Evidence from neuroimaging studies suggests that the right hemisphere of the human brain might be more specialized for attention than the left hemisphere. However, differences between right and left hemisphere in the magnitude of hemodynamic activity (i.e., 'functional asymmetry') rarely have been explicitly examined in previous neuroimaging studies of attention. This study used a new voxelbased comparison method to examine hemispheric differences in the amplitude of the hemodynamic response in response to infrequent target, infrequent novel, and frequent standard stimuli during an event-related fMRI auditory oddball task in 100 healthy adult participants. Processing of low probability task-relevant target stimuli, or 'oddballs', and low probability task-irrelevant novel stimuli is believed to engage in orienting and attentional processes. It was hypothesized that greater right-hemisphere activation compared to left would be observed to infrequent target and novel stimuli. Consistent with predictions, greater right hemisphere than left frontal, temporal, and parietal lobe activity was observed for target detection and novelty processing. Moreover, asymmetry effects did not differ with respect to age or gender of the participants. The results (1) support the proposal that the right hemisphere is differentially engaged in processing salient stimuli and (2) demonstrate the successful use of a new voxel-based laterality analysis technique for fMRI data.
KeywordsOddball; MRI; Brain; Asymmetry; Cognition Attention is believed to involve a distinctive neural network that interacts with other brain systems to facilitate various cognitive processes. Although there are many different operational definitions of attention, it is generally agreed that attention functions to orient to sensory events, to detect specific signals for subsequent processing, and to maintain vigilance over time (Posner and Petersen, 1990). Previous studies have examined attention by measuring brain activity to target stimuli in the context of 'oddball' tasks. Oddball tasks require detection of infrequent target stimuli within the context of frequently presented standard stimuli (Polich and Kok, 1995;Sutton et al., 1965)-for example, the detection of an occasional high-pitched tone in a sequence of low-pitched tones. The process of detecting salient target stimuli is believed to require orienting and allocation of attention, while vigilance is required to maintain task performance. Brain activity during oddball tasks is frequently measured by averaging taskrelated electroencephalogram recordings to produce event-related potentials (ERPs).
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Author ManuscriptNeuroimage. Author manuscript; available in PMC 2009 October 9.
Published in final edited form as:Neuroimage.
NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript of low probability target stimuli produces a characteristic ERP waveform that includes several meaningful components, including the mismatch negativity (MMN;Naatanen et al., 1992) related t...