Interhemispheric transfer of motor skill tested in a rat model

Abstract

Cross education is occurrence phenomenon discovered at the end of 19th century, whereby unilateral strength training produced an increase in strength of the contralateral homologous muscle group1. Plentiful persuasive evidence exists to support the existence of the cross education not only regarding strength but also for more skillful movements. However, little is known about the precise neural mechanism mediating skill transfer from one side of the body to the other2. Here we use a modified Montoya staircase test to study forelimb skill acquisition and interlimb transfer in Sprague-Dawley rats (only males, weighing approx 300 g at the beginning of the experiment). Rats were housed separately under standard conditions set to a 12h light/12h dark cycle. Rats were on diet until they lost 15% of body weight. Once the body weight was constant ±13g daily chow was provided and water ad libitum. The experiments were carried out according to the ethical guidelines of KU Leuven. First, rats were habituated to the setup for 5 days. Then they were assigned to 3 experimental groups. All groups performed a pre test (day 1), post-test (day 5) and retention test (day 5+7), requiring them to grasp food pellets with both the dominant and non-dominant forepaw. However, the three groups differed regarding their training regime: First, the bimanual training group trained to grasp food pellets with both the dominant and the non-dominant forepaw at day 2-4. Second, the unilateral training groups trained the grasping movement only with the dominant side. Third, the no training group was located in the setup but food pellets were provided such that no grasping action was required. Performance tests as well as motor training was provided twice a day, with one session taking place in the morning and another in the afternoon. Grasping performance was evaluated as the percentage of pellets eaten from all stairs. Preliminary results indicate that rats of the unilateral training group exhibit an impressive amount of transfer to the untrained limb. Future experiments will try to identify which anatomical substrate mediates this effect with transcallosal and cortico-thalamic projections being the major candidate pathways. 1-Scripture EW, Smith TL, Brown EM. On the education of muscular control and power. Studies Yale Psychol Lab 1894;2:114–9. 2-Carroll TJ, Herbert RD, Munn J, et al. Contralateral effects of unilateral strength training: evidence and possible mechanisms. J Appl Physiol 2006;101(5):1514–22.