title: Functional diffusion tensor imaging: measuring task-related fractional anisotropy changes in the human brain along white matter tracts.
abstract: BACKGROUND
  Functional neural networks in the human brain can be studied from correlations between activated gray matter regions measured with fMRI. However, while providing important information on gray matter activation, no information is gathered on the co-activity along white matter tracts in neural networks.
  
  
  RESULTS
  We report on a functional diffusion tensor imaging (fDTI) method that measures task-related changes in fractional anisotropy (FA) along white matter tracts. We hypothesize that these fractional anisotropy changes relate to morphological changes of glial cells induced by axonal activity although the exact physiological underpinnings of the measured FA changes remain to be elucidated. As expected, these changes are very small as compared to the physiological noise and a reliable detection of the signal change would require a large number of measurements. However, a substantial increase in signal-to-noise ratio was achieved by pooling the signal over the complete fiber tract. Adopting such a tract-based statistics enabled us to measure the signal within a practically feasible time period. Activation in the sensory thalamocortical tract and optic radiation in eight healthy human subjects was found during tactile and visual stimulation, respectively.
  
  
  CONCLUSIONS
  The results of our experiments indicate that these FA changes may serve as a functional contrast mechanism for white matter. This noninvasive fDTI method may provide a new approach to study functional neural networks in the human brain.
authors.affiliation: Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht, Utrecht, The Netherlands. r.mandl@umcutrecht.nl
authors.forename: René C W
authors.initials: RC
authors.lastname: Mandl
authors.forename: Hugo G
authors.initials: HG
authors.lastname: Schnack
authors.forename: Marcel P
authors.initials: MP
authors.lastname: Zwiers
authors.forename: Arjen
authors.initials: A
authors.lastname: van der Schaaf
authors.forename: René S
authors.initials: RS
authors.lastname: Kahn
authors.forename: Hilleke E
authors.initials: HE
authors.lastname: Hulshoff Pol
mesh_terms: D016880:Anisotropy; D001921:Brain / Q000033:anatomy & histology* / Q000502:physiology; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006801:Humans; D009413:Nerve Fibers, Myelinated / Q000502:physiology*; D009434:Neural Pathways / Q000033:anatomy & histology* / Q000502:physiology; D010775:Photic Stimulation; D011597:Psychomotor Performance; D014110:Touch