July 14, 2014 14:00 〜 15:00
CiNet 1F Conference Rm. A
J-J. Orban de Xivry
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 challenge 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 cortex 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.