White versus gray matter: fMRI hemodynamic responses show similar characteristics, but differ in peak amplitude
1 Institute for Biodiagnostics (Atlantic), National Research Council, Halifax, NS, B3H 3A7, Canada
2 Department of Psychology/Neuroscience, Dalhousie University, Halifax, Canada
3 Department of Physics and Atmospheric Sciences, Dalhousie University, Halifax, Canada
4 Department of Radiology, Dalhousie University, Halifax, Canada
5 School of Biomedical Engineering, Dalhousie University, Halifax, Canada
6 Department of Anatomy and Neurobiology, Dalhousie University, Halifax, Canada
BMC Neuroscience 2012, 13:91 doi:10.1186/1471-2202-13-91Published: 1 August 2012
There is growing evidence for the idea of fMRI activation in white matter. In the current study, we compared hemodynamic response functions (HRF) in white matter and gray matter using 4 T fMRI. White matter fMRI activation was elicited in the isthmus of the corpus callosum at both the group and individual levels (using an established interhemispheric transfer task). Callosal HRFs were compared to HRFs from cingulate and parietal activation.
Examination of the raw HRF revealed similar overall response characteristics. Finite impulse response modeling confirmed that the WM HRF characteristics were comparable to those of the GM HRF, but had significantly decreased peak response amplitudes.
Overall, the results matched a priori expectations of smaller HRF responses in white matter due to the relative drop in cerebral blood flow (CBF) and cerebral blood volume (CBV). Importantly, the findings demonstrate that despite lower CBF and CBV, white matter fMRI activation remained within detectable ranges at 4 T.