Effect of stimulus rate during median nerve stimulation on bold activity: a 3T fMRI Study

Purpose: Previous findings have shown that the human somatosensory cortical systems that are activated by passive nonpainful electrical stimu- lation include the contralateral primary somatosensory area (SI), bilateral secondary somatosensory area (SII), and bilateral insula. The present study tested the hypothesis that these areas have different sensitivities to stimulation frequency in the condition of passive stimulation. Methods: fMRI was recorded in 8 normal volunteers during nonpainful electrical median nerve stimulations at 1, 3, and 10 Hz repetition rates in separate recording blocks in pseudorandom order. Results: Results of the blood oxygen level-dependent (BOLD) effect showed that the contralateral SI, the bilateral SII, and the bilateral insula were active during these stimulations. As a major finding, only the contralateral SI increased its activation with the increase of the stimulus frequency at the mentioned range. Conclusion: The present method of this study may be useful for presurgical functional mapping of primary somatosensory cortex and for the study of its plastic reorganization following tumor resection or stroke lesions.