Masahiro Mikami

Detection of cerebral blood flow changes during repetitive transcranial magnetic stimulation by recording hemoglobin in the brain cortex, just beneath the stimulation coil, with near-infrared spectroscopy.

Many studies measured cerebral blood flow changes in the stimulated primary motor cortex during repetitive transcranial magnetic stimulation (rTMS) using PET, SPECT, and fMRI; however, most of these procedures are associated with problems related to temporal resolution and magnetic field artifacts that are produced by rTMS. In this study of 12 healthy right-handed volunteers, we measured the hemoglobin (Hb) concentration change in the stimulated primary motor cortex during and after rTMS using rTMS coil and near infrared spectroscopy (NIRS) with high temporal sampling (every 125 ms). The left primary motor cortex that controls the right first dorsal interosseus (FDI) muscle was stimulated 10 times with an angle figure-of-eight coil at a frequency of 0.5 or 2 Hz, at intensity of 80% or 120% of resting motor threshold (RMT). We used 4 stimulus conditions: (1) 2 Hz-120% RMT, (2) 2 Hz-80% RMT, (3) 0.5 Hz-120% RMT, and (4) 0.5 Hz-80% RMT. We observed small intensity-dependent increments in total- and oxy-Hb concentrations around 5 s at the 120% RMT condition. Greater decrements in total- and oxy-Hb concentrations and increment of deoxy-Hb concentration were observed during and after rTMS at all conditions, both at the supra-threshold and sub-threshold stimulus intensities. Our results emphasize the suitability of NIRS combined with rTMS for detecting changes in cerebral blood flow.

Activation of supplementary motor area during imaginary movement of phantom toes.

To evaluate changes in the human cerebral cortex after lower limb amputation, we studied repetitive toe movements using functional magnetic resonance imaging. The subject did not experience any phantom pain but had a vivid sensation of the phantom limbs presence and was able to imagine the movement of her phantom toes and ankle. Actual movement of her normal limb activated the contralateral supplementary motor area (SMA), the primary motor cortex (M1), and the primary somatosensory cortex (S1). Movement of her phantom limb activated the contralateral SMA and the M1. Imaginary movement of her normal toes without actual movement activated the contralateral SMA. The slice level that was activated by the movement of the phantom limb was shifted 8 mm caudally, suggesting that cortical reorganization had occurred after the lower limb amputation.