5. F-wave by different methods of motor imagery with isometric opponens pollicis activity

Abstract

Our aim of this study was to investigate how transcranial magnetic stimulations (TMS) affect the spinal motoneuron excitability as measured by the amplitude of F-waves in the first dorsal interosseous muscle. Seven healthy subjects took part in the study. The effects of TMS were examined using a conditioning-test paradigm. Conditioning pulses of magnetic stimulation were delivered over motor cortex, prefrontal cortex, parietal cortex or cervical root, at various inter-stimulus intervals (ISIs, 5–300 ms) with the subjects at rest; Test electrical stimuli were delivered to the ulnar nerve to evoke an F-wave. The conditioning stimuli over motor cortex significantly increased the peak amplitude of F-wave with either 5–20 or 165–220 ms ISI. The conditioning stimuli over prefrontal cortex significantly increased the F-wave amplitude with either 85–120 or 225–240 ms ISI. The conditioning stimuli over parietal cortex produced little effect on the F-wave. The conditioning stimuli over cervical root increased the F-wave amplitude with 125–300 ms ISI. The facilitation of F-wave by the motor cortex stimulation might result from the activation of corticospinal output or the afferent feedback due to muscle twitch. The facilitation of F-wave by the prefrontal stimulation might have a non-corticospinal origin.