Differences in functional magnetic resonance imaging of sensorimotor cortex during static and dynamic finger flexion

Functional magnetic resonance imaging (fMRI) studies of the human motor sys tem have commonly used movement paradigms which contain a dynamic component ; however, the relationship between the fMRI signal for motor tasks with an d without a dynamic component is not known. We have investigated the relati onship between the fMRI signal during a static finger flexion task and duri ng dynamic finger flexion at 1-3 Hz, each at two levels of force (5% and 10 % of maximum voluntary contraction). A small fMRI response could be recorde d from only a few subjects during the static tasks. In contrast, a substant ial fMRI response occurred during dynamic tasks in all subjects at both lev els of force. The fMRI response was not significantly correlated with force or movement rate during the dynamic tasks. It is concluded that the factor s responsible for generating an fMRI response are fundamentally different d uring steady contractions compared to those involving a dynamic component, and that the fMRI signal may be more sensitive to changes in the pattern of neural activation rather than the ongoing firing rate or extent of activat ion.