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J Neurophysiol 97: 738-745, 2007. First published November 8, 2006; doi:10.1152/jn.00773.2006
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Lack of Adaptation to Random Conflicting Force Fields of Variable Magnitude

¹Brain Sciences Center, Veterans Affairs Medical Center, Minneapolis; and ²Graduate Program in Biomedical Engineering and ³Departments of Neuroscience and Neurology, University of Minnesota, Minneapolis, Minnesota

Submitted 26 July 2006; accepted in final form 27 October 2006

The concept of internal models has been used to explain how the brain learns and stores a variety of motor behaviors. A large body of work has shown that conflicting internal models could not be learned simultaneously; this suggests either a limited capacity or the unstable nature of short-term motor memories. However, it has been recently shown that multiple conflicting internal models of motor behavior could be acquired simultaneously if associated with appropriate contextual cues and random presentations. We re-examined this issue in a more complex environment in which the magnitude of the conflicting fields could vary randomly. Human subjects failed to show any evidence of learning the force fields themselves or the magnitude of the forces experienced, even with extended practice. Subjects did adapt to the applied perturbation when the field strength was kept constant but still did not form internal models. Our results show that neither random presentation nor specific contextual cues are sufficient for learning conflicting internal models when the magnitude of the forces is also unpredictable. The data suggest that multiple conflicting internal models cannot be learned in all environments, and provide support for the unstable nature or limited capacity of motor memories.

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				L. E. Brown, E. T. Wilson, M. A. Goodale, and P. L. Gribble Motor Force Field Learning Influences Visual Processing of Target Motion J. Neurosci., September 12, 2007; 27(37): 9975 - 9983. [Abstract] [Full Text] [PDF]