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Abstract:
Abstract: For mapping language areas, we have used an fMRI
paradigm wherein a language-processing task was alternated with
"rest." Differences in activation between epochs identified several
putative language areas. However, during rest, subjects' behavior
may activate language-processing areas. Moreover, the
language-processing task likely activates nonlinguistic functional
systems, such as sensory, memory, and attention. Thus, fMR images
of the difference between the language-processing and rest epochs
may not accurately depict language-specific areas. For these
reasons, a nonlinguistic comparison task was developed and is
evaluated here. In the "language" task, subjects silently generated
sentence-length definitions of words presented verbally one every
six seconds. In the nonlinguistic ("tones") task, subjects silently
repeated sequences of three randomly ordered tones presented every
2.5 seconds. During rest subjects concentrated on breathing. Tasks
were performed for 30 sec each in a fixed sequence, repeated four
times. Individual t-tests generated activation maps representing
the differences: language-tones, language-rest, tones-rest. In most
cases, fewer areas of activation were observed for language minus
tones, than were found in language minus rest. Tones minus rest
showed mostly auditory areas of activation. Preliminary analyses
suggest that areas identified by a language-processing task vary
with the comparison task, which emphasizes the need for careful
interpretation of activated regions.
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