Functional magnetic resonance imaging of language processing and its pharmacological modulation
Functional MRI was used to examine brain activation during language processing and the effect of L-Dopa on brain hemodynamics and language. Firstly, we wished to determine the effect of L-Dopa on brain hemodynamics. Since fMRI signal is based on cerebral blood flow, oxygenation and cerebral blood volume changes, drug administration could interfere with the coupling of neural activation with these parameters, independent of neuronal activity. To obtain this information a theoretical model of a relationship between BOLD signal and CBF was used. The results revealed no significant changes induced by drug in baseline CBF. Therefore, this was not used as a covariate in the subsequent studies of language. Secondly, we examined the semantic priming and dopamine effects on brain activation. We intended to implement a protocol for language function imaging, explore different paradigm designs in fMRI, and examine brain activation and the effect of L-Dopa. Behavioral measurements demonstrated a significant priming effect for all semantic distances. Imaging results showed activation in a network known to be involved in language processing and attention. The block and event related paradigms were explored and compared, revealing the importance of design selection in fMRI. No drug or temporal effects were found on the activation maps, suggesting that more sensitive techniques must be used to detect these changes. Lastly, fMRI 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 they are affected by administration of L-Dopa. Activation patterns for the two language processes were obtained and compared to previous findings. The functional connectivity, calculated as the correlation between the time series data of two brain areas was determined and revealed that language areas were activated more synchronously for phonological tasks than for semantic tasks. No drug effect was found on the activation maps or the functional connectivity results. Our findings could be of significance for patient populations showing atypical levels of dopamine in their brain.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:functional mri brain neuroimaging language semantic priming processing phonological connectivity
Date of Publication:01/01/2006