Event-related fMRI of auditory and visual oddball tasks

Functional magnetic resonance imaging (fMRI) was used to investigate the sp atial distribution of cortical activation in frontal and parietal lobes dur ing auditory and visual oddball tasks in 10 healthy subjects. The purpose o f the study was to compare activation within auditory and visual modalities and identify common patterns of activation across these modalities. Each s ubject was scanned eight times, four times each for the auditory and visual conditions. The tasks consisted of a series of trials presented every 1500 ms of which 4-6% were target trials. Subjects kept a silent count of the n umber of targets detected during each scan. The data were analyzed by corre lating the fMRI signal response of each pixel to a reference hemodynamic re sponse function that modeled expected responses to each target stimulus. Th e auditory and visual targets produced target-related activation in frontal and parietal cortices with high spatial overlap particularly in the middle frontal gyrus and in the anterior cingulate. Similar convergence zones wer e detected in parietal cortex. Temporal differences were detected in the on set of the activation in frontal and parietal areas with an earlier onset i n parietal areas than in the middle frontal areas. Based on consistent find ings with previous event-related oddball tasks, the high degree of spatial overlap in frontal and parietal areas appears to be due to modality indepen dent or amodal processes related to procedural aspects of the tasks that ma y involve memory updating and non-specific response organization. (C) 2000 Elsevier Science inc. All rights reserved.