title: White versus gray matter: fMRI hemodynamic responses show similar characteristics, but differ in peak amplitude.
abstract: BACKGROUND
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Institute for Biodiagnostics-Atlantic, National Research Council, Halifax, NS B3H 3A7, Canada.
authors.forename: Leanne M
authors.initials: LM
authors.lastname: Fraser
authors.forename: M Tynan
authors.initials: MT
authors.lastname: Stevens
authors.forename: Steven D
authors.initials: SD
authors.lastname: Beyea
authors.forename: Ryan C N
authors.initials: RC
authors.lastname: D'Arcy
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001921:Brain / Q000033:anatomy & histology* / Q000098:blood supply*; D001931:Brain Mapping; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003337:Corpus Callosum / Q000098:blood supply*; D005145:Face; D005260:Female; D007839:Functional Laterality; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D009413:Nerve Fibers, Myelinated; D010100:Oxygen / Q000097:blood; D010775:Photic Stimulation; D013997:Time Factors; D014163:Transfer, Psychology / Q000502:physiology; D014825:Vocabulary; D055815:Young Adult
chemical_list: D010100:Oxygen