Elsevier

Current Opinion in Neurobiology

Volume 9, Issue 6, 1 December 1999, Pages 735-739
Current Opinion in Neurobiology

Review
Mental imaging of motor activity in humans

https://doi.org/10.1016/S0959-4388(99)00038-0Get rights and content

Abstract

Motor imagery corresponds to a subliminal activation of the motor system, a system that appears to be involved not only in producing movements, but also in imagining actions, recognising tools and learning by observation, as well as in understanding the behaviour of other people. Recent advances in the field include the use of techniques for mapping brain activity and probing cortical excitability, as well as observation of brain lesioned patients during imaging tasks; these advances provide new insights into the covert aspects of motor activity.

Introduction

Motor imagery is now becoming a hot topic in the field of cognitive neuroscience. A major conceptual advance in the past three or four years, which we will discuss in this review, has been to decouple the mental phenomenon of simulating an action from the conscious representation of that action. New methodologies are now being developed where subjects have to go through the process of mental simulation before they can give a response on the feasibility of a movement. Objective cues, such as pattern of responses or response time, can then be correlated with neural events observed during this mental activity.

Section snippets

The two sides of motor imagery: explicit and implicit motor images

Whereas the term ‘motor image’ classically refers to explicit or conscious representation of an action (imagine yourself running or raising your hand), the same concept also includes other, implicit or unconscious, aspects of the same phenomenon. One example of implicit motor imagery is provided by Frak et al. (V Frak, Y Paulignan, M Jeannerod, unpublished data): subjects were shown a glass of water from above with an indication of where the thumb and the index finger should contact it.

How similar are a simulated and an executed action?

This new approach to motor imagery, which focuses on the vehicle (the brain mechanisms involved) rather than on the content of motor images, was critical for retrieving useful results from experiments where the only data were based on subjective reports. If a motor image bears any relationship to the action it simulates, then properties pertaining to the action should be expressed in the image. This similarity is clearly illustrated by results obtained using the mental chronometry paradigm. It

Motor imagery as a subliminal activation of the motor system

The main debate on neural mechanisms of motor imagery now focuses on the degree of involvement of motor pathways, and particularly, primary motor cortex. The most recent studies used either PET or functional magnetic resonance imaging (fMRI) and relate conflicting results. The extensive PET study by Deiber et al. [19••] failed to find a significant activation of primary motor cortex and lateral cerebellum during motor imagery of finger movements. fMRI studies, however, unambiguously demonstrate

Conclusions

Future research on motor imagery should follow two main directions. First, it will be important to determine the exact nature of the subliminal activation of the motor pathways involved in this process, and, more specifically, to determine whether it actually corresponds to an ‘endogenous’ activation of motor structures. This will require a complete description of the state of the motor system, which seems difficult with the presently available techniques. For example, standard EMG recordings

Acknowledgements

The work described here is supported by the Biomed 2 programme.

References and recommended reading

Papers of particular interest, published within the annual period of review, have been highlighted as:

  • • of special interest

  • •• of outstanding interest

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