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Does hypercapnia-induced cerebral vasodilation modulate the hemodynamic response to neural activation?
D R Corfield1, K Murphy, O Josephs
1Wellcome Department of Cognitive Neurology, Institute of Neurology, London WC1 3BG, United Kingdom.
Neuroimage
|May 16, 2001
Summary
Vasoactive agents increase cerebral blood flow and blood oxygen level-dependent (BOLD) MRI signals. This study found that the effects of vasodilation and neural activation on BOLD MRI signals are simply additive, not complexly interactive.
Area of Science:
- Neuroimaging
- Physiology
- Magnetic Resonance Imaging
Background:
- Cerebral blood flow (CBF) changes influence blood oxygen level-dependent (BOLD) MRI signals.
- The interaction between vasoactive-induced vasodilation and activation-related BOLD signal changes is not fully understood.
Purpose of the Study:
- To investigate whether vasodilation and neural activation have additive or complex interactive effects on BOLD MRI signal changes.
- To characterize the relationship between hypercapnia-induced vasodilation and visually evoked BOLD responses.
Main Methods:
- BOLD MRI was performed on four healthy male subjects using T2*-weighted echo planar imaging at 2 Tesla.
- Subjects underwent periods of visual stimulation (flickering checkerboard) and hypercapnia (4% inspired CO(2)).
- Data analysis was conducted using SPM96 to assess signal changes and interactions.
Main Results:
- Hypercapnia, inducing a 25-40% increase in CBF, caused widespread significant BOLD signal increases, primarily in grey matter.
- Visual stimulation elicited significant BOLD signal changes in the occipital cortex.
- No significant interactions were found between hypercapnia-induced vasodilation and visual stimulation-induced signal changes in the occipital cortex.
Conclusions:
- The effects of physiological levels of vasodilation on activation-related BOLD MRI signal changes are simply additive.
- This finding has implications for interpreting BOLD fMRI studies, particularly those involving manipulations of CO(2) or other vasoactive stimuli.