Previous | Next | To the beginning

Motor preparation revealed by functional imaging

Takashi Nagamine and Hiroshi Shibasaki

Department of Brain Pathophysiology, Kyoto University School of Medicine, Kyoto 606-8507, Japan

Recent developments in functional imaging have enabled investigations of movement related cortical fields (MRCF). Magnetoencephalographic (MEG) studies have disclosed a readiness field (RF), which starts 1 sec prior to a self-paced movement and which is distributed over the precentral gyrus contralateral to the moving side. RF culminates into a motor field (MF), whose generator can be localized into the primary motor cortex. By comparing MRCF with conventional EEG studies, the temporal profile of activation in the crown and fissural part of the precentral gyrus can be estimated separately. When repetitive 2 - Hz finger movements were used, instead of long-interval movements, we have been able to disclose the phasic activation of the somatosensory area, as well as the continuous activity of the motor cortex by the steady-state MRCFs. In addition to these slow field changes, background activity has revealed another temporal feature.

The alpha-band activity, accompanying self-paced movements, starts to dampen in bilateral motor areas 3 - 4 sec prior to the movement, with contralateral predominance. Beta-band activity reveals synchronization after the cessation of movement, as well as dampening prior to the movement. These temporal changes of background activity are observed both for muscle contraction and relaxation, which indicates the common process of preparation for movement initiation and cessation.

By means of event-related functional magnetic resonance imaging (fMRI) better temporal resolution is obtainable, in addition to high spatial resolution. Activated areas related to muscle relaxation can be detected in the precentral gyrus and in the supplementary motor area, which is similar to that for muscle contraction. Combined MEG and fMRI studies enable us to obtain a better understanding of brain mechanisms related to voluntary movement.

Previous | Next