随意運動と脳機能の画像化 機能的ＭＲＩを中心に健常者および脳血管障害患者での知見について

Abstract

Functional imaging of the brain is of great value in investigating the mechanisms of motor control and reorganization of motor function after brain damage. Functional magnetic resonance imaging (fMRI) is one of the newer imaging techniques developed. The image contrast of fMRI is generated mainly by regional changes in levels of deoxy-hemoglobin associated with activated neural function. In contrast to positron emission tomography (PET), fMRI allows the study of single subjects without radiation risk and produces images with higher spatial resolution. Moreover, it can be conducted repeatedly. Brain activation observed in studies using fMRI and other techniques such as PET and single photon emission computed tomography depends on various attributes of motor tasks including the rate of performance; the body parts involved; the muscle force exerted; the amplitude during the motor tasks; the method for pacing (externally cued or self-paced) or starting the motions; and the complexity of the task. All of these attributes must be considered to reliably evaluate the results of functional imaging. Although SMC (sensorimotor cortex) activation is generally lateralized, some functional imaging studies showed the activation in ipsilateral SMC with movement of a unilateral hand. This was most pronounced in left hand motion of right-handers and depended on the task complexity. In contrast to the ipsilateral cortical activation, investigators have not yet reached a consensus on the asymmetry in contralateral SMC activation between right- and left-hand motions. The underlying mechanisms of the recovery of motor function following stroke are poorly understood. Some studies with fMRI have investigated the functional reorganization and showed that paretic hand movement produced extended activation in the ipsilateral sensorimotor cortex. This result indicated that the preexisting uncrossed motor pathway might be one of the important components of motor recovery after stroke. Other cortical areas such as the inferior parietal lobe and secondary motor areas have also been suggested to be involved in motor recovery. One study demonstrated that the peri-infarct area played a role in the reorganization of the cortical motor map.