| Human finger movement relies closely on the motor control mechanism of neural system. According to the large hand area projected in the brain motor cortex, it can be deduced that the motor control mechanism is quite complex. Currently, researches about the neural motor control mechanism of human hand include the following aspects such as the cortical oscillation, surface Electromyography (sEMG) and muscle force. In addition to the connection between different motor cortex during voluntary contraction, neural osilations in the primary motor cortex are correlated with muscular activity, and the correlation suggests functional coordination between neural activities and muscle contraction control. Accordingly, it could be of great significance for exploring the control mechanism of voluntary muscle movements by means of corticomuscular coherence analysis.The present work probed into the following preliminary investigations about corticomuscular coordination with Magnetoencephalography (MEG) related to finger force output. First, different finger movement tasks which including self-paced key-press and different force tracking were designed and the force tracking tasks consist of (1) Index finger at 20% maximal voluntary contraction strength (MVC), (2) Index finger at 40% MVC, (3) Combination of index and middle finger at 40% MVC, (4)Index and middle finger in the same force distribution at 40% MVC. And then power spectrum analysis was implemented. Second, the cortical connection change in the time-frequency domain was investigated in the self-paced key-press, and MLC15, which showed strongest activities in the self-paced key-press, was selected as reference channel. Coherence between the reference channel and the rest channels in motor cortex was estimated. Third, corticomuscular coherence (CMC) was measured in the force tracking in order to understand how the motor cortex controls muscle activity during isometric contraction. Finally, comparison of the magnitude of sEMG/Force coherence peak as well as frequency of maximal coherence between different force tracking patterns showed noteworthy observation that the force level had no significant influence on the above two profiles while different finger coordination effect the sEMG/Force coherence significantly.The results about corticomuscular coordination suggested that, (1)Significant increase in CMC amplitude in beta band was associated with increase of force level. It was demonstrated that beta band CMC may serve as an effective sensorimotor integration process through a stronger binding between cortical and motor neurons to stablilize corticospinal communication during isometric compensation of static forces. The increase in alpha band CMC being associated with increase of force level may be caused by the peripheral mechanical oscillation and the central component in 6-15 Hz in physiologic tremor, which reflected a corticomuscular transmission of the oscillation. (2)Beta band CMC varied with the task complexity (i.e., precision of the exerted force), so the difference of the ipsilateral beta band CMC between two different finger coordination models may be associated with the precision during force tracking. (3)Gamma band CMC increase was related to higher task difficulty. This is because difficult task induces ipsilateral and more complex neural activities, and a more complex and continuous intergration of higher attention as well as cognitive information would be needed to modulate gamma band CMC. (4)The modulation of magnitude of sEMG/Force coherence and frequency of maximal coherence was not related to the same neural process in the finger coordination, which represented independent physiological mechanism. Although the physiological basis of CMC has been far from clear, it is now generally accepted that CMC reflects communication between the brain and muscles, which is considered to be related to controlling force.In addition, some suggestive information was obtained through task-related power spectrum analysis and corticocortical coherence analysis. (1) Alpha band ERD shift towards the central and ipsilateral cortex with increase of force level. It could be caused by stronger activities in SMA and ipsilateral motor cortex. (2)Beta band ERD/ERS increase was associated with higher task difficulty. As well known, motor performance improvement is correlated with beta band power spectrum increase. To achieve precise force output in the same force level distribution pattern for index and middle finger, more attention was required to promote the corticospinal communication. (3)More sensorimotor intergration was involed in the complex motor pattern, and gamma band activity was correlated with advanced information processing, which induced oscillations of sensorimotor system shift towards higher frequency. The above inference is still need to be investigated through statistical analysis. |
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