Letter | Published:

Overlap of internal models in motor cortex for mechanical loads during reaching


A hallmark of the human motor system is its ability to adapt motor patterns for different environmental conditions, such as when a skilled ice-hockey player accurately shoots a puck with or without protective equipment. Each object (stick, shoulder pad, elbow pad) imparts a distinct load upon the limb, and a key problem in motor neuroscience is to understand how the brain controls movement for different mechanical contexts1,2. We addressed this issue by training non-human primates to make reaching movements with and without viscous loads applied to the shoulder and/or elbow joints, and then examined neural representations in primary motor cortex (MI) for each load condition. Even though the shoulder and elbow loads are mechanically independent, we found that some neurons responded to both of these single-joint loads. Furthermore, changes in activity of individual neurons during multi-joint loads could be predicted from their response to subordinate single-joint loads. These findings suggest that neural representations of different mechanical contexts in MI are organized in a highly structured manner that may provide a neural basis for how complex motor behaviour is learned from simpler motor tasks.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1

    Wolpert, D. M. & Ghahramani, Z. Computational principles of movement neuroscience. Nature Neurosci. 3 suppl., 1212–1217 (2000)

  2. 2

    Wolpert, D. M. & Kawato, M. Multiple paired forward and inverse models for motor control. Neural Netw. 11, 1317–1329 (1998)

  3. 3

    Shadmehr, R. & Mussa-Ivaldi, F. A. Adaptive representation of dynamics during learning of a motor task. J. Neurosci. 14, 3208–3224 (1994)

  4. 4

    Kalaska, J. F., Cohen, D. A., Hyde, M. L. & Prud'homme, M. A comparison of movement direction-related versus load direction-related activity in primate motor cortex, using a two-dimensional reaching task. J. Neurosci. 9, 2080–2102 (1989)

  5. 5

    Gandolfo, F., Li, C., Benda, B. J., Schioppa, C. P. & Bizzi, E. Cortical correlates of learning in monkeys adapting to a new dynamical environment. Proc. Natl Acad. Sci. USA 97, 2259–2263 (2000)

  6. 6

    Kalaska, J. F., Scott, S. H., Cisek, P. & Sergio, L. E. Cortical control of reaching movements. Curr. Opin. Neurobiol. 7, 849–859 (1997)

  7. 7

    Porter, R. & Lemon, R. Corticospinal Function and Voluntary Movement (Oxford Univ. Press, Oxford, 1995)

  8. 8

    Ashe, J. Force and the motor cortex. Behav. Brain Res. 87, 255–269 (1997)

  9. 9

    Scott, S. H. Apparatus for measuring and perturbing shoulder and elbow joint positions and torques during reaching. J. Neurosci. Methods 89, 119–127 (1999)

  10. 10

    Scott, S. H., Gribble, P. L., Graham, K. M. & Cabel, D. W. Dissociation between hand motion and population vectors from neural activity in motor cortex. Nature 413, 161–165 (2001)

  11. 11

    Humphrey, D. R. & Reed, D. J. in Motor Control Mechanisms in Health and Disease Advances in Neurology no. 39 (ed. Desmedt, J.) 347–372 (Raven, New York, 1983)

  12. 12

    Fetz, E. E., Cheney, P. D., Mewes, K. & Palmer, S. in Peripheral Control of Posture and Locomotion (eds Allum, J. A. H. & Hulliger, M.) 437–449 (Elsevier, New York, 1989)

  13. 13

    Cabel, D. W., Cisek, P. & Scott, S. H. Neural activity in primary motor cortex related to mechanical loads applied to the shoulder and elbow during a postural task. J. Neurophysiol. 86, 2102–2108 (2001)

  14. 14

    Sanes, J. N. & Schieber, M. H. Orderly somatotopy in primary motor cortex: does it exist? Neuroimage 13, 968–974 (2001)

  15. 15

    McKiernan, B. J., Marcario, J. K., Karrer, J. H. & Cheney, P. D. Corticomotorneuronal postspike effects in shoulder, elbow, wrist, digit, and intrinsic hand muscles during a reach and prehension task. J. Neurophysiol. 80, 1961–1980 (1998)

  16. 16

    Imamizu, H. et al. Human cerebellar activity reflecting an acquired internal model of a new tool. Nature 403, 192–195 (2000)

  17. 17

    Wolpert, D. M., Miall, R. C. & Kawato, M. Internal models in the cerebellum. Trends Cogn. Sci. 2, 338–347 (1998)

  18. 18

    Schmidt, R. A. & Wrisbert, C. A. Motor Learning and Performance: A Problem-Based Learning Approach (Human Kinetics, Champaign, 2000)

  19. 19

    Wightman, D. C. & Lintern, G. Part-task training for tracking and manual control. Hum. Factors 27, 267–283 (1985)

  20. 20

    Scott, S. H. & Kalaska, J. F. Reaching movements with similar hand paths but different arm orientations. I. Activity of individual cells in motor cortex. J. Neurophysiol. 77, 826–852 (1997)

  21. 21

    Gribble, P. L. & Scott, S. H. Method for assessing directional characteristics of non-uniformly sampled neural activity. J. Neurosci. Methods 113, 187–197 (2002)

  22. 22

    Loeb, G. E. & Gans, C. Electromyography for Experimentalists (Univ. Chicago Press, Chicago, 1986)

Download references


We thank K. Moore for technical assistance, and D.W. Cabel and S. Chan who assisted in some of the training and neuronal recording sessions. We thank D. Munoz, M. Pare and K. Rose for comments on this manuscript. This work was supported by a CIHR grant and scholarship (S.H.S.) and a CIHR postdoctoral fellowship (P.L.G.).

Author information

Competing interests

S.H.S. holds a US patent for the robotic device used in these experiments.

Correspondence to Stephen H. Scott.

Supplementary information

Supplementary information, legends to supplementary figures S1 and S2 and references (DOC 49 kb)

Supplementary figure S1 (PDF 123 kb)

Supplementary figure S2 (PDF 34 kb)

Rights and permissions

Reprints and Permissions

About this article

Further reading

Figure 1: Two hypotheses about the neural control of different mechanical loads. A single-controller that encapsulates all load contexts (a), or multiple controllers, each of which represent individual loads (b).
Figure 2: Neural activity of two cells during movement in different dynamic loads.
Figure 3: Changes in cell activity across three load conditions.
Figure 4: Neural representation of mechanically dependent loads.


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.