1. Human Motor Control Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, U.S.A.
2. ^*In Vivo NMR Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, U.S.A.

Correspondence: Mark Hallett, NINDS. NIH, Building 10, Room 5N226, 10 Center Drive, MSC-1428, Bethesda, MD, 20892–1428, U.S.A.

Received 22 February 1999; Revised 5 May 1999; Accepted 6 May 1999.

Abstract

To evaluate the effect of movement amplitude on the "blood oxygen level-dependent effect," the authors studied six normal subjects while they extended their index finger with two different amplitudes. Images were analyzed using SPM96. In five subjects, the signal intensity increase in the primary sensorimotor area was significantly greater with the larger amplitude movement. In other areas of interest (supplementary motor area, premotor cortex, insula, postcentral area, cerebellum), the large-amplitude movement often showed significant activation when the small-amplitude movement did not. The authors conclude that, in studies of the motor system, movement amplitude needs to be controlled.