Facilitation of information processing in the primary somatosensory area in the ball rotation task

Abstract

Somatosensory input to the brain is known to be modulated during voluntary movement. It has been demonstrated that the response in the primary somatosensory cortex (SI) is generally gated during simple movement of the corresponding body part. This study investigated sensorimotor integration in the SI during manual movement using a motor task combining movement complexity and object manipulation. While the amplitude of M20 and M30 generated in the SI showed a significant reduction during manual movement, the subsequent component (M38) was significantly higher in the motor task than in the stationary condition. Especially, that in the ball rotation task showed a significant enhancement compared with those in the ball grasping and stone and paper tasks. Although sensorimotor integration in the SI generally has an inhibitory effect on information processing, here we found facilitation. Since the ball rotation task seems to be increasing the demand for somatosensory information to control the complex movements and operate two balls in the palm, it may have resulted in an enhancement of M38 generated in the SI.

Figure 1

Somatosensory evoked magnetic fields following stimulation of the right median nerve in a subject. (A) The 204-channnel SEF waveforms in a stationary condition viewed from the top of the head. Clear deflections were obtained in the central region contralateral to the side of simulation. (B) An enlarged waveform obtained from one gradiometer channel in the SI (framed channel in A). A vertical line indicates the onset of electrical stimulation. (C) The location of an equivalent current dipole (ECD) in M20 superimposed on the 2D image. The ECD was located in the posterior bank of the central sulcus in the hemisphere contralateral to the simulated side.

Figure 2

Grand averaged waveforms of the superimposed SEFs (10 subjects) in stationary and four motor conditions (A) and topographical maps of M20, M30, and M38 components (B). The artifact following electrical stimulation was eliminated in off-line analysis. The motor tasks were the ball rotation task (BR), the ball grasping task (BG), the air rotation task (AR), and the stone and paper task (SP). In all conditions, the first deflection peaking around 20 ms (M20) following stimulation was observed. While the subsequent component (M30) was clearly identified under the stationary condition, those in the other conditions were decreased. In contrast, especially in the BR task, the component peaking around (M38) increased. Whereas the topographical map of the M20 component was the same in all conditions, that of M38 showed pattern reversal between the stationary condition and BR tasks.

Figure 3

(A) The temporal change of the grand averaged ECD waveforms of the SI (10 subjects) in the stationary and four motor tasks. (A) Whereas the peak amplitude of M30 in four motor tasks decreases with motor tasks compared to the stationary condition, that of M38 enhanced during motor execution. (B) Mean amplitude of the ECD components of the SI. Vertical lines indicate standard deviations. Statistical significance compared with the stationary condition and each component showed that the peak amplitude of the ECD moment for M20 in the BR task was significantly smaller than that in the stationary condition. While, those for M30 in the BR, SP, and AR tasks were significantly smaller than the stationary condition, those for M38 showed a significant enhancement in the same tasks.