PET ACTIVATION STUDIES OF WORDS

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The major goal of the proposed research is to employ modern functional neuroimaging in normal subjects to characterize brain areas related to specific aspects of language processing. This current proposal narrows the focus from language as a whole to experiments at the level of single words in three areas: 1) experiments designed to identify brain regions involved in rule- based vs. associative memory based language processes. Many recent cognitive psychological studies have focused upon the distinction between language processes which produce transformations using rule-based mechanisms, and those which are based upon stored associations. Many studies, including some of our own work, suggest these different types of processes involve distinct sets of brain regions. Experiments are proposed which address the generality of this dissociation and the extent to which the use of the different types of processes can be experimentally manipulated. 2) experiments designed to explore brain regions to phonological processes. Both lesion-behavior and functional imaging studies have suggested specific correlations between specific brain regions and different phonological processes (including acoustic, articulatory, and word-sound processes). There are currently some intriguing overlaps between studies, as well as some interesting dissociations. The proposed studies will allow us to further explore the nature of the processes involved in different phonological tasks, and to address the different roles played by temporal and frontal regions. 3) to explore specific areas related to semantic processes. Several studies have suggested both left middle temporal and frontal regions may be activated by tasks which include some form of semantic (word meaning) analysis. The proposed experiments build upon previous studies by examining the effect of factors such as the modality of input, the type of semantic information subjects are required to analyze, and how that information is accessed on the activation of brain regions. While this proposal focuses on language processes in normal subjects, the knowledge gained from such studies should be relevant across a wide range of health issues. For example, language impairment is one of the most tragic consequences of stroke, and imaging studies as these may provide information relevant to understanding behavioral deficits. Likewise, a deeper understanding of normal function should provide more targeted rehabilitative strategies in the future. In the broadest sense, studies of normal language function, using all avenues available to us, including functional neuroimaging, should lead to a deeper understanding of the related problems, and to better approaches to their solution.