Post-stimulus response in hemodynamics observed by functional magnetic resonance imaging - difference between the primary sensorimotor area and the supplementary motor area

The blood oxygen level dependency (BOLD) contrast is a useful tool for func tional neuroimaging based on the hemodynamic response to neuronal activatio n. We observed different hemodynamic responses in the BOLD signal between t he primary sensorimotor area (SM1) and the supplementary motor area (SMA) i n the sequential finger movement task. In the SMA, a stronger initial overs hoot and a post-stimulus overshoot were observed. It was hypothesized from the time course analysis that the stronger initial overshoot reflected the activation of the SMA for motor control programming in the initial phase. A lthough the post-stimulus overshoot may be partially explained by cerebral blood flow (CBF) cerebral blood volume (CBV) uncoupling, its mechanism rema ined unknown. In the SM1, only the initial overshoot was observed and the l evel of BOLD signal was almost constant after the initial overshoot during the task period. These observations suggested that the BOLD signal is chara cterized by both CBF-CBV uncoupling and the neuronal activation characteris tics in each region. (C) 2001 Elsevier Science Inc. All rights reserved.