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Article Excerpt
Task performance and brain function during fMRI scanning is assumed to be similar to that in everyday settings. However, previous research suggests that language task performance can be affected by competing stimuli in persons with aphasia. To investigate the effect of the intense noise accompanying MRI scanning on language processing, participants with aphasia and control subjects completed two language tasks in three noise backgrounds--silence, sparse scanner noise, and continuous scanner noise. The results of these mock-scanning sessions indicated only small influences of the scanning noise on performance of both groups. However, aphasic individuals having poorer auditory comprehension were more affected by continuous, but not sparse, scanner noise. These findings suggest that future fMRI studies of aphasic individuals might be improved by using sparse rather than continuous scanning techniques.
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The use of functional magnetic resonance imaging (fMRI) in the investigation of language impairment (aphasia) following stroke has increased significantly over recent years. In any study of brain-behavior relationships using fMRI, there is an implicit assumption that subjects' task performance in the MRI scanner must be comparable to that of a more "natural" testing environment. That is, we expect that the observer will behave essentially the same and that the brain will respond similarly outside of the scanner, compared to inside. However, the MRI scanning environment has a number of unusual attributes, most notably, the continuous loud noise.
Work involving neurologically intact individuals has shown that this noise can have a variety of effects. It may itself serve as an acoustic stimulus capable of producing activation of the auditory cortex (Bandettini, Jesmanowicz, Van Kylen, Birn, & Hyde, 1998; Bilecen, Radu, & Scheffler, 1998; Hall et al., 2000; Shah, Jancke, Grosse-Ruyken, & Muller-Gartner, 1999). While some investigators have suggested the utility of this activation in routine clinical examination (e.g., Bilecen et al., 1998), others have examined its time-course in an attempt to mitigate its ability to obscure activation resulting from other stimuli of interest (e.g., Hall et al., 2000; Shah et al., 1999). The interested reader is directed to Amaro et al. (2002) and to Moelker and Pattynama (2003) for comprehensive reviews of these topics.
Clearly, scanner noise may have a detrimental effect on the cognitive performance of all subjects. Attempting to understand the differences in brain function between healthy adults and neuropsychological patients using functional imaging requires appreciating whether aspects of the scanner environment (especially the intense scanner noise) have a differentially detrimental effect on behavioral response in persons with stroke compared to their normal counterparts.
A number of studies suggest that scanner noise may affect persons with aphasia (PWA) more than control subjects because of impaired attentional processing and exaggerated susceptibility to auditory distraction. For example, Tseng, McNeil, and Milenkovic (1993) found impaired attention allocation in aphasic persons during semantic and phonetic target detection. Also in aphasic persons, Murray, Holland, and Beeson (1997) found the presentation of competing pure tones or secondary language stimuli to adversely affect auditory comprehension during focused and divided attention conditions. Similarly, an investigation of spoken language by PWA revealed fewer utterances produced in a divided attention condition compared to isolation; this decrement was greater than that seen in normal control subjects (Murray, Holland, & Beeson, 1998). Again, using pure tones as competing stimuli, Murray (2000) demonstrated a significantly greater decrease in word retrieval and pure tone discrimination by aphasic persons compared to normal controls on both focused and divided attention tasks. Indeed, McNeil (1997) has argued that impairment in the allocation of attention exacerbates the effect of language impairment in aphasia and, therefore, should be...
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