A PARAMETRIC ANALYSIS OF THE RATE EFFECT IN THE SENSORIMOTOR CORTEX -A FUNCTIONAL MAGNETIC-RESONANCE-IMAGING ANALYSIS IN HUMAN-SUBJECTS

We studied the effects of different movement speeds of unimanual right hand movements on functional magnetic resonance signal changes in the sensorimotor cortex using echo planar imaging (EPI). Six healthy righ t-handed subjects were scanned at rest and while executing a finger ta pping task with their right index finger. Movement frequency was visua lly paced at rates ranging from 0.5 to 5 Hz, separated by 0.5 Hz steps . The blood oxygen level dependent (BOLD) response within the left sen sorimotor cortex was linearly and positively related to movement frequ ency. However, this relation holds (r(2) = 0.91) only for movement fre quencies faster than 1 Hz (1.5-5 Hz). For the slower frequencies there was an initial sharp increase of the BOLD response from 0.5 to 1 Hz f ollowed by an activity drop for 1.5 Hz. These results are compatible w ith the idea that two different motor control modes are operative duri ng slow or fast movements. During slow movements a computational deman ding on-line feedback control mode is operative resulting in strong BO LD signals indicating extensive neural activity. During faster movemen ts on the other hand a program-like motor control mode is operative re sulting in less demanding neural computations. The amount of neural co mputation for the latter control mode increases with increasing moveme nt speed. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.