Effect of stimulus frequency on human cerebral hemodynamic responses to electric median nerve stimulation: a near-infrared spectroscopic study.
We examined the effect of stimulus frequency on optically recorded hemodynamic responses to electric median nerve stimulation. Electric stimuli were delivered to the right median nerve with an intensity of 90% of motor threshold. Four different stimulus frequencies (2, 5, 10, and 20 Hz) were administered in each subject. By means of a multi-channel near-infrared spectroscopic instrument, changes in concentration of oxygenated hemoglobin were continuously measured over the left scalp. After 20 Hz stimulation, we found two spatially and temporally distinct hemodynamic responses. One lasted beyond 60 s, and the center of this response was located over the secondary somatosensory area. The other had a transient duration starting immediately after the stimulus onset and was located in the primary somatosensory hand area. Both responses were linearly augmented as a function of the stimulus frequency. Since temporal activation patterns are different in two somatosensory areas, real-time optical monitoring is necessary in evaluation of hemodynamic responses to electric nerve stimulation.
Tanosaki
Masato
M
Department of Integrated Neuroscience, Tokyo Institute of Psychiatry, 2-1-8 Kamikitazawa, Setagaya-ku, Tokyo 156-8585, Japan. tanosaki-tsk@umin.ac.jp
Sato
Chie
C
Shimada
Miho
M
Iguchi
Yoshinobu
Y
Hoshi
Yoko
Y
D000328:Adult; D000704:Analysis of Variance; D004558:Electric Stimulation / Q000379:methods; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology*; D013003:Somatosensory Cortex / Q000098:blood supply* / Q000502:physiology*; D019265:Spectroscopy, Near-Infrared / Q000379:methods*