Training following unilateral cervical spinal cord injury in rats affects the contralesional forelimb

Rehabilitative training is an essential component of current therapeutic strategies for spinal cord injured individuals. However, there are still various open questions that need to be answered in order to optimize training strategies. For example, why can animals trained in a single task perform worse compared to untrained animals when tested in untrained tasks. Such results suggest a potential competition among motor tasks over spared neuronal circuitry. Whether training induced competition for neuronal circuitry may also exist between injured and spared circuitries of the ipsi- and contralesional extremity is currently unknown. Here we investigated whether training restricted to the frontlimb ipsilateral to cervical spinal injury (IF) can impact motor performance of the contralesional frontlimb (CF) in a rat model of cervical SCI. We compared CF performance following general motor training of all limbs (horizontal ladder), following specific training of the IF (pellet reaching), as well as following a combination of both training paradigms. Our findings indicate that adding ipsilateral side-specific training to general training can negatively impact performance of the CF, without resulting in any improvement of performance of the IF. In conclusion, our results emphasize that important decisions have to be made when designing rehabilitative training strategies, ideally taking into account more than the primarily affected extremity.