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Published June 17, 2008 | Published + Supplemental Material
Journal Article Open

Forward estimation of movement state in posterior parietal cortex

Abstract

During goal-directed movements, primates are able to rapidly and accurately control an online trajectory despite substantial delay times incurred in the sensorimotor control loop. To address the problem of large delays, it has been proposed that the brain uses an internal forward model of the arm to estimate current and upcoming states of a movement, which are more useful for rapid online control. To study online control mechanisms in the posterior parietal cortex (PPC), we recorded from single neurons while monkeys performed a joystick task. Neurons encoded the static target direction and the dynamic movement angle of the cursor. The dynamic encoding properties of many movement angle neurons reflected a forward estimate of the state of the cursor that is neither directly available from passive sensory feedback nor compatible with outgoing motor commands and is consistent with PPC serving as a forward model for online sensorimotor control. In addition, we found that the space–time tuning functions of these neurons were largely separable in the angle–time plane, suggesting that they mostly encode straight and approximately instantaneous trajectories.

Additional Information

© 2008 by the National Academy of Sciences of the USA. This contribution is part of the special series of Inaugural Articles by members of the National Academy of Sciences elected on May 3, 2005. Contributed by Richard A. Andersen, March 18, 2008 (sent for review November 16, 2007). We thank R. Bhattacharyya, E. Hwang, I. Kagan, and Z. Nadasdy for comments on the manuscript; K. Pejsa and N. Sammons for animal care; and V. Shcherbatyuk and T. Yao for technical and administrative assistance. This work was supported by the National Eye Institute, the James G. Boswell Foundation, the Defense Advanced Research Projects Agency, and a National Institutes of Health training grant fellowship (to G.H.M.). Author contributions: G.H.M., S.M., and R.A.A. designed research; G.H.M. and S.M. performed research; G.H.M. analyzed data; and G.H.M., S.M., and R.A.A. wrote the paper. The authors declare no conflict of interest. This article contains supporting information online at www.pnas.org/cgi/content/full/0802602105/DCSupplemental.

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