Motor learning of new force fields has been examined to explore how the
nervous system may modify sensory-to-motor transformations. When the
kinematics of limb movement are perturbed by altered force environments,
somatosensory as well as visual error signals may drive adaptive update of
the motor commands. It has been suggested that proprioceptive (rather than
visual) information is critical to update internal models of limb dynamics.
Consistent with this view, DiZio and Lackner (2000) reported that blind
subjects can adapt their goal-directed arm movements as well as sighted
subjects, when moving in a new force field. However, recently our group
found that vision may in fact contribute to dynamic adaptation, presumably
via its integration with proprioception (Bourdin et al. 2006). In the
present study, we assessed how a deafferented patient, totally deprived of
proprioception, adapted to a novel force environment as compared to healthy
controls. Subjects were required to point toward visual targets while seated
at the center of a rotating platform producing a new force field.
Surprisingly, we found that the deafferented patient adapted as efficiently
as controls. This highlights the flexibility of the central nervous system
which can use information from different sensory modalities to achieve
identical adaptation outcomes.