PLoS ONE, 2013 · DOI: 10.1371/journal.pone.0076747 · Published: October 17, 2013
In healthy individuals, using one arm strongly can increase the activity in the resting arm. This effect is reduced after spinal cord injury. This study investigated how spinal cord injury affects the connection between the arms at different locations relative to the injury. The research found that in patients with spinal cord injuries, the crossed connection between arms was normal in muscles above the injury, absent in muscles near the injury, and present in muscles far below the injury. Surprisingly, in muscles very far from the injury, this effect was abnormally high. These results suggest that the nerve damage from the injury doesn't spread upwards, and the areas far below the injury have the ability to enhance the remaining connections after a spinal cord injury.
The findings suggest that bilateral motor training strategies in SCI patients should consider the location of the trained muscles relative to the injury site. Muscles distant from the injury may benefit more from crossed corticospinal facilitation.
The aberrant amount of MEP crossed facilitation at distant levels below the injury might offer a new avenue to facilitate corticospinal function.
If the motoneurons of the trained muscle are located at or close to the injury site, benefit less from crossed interactions in the corticospinal pathway will be absent or decreased; whereas in muscles with motoneurons located at a distance from the injury site, where crossed corticospinal facilitation is present or aberrantly increased, additional inputs through facilitatory crossed interactions will be present.