activity. In order to obtain information about possible global changes in cerebral blood flow (CBF) due to drug administration, a theoretical model of a relationship between the blood oxygenation level dependent (BOLD) signal and CBF was used.; The second part of the project examined the effect of semantic priming on brain activation, and the modulatory effect of dopamine on this type of language processing. The aims of this part of the project were: to implement a protocol for language function imaging, to explore different types of paradigm design in fMRI, and finally to examine the effect of semantic priming on brain activation and the effect of L-Dopa.; Lastly, fMRl was used to study functional connectivity associated with semantic and phonological processing. The goal was to explore the interaction between language network components and to determine if administration of L-dopa would affect this interaction or these types of language processes. During two test sessions (placebo and L-Dopa) each participant performed two fMRI runs, involving phonological and semantic processing of visually presented words. These were used to generate maps of semantic and phonological networks. Activation patterns for the two language processes were obtained and compared to previous findings. |
