Examining the equivalence between imagery and execution within the spatial domain \u2013 Does motor imagery account for signal-dependent noise?

James W Roberts,Greg Wood,Caroline J Wakefield

doi:10.1007/s00221-020-05939-z

Abstract

Motor imagery is suggested to be functionally equivalent to physical execution as they each utilise a common neural representation. The present study examined whether motor imagery correspondingly reflects the spatial characteristics of physically executed movements, including the signal-dependent noise that typically manifests in more variable end locations (as indicated by effective target width; We). Participants executed or imagined a single, upper-limb target-directed aim in the horizontal medio-lateral direction. The start and end of the imagined movements were indexed by the lifting and lowering of the limb over the home position, respectively. Following each imagined movement, participants had to additionally estimate their imagined end location relative to the target. All the movements had to be completed at a pre-specified criterion time (400 ms, 600 ms, 800 ms). The results indicated that the We increased following a decrease in movement time for execution, but not imagery. Moreover, the total error of imagined movements was greater than the actual error of executed movements. While motor imagery may comprise a neural representation that also contributes to the execution of movements, it is unable to closely reflect the random sources of variability. This limitation of motor imagery may be attributed to the comparatively limited efferent motor signals.

Highlights

For many years, there has been great interest surrounding motor imagery, where bodily movements are mentally simulated without physically executing the movement itself
Perhaps the most common or accepted theoretical framework surrounding motor imagery involves the concept of functional equivalence, which states that the neural representation that is responsible for the execution of movement is the same as that for the imagery of movement (Jeannerod 1994, 1999)
The present study examined whether the increasing spatial variability that is exhibited following decreases in executed movement times may be reflected in motor imagery

Summary

Introduction

There has been great interest surrounding motor imagery, where bodily movements are mentally simulated without physically executing the movement itself. Perhaps the most common or accepted theoretical framework surrounding motor imagery involves the concept of functional equivalence, which states that the neural representation that is responsible for the execution of movement is the same as that for the imagery of movement (Jeannerod 1994, 1999). This concept has been strongly supported by evidence of imagery and execution correspondingly activating the fronto-parietal neural regions (Filimon et al 2007; Hétu et al 2013). There is evidence that imagery can modulate the corticospinal excitability (e.g., opponense pollicis during imagined forearm extension/flexion) that is generated by transcranial magnetic stimulation at the primary motor cortex (M1) (Fadiga et al 1999)

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