Sing GC, Joiner WM, Nanayakkara T, Brayanov JB, & Smith MA (2009) Primitives for motor adaptation reflect correlated neural tuning to position and velocity. Neuron, 64:575-89.
Abstract: The motor commands required to control voluntary movements under various environmental conditions
may be formed by adaptively combining a fixed set
of motor primitives. Since this motor output must
contend with state-dependent physical dynamics
during movement, these primitives are thought to
depend on the position and velocity of motion. Using
a recently developed ‘‘error-clamp’’ technique, we
measured the fine temporal structure of changes in
motor output during adaptation. Interestingly, these
measurements reveal that motor primitives echo a key feature of the neural coding of limb motion —
correlated tuning to position and velocity. We show
that this correlated tuning explains why initial stages
of motor learning are often rapid and stereotyped,
whereas later stages are slower and stimulus
specific. With our new understanding of these primitives,
we design dynamic environments that are
intrinsically the easiest or most difficult to learn, suggesting
a theoretical basis for the rational design of
improved procedures for motor training and rehabilitation.