Changes of somatosensory evoked potentials during writing with the dominant and non-dominant hands.

Since close attention and special effort are necessary to perform difficult unskilled movements, particular brain activities underlying such movements could be expected to take place in the primary sensori-motor cortices (SI and MI). In this study we focused on such activities by analyzing the difference in the somatosensory evoked potential (SEP) in presence to the electrical stimulation of the median nerve during writing using the dominant and non-dominant hands in twelve right-handed and eight left-handed normal subjects. By alternately stimulating the right and left median nerves during the writing with either hand, SEPs were recorded from both hemispheres. During the dominant hand writing, the middle latency SEP components, i.e., parietal P25 and N33 and frontal N30, were significantly attenuated only in the hemisphere contralateral to the writing hand, corresponding to the conventional gating effect. During the non-dominant hand writing, not only those components recorded from the hemisphere contralateral to the writing hand, but also those from the hemisphere ipsilateral to the writing hand were significantly attenuated. In addition, N20 in the hemisphere contralateral to the writing hand was also significantly attenuated. There was no significant difference in the attenuation between the right-handed and left-handed subjects. The results indicated that the specific interaction between the signals after electrical stimulation and the sensory cortical activities related to the writing using the non-dominant hand occurred in both hemispheres, while it was recognized only in the hemisphere contralateral to the writing hand during the dominant hand writing. We speculate that the somatosensory cortex was more activated and thus interacted with the applied stimulation during the unskilled movement of the non-dominant hand compared to the movement of the dominant hand.