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Abstract:
The N-back sequential letter working memory task has been
used to demonstrate load-sensitive activation associated with
maintenance in the dorsolateral prefrontal cortex and transient
load sensitive activation in BrocaUs area. Is this neural substrate
also involved with individual differences in behavioral performance
as difficulty increases? Do these behavioral differences correspond
to increases or decreases in the BOLD response? To address these
questions, in-scanner behavioral data was compared to activation
changes across 90 trials each of the 1-back (1B), 2-back (2B) and
3-back (3B) conditions. Twelve subjects were split into two groups
based on whether their performance deteriorated with increased
memory load (from 1B to 2B, 1B to 3B). 1.5T spiral scans were
movement corrected and co-registered. Those whose performance
deteriorated from 1B to 2B and from 1B to 3B showed increased
activation in the posterior parietal cortex. These preliminary
results are consistent with the view that increased working memory
capacity reflects increased processing efficiency in the brain.
Such studies of individual differences in normal subjects have
important implications for understanding tasks used to evaluate
abnormal populations, such as patients with schizophrenia. Further
work will validate these findings in a second sample.
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