J-J. Orban de Xivry: “One perturbation but two different memories: Perturbation statistics modulates the nature of motor memories”
CiNet 1F Conference Rm. A
ICTEAM and IoNS, Université catholique de Louvain, 1200 Brussels, Belgium
When movements are perturbed because of changes in the environment or in the body dynamics, the brain is able to adapt its motor commands in order to maintain motor performance. These perturbations can occur at different time scales (abrupt: walking while carrying a heavy load vs. gradual: walking after having gained weight). Such abrupt and gradual introductions of a perturbation are believed to produce motor memories that differ in strength. Here, we hallenge this assumption and suggest that different perturbation statistics (abrupt vs. gradual) lead to the formation of different motor memories, i.e. motor memories that have different attributes and that rely on a different neural network. First, it is shown that gradual perturbation does not transfer to abrupt perturbation as there was no saving after gradual learning. That is, abrupt but not gradual visuomotor rotation leads to the formation of a model-free motor memory (Huang et al. 2011). Second, it is shown that the motor cortex is reorganized after abrupt but not after gradual perturbation. To assess motor ortex reorganization, the size of motor-evoked potentials (MEPs) was monitored during abrupt and gradual force-field perturbation. These MEPs were modulated by the abrupt but not by the gradual perturbation. In addition, for the abrupt perturbation, the change in MEP was correlated with the strength of the motor memory. Together, the absence of transfer between motor memories formed during abrupt and gradual perturbations and the difference in motor cortex reorganization elicited by these two perturbations statistics suggest that these motor memories are two different entities and not a more or less stabilized version of a unique motor memory.