2004 Volume 23 Issue 4 Pages 105-110
The purpose of the present study was to investigate the effect of the repetition rate of a simple movement on the magnitude of neuronal recruitment at maximal effort in humans. Nine right-handed healthy subjects [age: 27.4±4.8 yr, stature: 174.5±12.2 cm, body-weight 74.3±16.6 kg (Mean±SD)] participated in this study. We measured the regional cerebral hemodynamics using 24-channel near infrared spectroscopy (NIRS). An auditory-cued, repetitive flexion movement of the right index finger against a button was performed as the finger-tapping task at maximal effort (ME), at 25% of maximal effort (25% ME) and at 50% of maximal effort (50% ME). The increase of the left primary motor cortex hemodynamics during movement relative to the hemodynamics under the resting condition was calculated for each pair of movement conditions. The frequency of finger-tapping was 1.61±0.18 Hz (25% ME trial), 3.23±0.36 Hz (50% ME trial), and 6.46±0.72 Hz (ME trial). The left primary motor cortex showed significant activation under all conditions. The change in total hemoglobin ([tHb]) between the ME trial and the resting value (1.19±0.93 mmol·mm) was significantly higher than those between the resting value and the 25% ME trial (0.04±0.04 mmol·mm) or the 50% ME trial (0.08±0.11 mmol·mm) (p<0.05). There was a 29.8-fold increase of the [tHb] value between the 50% ME trial and the ME trial, but only a 2-fold increase of the [tHb] value between the 25% ME trial and the 50% ME trial. These results demonstrated that the rate of change in regional cerebral hemoglobin at a maximal effort finger-tapping task was much higher than that at a low frequency finger-tapping task.