NEUROMAGNETIC ANALYSIS OF THE LATE PHASE OF THE READINESS FIELD FOR PRECISE HAND MOVEMENTS USING MAGNETOENCEPHALOGRAPHY

The aim of this study was to elucidate the cortical regulation of precise finger movements by using magnetoencephalography, with particular emphasis on the late phase of the readiness field. Magnetic brain signals were recorded non-invasively by 306 channel magnetoencephalography during the following two tasks. The first task, a simple task, was to bend the right thumb once as quickly as possible. The second task, a precise one, was to alternately oppose the thumb with the index finger and the middle finger of right hand. In this study, we confirmed that the differences between the two tasks were observed in the late phase of the readiness field, especially in the magnetic field 600 ms before the onset of movement. The activity of the magnetic field of the precise movement task was higher than the activity of the simple movement task. There were obvious differences in the spatial and temporal aspects of the left hemisphere. In the simple movement, the premotor area or motor area was activated in the late phase of the time window. The average latency from the EMG onset was � 98.6� 34.0 ms (n� 5). In the precise movement, the prefrontal area and the SMA were activated in the early and/or middle phases of the time window. The average latency from the EMG onset was � 292.0� 14.9 ms (n� 3) for the prefrontal cortex and � 167.8� 38.3 ms (n� 4) for the SMA. The premotor area or motor area was activated in the late stage of the RF. The average latency from the EMG onset was � 111.6� 61.4 ms (n� 5). Many studies have been performed on the movement-related readiness field. However, the activity of the prefrontal area and the SMA had not previously been studied in the late phase of the readiness field. Our study indicated that the prefrontal area and the SMA played important roles immediately before the onset of precise finger movement. The integration of the prefrontal area, the SMA, and the premotor area is important for the onset of precise finger movement.