Department of Experimental Medicine, Section of Human Physiology and Centro Polifunzionale di Scienze Motorie, University of Genoa, 16126 Genoa, Italy.
J Neurosci. 2011 Mar 2;31(9):3423-8. doi: 10.1523/JNEUROSCI.4893-10.2011.
In the human brain, homologous regions of the primary motor cortices (M1s) are connected through transcallosal fibers. Interhemispheric communication between the two M1s plays a major role in the control of unimanual hand movements, and the strength of this connection seems to be dependent on arm activity. For instance, a lesion in the M1 can induce an increase in the excitability of the intact M1 and an abnormal high inhibitory influence onto the damaged M1. This can be attributable to either the disuse of the affected limb or the overuse of the unaffected one. Here, to directly investigate cortical modifications induced by an abnormal asymmetric use of the two limbs, we studied both the excitability of the two M1s and transcallosal interaction between them in healthy subjects whose right hand was immobilized for 10 h. The left "not-immobilized" arm was completely free to move in one group of participants (G1) and limited in the other one (G2). We found that the non-use reduced the excitability of the left M1 and decreased the inhibitory influence onto the right hemisphere in the two groups. However, an increase in the excitability of right M1 and a deeper inhibitory interaction onto the left hemisphere were evident only in G1. Thus, modifications in the right M1 were not directly produced by the non-use but would depend on the overuse of the "not-immobilized" arm. Our findings suggest that the balance between the two M1s is strongly use dependent.
在人类大脑中，初级运动皮层（M1）的同源区域通过胼胝体纤维连接。两个 M1 之间的半球间通信在手运动的控制中起着主要作用，并且这种连接的强度似乎取决于手臂活动。例如，M1 的损伤会导致未受损 M1 的兴奋性增加，并且对受损 M1 产生异常高的抑制影响。这可能归因于受影响肢体的失用或未受影响肢体的过度使用。在这里，为了直接研究由于两个肢体的异常不对称使用而引起的皮质变化，我们研究了健康受试者的两个 M1 的兴奋性以及它们之间的胼胝体相互作用，这些受试者的右手被固定了 10 小时。在一组参与者（G1）中，左“未固定”手臂完全自由移动，而在另一组（G2）中则受到限制。我们发现，非使用降低了左 M1 的兴奋性，并降低了两个组中对右半球的抑制影响。但是，仅在 G1 中才明显出现右 M1 的兴奋性增加和对左半球的更深抑制相互作用。因此，右 M1 的变化不是由非使用直接产生的，而是取决于“未固定”手臂的过度使用。我们的发现表明，两个 M1 之间的平衡强烈依赖于使用。
