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Dynamic cortical activity in the human brain reveals motor equivalence

Abstract

That animals and humans can accomplish the same goal using different effectors and different goals using the same effectors attests to the remarkable flexibility of the central nervous system. This phenomenon has been termed ‘motor equivalence’1,2, an example being the writing of a name with a pencil held between the toes or teeth. The idea of motor equivalence has reappeared because single-cell studies in monkeys have shown that parameters of voluntary movement (such as direction) may be specified in the brain, relegating muscle activation to spinal interneuronal systems3,4. Using a novel experimental paradigm5 and a full-head SQUID (for superconducting quantum interference device) array to record magnetic fields corresponding to ongoing brain activity, we demonstrate: (1), a robust relationship between time-dependent activity in sensorimotor cortex and movement velocity, independent of explicit task requirements; and (2) neural activations that are specific to task demands alone. It appears, therefore, that signatures of motor equivalence in humans may be found in dynamic patterns of cortical activity.

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Figure 1: Relative phase across cycles for all conditions (top row, synchronization; bottom row, syncopation) and all subjects, a total of 500 observations per condition.
Figure 2: Neuromagnetic activity of the human brain.
Figure 3: Cortical activity patterns for each experimental condition.
Figure 4: Relationship between cortical activity and movement velocity.
Figure 5: Brain activity fields for the four conditions in the first experiment, flexion and extension movements at 1 Hz, after the dominant spatial pattern (shown in Fig. 4b) was removed from the data set.

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Acknowledgements

This research was supported by NIMH (U.S.A.), NSERC (Canada) and the Human Frontier Sciences Program. We thank M. Burbank and J. Vrba for the use of facilities at Port Coquitlam, British Columbia.

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Correspondence to J. A. S. Kelso.

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Kelso, J., Fuchs, A., Lancaster, R. et al. Dynamic cortical activity in the human brain reveals motor equivalence. Nature 392, 814–818 (1998). https://doi.org/10.1038/33922

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