The effect of movement amplitude on activation in functional magnetic resonance imaging studies

To evaluate the effect of movement amplitude on the "blood oxygen level-dep endent effect," the authors studied six normal subjects while they extended their index finger with two different amplitudes. Images were analyzed usi ng SPM96. In five subjects, the signal intensity increase in the primary se nsorimotor area was significantly greater with the larger amplitude movemen t. In other areas of interest (supplementary motor area, premotor cortex, i nsula, postcentral area, cerebellum), the large-amplitude movement often sh owed significant activation when the small-amplitude movement did not. The authors conclude that, in studies of the motor system, movement amplitude n eeds to be controlled.