Role of the mode of sensory stimulation in presurgical brain mapping in which functional magnetic resonance imaging is used

Object. The aim of this study was to evaluate different types of sensory st imulation used to distinguish between microvasculature and venous drainage on functional magnetic resonance (fMR) images with blood oxygen level-depen dent (BOLD) contrast. Methods. Seven volunteers received three sensory stimulations. One consiste d of small discontinuous automated pokes to the ventral aspect of the right thumbtip. The other two were delivered by the investigator, who vigorously brushed the ventral aspect of the right thumbtip either alone or in combin ation with the thenar region. Seven contiguous axial slices of the head wer e acquired using echoplanar fMR imaging during each mode of stimulation. Bo xcar analysis and Student's t-test were performed. Cluster analysis was use d to determine significant differences between rest and activation phases. The major findings were 1) that a discontinuous sensory stimulation involvi ng a small skin area was able to evoke a limited activated area in the post central gyrus with a low activation index (AI [2%]); 2) that this Limited a ctivated area was included in the activated area elicited by the continuous sensory stimulations; and 3) that this also evoked multiple activated area s exhibiting AIs of either approximately 2% or greater than 5%. This indica ted that the limited discontinuous tactile stimulation evoked a BOLD-contra st fMR image essentially of microvasculature, whereas the more extensive co ntinuous stimulations evoked a BOLD-contrast fMR image in both microvascula ture and venous drainage. Conclusions. Different sensory stimulations are necessary to differentiate primary sensory cortex from venous drainage for presurgical brain mapping.