Acquisition and generalization of visuomotor transformations by nonhuman primates
Exp Brain Res. 2004-10-05; 161(2): 209-219
DOI: 10.1007/s00221-004-2061-4
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Paz R(1), Nathan C, Boraud T, Bergman H, Vaadia E.
Author information:
(1)Interdisciplinary Center for Neural Computation, The Hebrew University,
Jerusalem, Israel.
The kinematics of straight reaching movements can be specified vectorially by
the direction of the movement and its extent. To explore the representation in
the brain of these two properties, psychophysical studies have examined learning
of visuomotor transformations of either rotation or gain and their
generalization. However, the neuronal substrates of such complex learning are
only beginning to be addressed. As an initial step in ensuring the validity of
such investigations, it must be shown that monkeys indeed learn and generalize
visuomotor transformations in the same manner as humans. Here, we analyze
trajectories and velocities of movements as monkeys adapt to either rotational
or gain transformations. We used rotations with different signs and magnitudes,
and gains with different signs, and analyzed transfer of learning to untrained
movements. The results show that monkeys can adapt to both types of
transformation with a time course that resembles human learning. Analysis of the
aftereffects reveals that rotation is learned locally and generalizes poorly to
untrained directions, whereas gain is learned more globally and can be
transferred to other amplitudes. The results lend additional support to the
hypothesis that reaching movements are learned locally but can be easily
rescaled to other magnitudes by scaling the peak velocity. The findings also
indicate that reaching movements in monkeys are planned and executed very
similarly to those in humans. This validates the underlying presumption that
neuronal recordings in primates can help elucidate the mechanisms of motor
learning in particular and motor planning in general.