Changes in neuronal activation with increasing attention demand in healthyvolunteers: An fMRI study

Several lines of evidence suggest that structures involved in mediating att ention differentially respond to increasing processing demand. Investigatio n of differences in neuronal activation, however, has been complicated by m ethodological inconsistencies and concomitant discrepancies in degree of di fficulty and subject effort between disparate tasks. In this study, we util ized fMRI to compare neural activation patterns associated with two related attention tasks associated with different degrees of processing load while controlling for degree of performance difficulty. Healthy volunteers perfo rmed two continuous performance tasks, utilizing an identical pairs paradig m (CPT-IP) and a matched simple number recognition paradigm with degraded s timuli (CPT-DS) during a single fMRI scan. Degree of stimulus resolution de gradation in the latter CPT was designed to equalize degree of performance difficulty between the two tasks. CPT-IP and CPT-DS were both associated wi th activation of frontal, limbic, subcortical, and sensory integratory stru ctures. CPT-IP administration was associated with significantly greater act ivation of left dorsolateral prefrontal cortex, bilateral posterior tempora l cortex, bilateral putamen, and thalamus. This study demonstrates both tha t differing attention tasks are associated with a high degree of functional overlap and that increasing processing demand is associated with increased activation of specific portions of attentional networks. (C) 2001 Wiley-Li ss, Inc.