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Differences in the hemodynamic response to event-related motor and visual paradigms as measured by near-infrared spectroscopySeveral current brain imaging techniques rest on the assumption of a tight coupling between neural activity and hemodynamic response. The nature of this neurovascular coupling, however, is not completely understood. There is some evidence for a decoupling of these processes at the onset of neural activity, which manifests itself as a momentary increase in the relative concentration of deoxyhemoglobin (HbR). The existence of this early component of the hemodynamic response function, however, is controversial, as it is inconsistently found. Near infrared spectroscopy (NIRS) allows quantification of levels of oxyhemoglobin (HbO(2)) and HbR during task performance in humans. We acquired NIRS data during performance of simple motor and visual tasks, using rapid-presentation event-related paradigms. Our results demonstrate that rapid, event-related NIRS can provide robust estimates of the hemodynamic response without artifacts due to low-frequency signal components, unlike data from blocked designs. In both the motor and visual data the onset of the increase in HbO(2) occurs before HbR decreases, and there is a poststimulus undershoot. Our results also show that total blood volume (HbT) drops before HbO(2) and undershoots baseline, raising a new issue for neurovascular models. We did not find early deoxygenation in the motor data using physiologically plausible values for the differential pathlength factor, but did find one in the visual data. We suggest that this difference, which is consistent with functional magnetic resonance imaging (fMRI) data, may be attributable to different capillary transit times in these cortices.
Document ID
20040087505
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Jasdzewski, G.
(Massachusetts General Hospital, Harvard Medical School 149 13th St., Charlestown, MA 02129, United States)
Strangman, G.
Wagner, J.
Kwong, K. K.
Poldrack, R. A.
Boas, D. A.
Sutton, J. P.
Date Acquired
August 21, 2013
Publication Date
September 1, 2003
Publication Information
Publication: NeuroImage
Volume: 20
Issue: 1
ISSN: 1053-8119
Subject Category
Life Sciences (General)
Funding Number(s)
CONTRACT_GRANT: P41-RR14075
CONTRACT_GRANT: R29-NS38842
Distribution Limits
Public
Copyright
Other
Keywords
NASA Program Biomedical Research and Countermeasures
Non-NASA Center
NASA Discipline Life Sciences Technologies
Clinical Trial

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