Does the brain model Newton's laws?


How does the nervous system synchronize movements to catch a falling ball? According to one theory, only sensory information is used to estimate time-to-contact (TTC) with an approaching object1,2; alternatively, implicit knowledge about physics may come into play3,4. Here we show that astronauts initiated catching movements earlier in 0 g than in 1 g, which demonstrates that the brain uses an internal model of gravity to supplement sensory information when estimating TTC.

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Figure 1: Test of TTC estimation during ball catching in 0 g.
Figure 2: Anticipatory motor responses during catching in 0 and 1 g.
Figure 3: Timing of forearm rotations and biceps EMG compared to first- and second-order model predictions for different TTC thresholds (λ).


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Support was provided by the French space agency CNES, the Italian space agency ASI and the Italian Ministry of Health. We thank the NASA Flight Research Management Branch, the Lockheed Martin Space Operations Company, the Kinélite development team, the STS-90 astronauts (S. Altman, J. Buckey, A. Dunlap, K. Hire, R. Linnehan, C. Mukai, J. Pawelczyk, R. Searfoss, D. Williams) and M. Venet, A. Lee, D. McMahon, B. Marchiel, M. Pias, and F. Silvagnoli for development of the flight experiment; D. Angelini, M. Ehrette, P. Leboucher, P. Prévost and M. Zaoui for technical assistance; L. Amadio, M. Buderer, A. Guëll, O. Marsal and S. McCollum for program support; and D. Alais, M. Amorim, M. Carrozzo, J. Droulez, R. Grasso, Y. Ivanenko, J. Sanes, P. Senot and I. Viaud-Delmon for comments on the manuscript.

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Correspondence to J. McIntyre or M. Zago.

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McIntyre, J., Zago, M., Berthoz, A. et al. Does the brain model Newton's laws?. Nat Neurosci 4, 693–694 (2001).

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