Elsevier

Human Movement Science

Volume 24, Issues 5–6, October–December 2005, Pages 644-656
Human Movement Science

Premovement activity of the pre-supplementary motor area and the readiness for action: Studies of time-resolved event-related functional MRI

https://doi.org/10.1016/j.humov.2005.10.001Get rights and content

Abstract

The supplementary motor area (SMA) is thought to play in important role in the preparation and organisation of voluntary movement. It has long been known that cortical activity begins to increase up to 2 s prior to voluntary self-initiated movement. This increasing premovement activity measured in EEG is known as the Bereitschaftspotential or readiness potential. Modern functional brain imaging methods, using event-related and time-resolved functional MRI techniques, are beginning to reveal the role of the SMA, and in particular the more anterior pre-SMA, in premovement activity associated with the readiness for action. In this paper we review recent studies using event-related time-resolved fMRI methods to examine the time-course of activation changes within the SMA throughout the preparation, readiness and execution of action. These studies suggest that the pre-SMA plays a common role in encoding or representing actions prior to our own voluntary self-initiated movements, during motor imagery, and from the observation of others’ actions. We suggest that the pre-SMA generates and encodes motor representations which are then maintained in readiness for action.

Section snippets

The supplementary motor area

The supplementary motor area (SMA) lies on the mesial surface of each cerebral hemisphere, within the interhemispheric fissure, immediately anterior to the primary motor cortex. It has reciprocal connections with many cortical and subcortical areas and participates within re-entrant circuits involving the motor cortex, the basal ganglia, and the cerebellum which interact in the control of movement. The SMA is generally thought to play an important role in the higher order organisation and

Premovement activity: The Bereitschaftspotential

It is 40 years since Lueder Deecke and Hans Helmut Kornhuber first reported the slow negative potential shift in EEG activity preceding voluntary movement which they termed the Bereitschaftspotential or readiness potential (Kornhuber & Deecke, 1965). The Bereitschaftspotential represents increasing premovement activity thought to underlie the preparation and readiness for action. Since its discovery, much significance has been attached to the readiness potential, from studies of movement

Functional brain imaging: methods

Brain imaging methods such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) provide far greater spatial resolution than surface-EEG for accurately localising activity sources. These techniques, however, provide poor temporal resolution because they rely on detecting changes in blood flow which are slow and delayed relative to the underlying changes in neural activity. In particular, PET studies are able to measure changes in blood flow only over relatively

Voluntary self-initiated movement

Early premovement activity represented in the readiness potential, as described above, precedes self-paced voluntary movements made in the participant’s own time, not in response to any external cue. This condition of self-paced non-cued movement is problematic to study using traditional blocked-design fMRI or PET methods because of the need to control movement rate, or the “amount” of movement performed within continuous task blocks. For example, if participants perform more movements within a

Imagined movement

Imagining movement is thought to involve higher-order processes of movement preparation and planning similar to those prior to actual performed actions (Decety, 1996, Jeannerod, 1994). Functional brain imaging studies have consistently shown significant activation of the SMA and pre-SMA during imagined movement, similar to that observed for executed movements, but with reduced activation of primary motor and somatosensory areas (Dechent et al., 2004, Lotze et al., 1999, Porro et al., 2000,

Observation and imitation of others’ actions

There has been much interest recently in how the brain processes and represents the actions of others that we observe. In monkeys, “mirror neurons” within the ventral premotor cortex are active both when the animal performs a specific movement, and when it observes the same movement being performed by another monkey or a human (Gallese, Fadiga, Fogassi, & Rizzolatti, 1996). Functional brain imaging studies have revealed an analogous mirror system in humans involving regions of the premotor

Specific conclusions

It is clear from these studies that the pre-SMA does show increased premovement activity in readiness for action. Importantly, event-related and time-resolved fMRI methods do allow the investigation of such premovement activity. Although the temporal resolution of time-resolved fMRI methods is still limited by the slow and delayed hemodynamic response, temporal resolution is sufficient to provide valuable insight into processes which contribute to the preparation and readiness for action.

Our

Future directions

Forty years after the first observation of the Bereitschaftspotential – then understood simply as a slow negative potential shift preceding voluntary finger movement – we now understand much about the physiology of premovement activity in the pre-SMA and caudal SMA which gives rise to the readiness potential. However, the major question which is still unresolved is, simply, what is the function of this premovement readiness activity?

We tentatively suggest that the pre-SMA encodes motor

Acknowledgements

Our fMRI studies reviewed here were supported by the Austrian National bank Jubiläumsfonds (P9305, P10943). R. Cunnington is supported by a Fellowship of the National Health and Medical Research Council of Australia (217025).

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