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Differences in the BOLD fMRI response to direct and indirect cortical stimulation in the rat
Author(s) -
Austin V.C.,
Blamire A.M.,
Grieve S.M.,
O'Neill M.J.,
Styles P.,
Matthews P.M.,
Sibson N.R.
Publication year - 2003
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.10428
Subject(s) - stimulation , neuroscience , motor cortex , cortex (anatomy) , haemodynamic response , functional magnetic resonance imaging , cerebral cortex , psychology , chemistry , medicine , heart rate , blood pressure
Functional MRI (fMRI) exploits a relationship between neuronal activity, metabolism, and cerebral blood flow to functionally map the brain. We have developed a model of direct cortical stimulation in the rat that can be combined with fMRI and used to compare the hemodynamic responses to direct and indirect cortical stimulation. Unilateral electrical stimulation of the rat hindpaw motor cortex, via stereotaxically positioned carbon‐fiber electrodes, yielded blood oxygenation level‐dependent (BOLD) fMRI signal changes in both the stimulated and homotypic contralateral motor cortices. The maximal signal intensity change in both cortices was similar (stimulated = 3.7 ± 1.7%; contralateral = 3.2 ± 1.0%), although the response duration in the directly stimulated cortex was significantly longer (48.1 ± 5.7 sec vs. 19.0 ± 5.3 sec). Activation of the contralateral cortex is likely to occur via stimulation of corticocortical pathways, as distinct from direct electrical stimulation, and the response profile is similar to that observed in remote (e.g., forepaw) stimulation fMRI studies. Differences in the neuronal pool activated, or neurovascular mediators released, may account for the more prolonged BOLD response observed in the directly stimulated cortex. This work demonstrates the combination of direct cortical stimulation in the rat with fMRI and thus extends the scope of rodent fMRI into brain regions inaccessible to peripheral stimulation techniques. Magn Reson Med 49:838–847, 2003. © 2003 Wiley‐Liss, Inc.