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Blood oxygenation dependent contrast (BOLD) fMRI is used increasingly to probe "connectivity" based on temporal correlations between signals from different brain regions. This approach assumes that there is constant local coupling of neuronal activity to the associated BOLD response. Here we test the alternative hypothesis that there is not a fixed relationship between these by determining whether attention modulates apparent neurovascular coupling. Electrical stimulation of the median nerve was applied with and without a concurrent distractor task (serial subtraction). Increasing stimulation intensity increased discomfort ratings ( p<0.001) and was associated with a significant increase in both somatosensory evoked potential (SEP) N20-P25 amplitude and BOLD fMRI response in the contralateral primary (SI) and bilaterally in the secondary somatosensory cortices. Attention to stimulation was reduced during distractor task performance and resulted in an overall trend for reduction in discomfort ( p=0.056), which was significant at the highest stimulation level ( p<0.05). A volume of interest analysis confined to SI confirmed a reduction in BOLD response with distraction ( p<0.001). However, distraction did not measurably affect SEP magnitude. The quantitative relationship between the BOLD fMRI response and the local field potential measured by the early SEP response therefore varies with attentional context. This may be a consequence of differences in either local spatial or temporal signal summation for the two methods. Either interpretation suggests caution in assuming a simple, fixed relationship between local BOLD changes and related electrophysiological activity.

Original publication

DOI

10.1007/s00221-003-1827-4

Type

Journal article

Journal

Exp Brain Res

Publication Date

08/2004

Volume

157

Pages

269 - 274

Keywords

Adult, Afferent Pathways, Attention, Brain Mapping, Cerebrovascular Circulation, Electric Stimulation, Evoked Potentials, Somatosensory, Female, Functional Laterality, Humans, Magnetic Resonance Imaging, Male, Median Nerve, Neural Conduction, Neuropsychological Tests, Psychomotor Performance, Somatosensory Cortex