Atsuo Waki

To obtain a better understanding of the cortical representation of bimanual coordination, we measured regional cerebral blood flow (rCBF) with 15O-labeled water and positron emission tomography (PET). To detect areas with changes of rCBF during bimanual finger movements of different characteristics, we studied 12 right-handed normal volunteers. A complete session consisted of three rest scans and six scans with acoustically paced (1 Hz) bimanual, mirror, or parallel sequential finger movements. Activation of the right dorsal premotor area (PMd) extending to the posterior supplementary motor area (SMA) was significantly stronger during the parallel movements than during the mirror sequential movements (p < 0.05, at cluster level with correction for multiple comparisons). To determine whether these cortical areas truly represented bimanual coordination, a different group of nine normal volunteers was studied with a different task. Subjects performed acoustically paced (2 Hz) abduction-adduction movements of the index finger, making right only, left only, and bimanual mirror and parallel movements. Activation of the posterior SMA and right PMd was significantly greater during the parallel movements than during the bimanual mirror movements or the unimanual movements of either hand (p < 0.01, with anatomical constraint). Thus, the posterior SMA and right PMd appear to be related to the bimanual coordination of finger movements.

To study neuronal activities that influence the generation of the alpha rhythm, we used positron emission tomography and simultaneous recording of the electroencephalogram (EEG) in normal volunteers and under passive conditions. A negative correlation between regional cerebral blood flow and alpha power was found in the occipital cortex, consistent with the visual modality-specific reactivity of the alpha rhythm. A positive correlation was found in the pons, midbrain, hypothalamus, amygdala, the basal prefrontal cortex, insula and the right dorsal premotor cortex. Neuronal activities of the brain stem and limbic system that are positively correlated with alpha power may provide an anatomical basis for studies of the relationship between emotional state and brain rhythm in health and disease.

The purpose of this study was to investigate the cortical motor areas activated in relation to unilateral complex hand movements of either hand, and the motor area related to motor skill learning. Regional cerebral blood flow (rCBF) was measured in eight right-handed healthy male volunteers using positron emission tomography during a two-ball-rotation task using the right hand, the same task using the left hand and two control tasks. In the two-ball-rotation tasks, subjects were required to rotate the same two iron balls either with the right or left hand. In the control task, they were required to hold two balls in each hand without movement. The primary motor area, premotor area and cerebellum were activated bilaterally with each unilateral hand movement. In contrast, the supplementary motor area proper was activated only by contralateral hand movements. In addition, we found a positive correlation between the rCBF to the premotor area and the degree of improvement in skill during motor task training. The results indicate that complex hand movements are organized bilaterally in the primary motor areas, premotor areas and cerebellum, that functional asymmetry in the motor cortices is not evident during complex finger movements, and that the premotor area may play an important role in motor skill learning.