Thursday, December 18, 2008

images and execution

"Motor Imagery", Journal of Physiology - Paris (2006) by Martin Lotze and Ulrike Halsband
Part 1 (pp 386-389)

The initial section of this article is essentially a review of the recent literature on motor imagery.

Concerning the primary motor cortex:
Several non-music-related studies show activation in the primary motor cortex (cM1), which is usually thought to be purely execution-al, when subjects imagine activities. Interestingly, there is no involvement of the cM1 in a study in which musicians perform music mentally, suggesting that subjects who frequently train with imaging techniques (such as musicians) either activate the cM1 too quickly to register or not at all.
All of the recent research concerning the cM1 and mental imagery seems to indicate that while the primary motor cortex is involved in motor imagery, it is not essential.

Concerning the cerebellum:
Cerebellar activations are highly correlated with activations of the sensorimortor cortex and it seems that areas distinct from those activated during movement execution are activated during mental imagery.

Concerning the supplementary motor area:
The posterior supplementary motor area and the premotor cortex are both consistently reported to be activated in all motor imaging studies, indicating that the preparation for movement may be closely related to motor imagery.

Concerning the premotor cortex:
It seems that while both the dorsal and ventral parts of the premotor cortex are involved with mental imagery, the dorsal part is activated in relation to somatosensory imagination while the ventral parts are activated more through visual imagination.

Concerning the superior parietal lobe:
Parietal activation does not usually happen when subjects imagine simple movements. Studies show that activation occurs during mental imagery of activities with higher spatial aspects, leading to the conclusion that the parietal lobe is important for mental imagery training in patients, musicians and athletes. Especially in regard to the coding for spatial qualities of movement and to the access of the storage of the movement trajectory information.

Some conclusions:
  • Visual imagery and motor (or kinesthetic) imagery show different qualities and therefore must be differentiated in studies
  • Imagery quality (or subjects' perception of it) must be controlled as closely as possible
  • Easily performed movement executions are often too fast to imagine for subjects who do not regularly use mental imagery, so frequencies with half the velocity of regular movement should be used
  • Subjects who train using mental imagery techniques (athletes, musicians, etc.) may use images of higher frequency
  • Not only frequency, but the force required for the kinesthetic image must be controlled (mental effort for mental imagery is force dependent)


This is a densely written article that took a fair amount of research on my part to fully understand everything it discusses. Of course, the article is the perfect introduction to one of the areas of my essay, as it gives an overview of the recent research concerning motor imagery and refers to a number of other studies that are also relevant to my essay topic. The main thing I learned from this article is not so much how the brain works but how (a very small portion of) the brain seems to be 'mapped' in terms of motor imagery. (In other words, which parts of the brain are activated during certain activities.) The mapping of the brain is not quite as interesting to me as the function of the brain but some of the insights gained and conclusions drawn from what is essentially 'mapping research' are applicable to the function of the brain.

by Shannon Coates

No comments: