Elsevier

NeuroImage

Volume 20, Supplement 1, November 2003, Pages S89-S100
NeuroImage

Regular article
The left parietal and premotor cortices: motor attention and selection

https://doi.org/10.1016/j.neuroimage.2003.09.011Get rights and content

Abstract

It is well established that the premotor cortex has a central role in the selection of movements. The role of parts of the parietal cortex in movement control has proved more difficult to describe but appears to be related to the preparation and the redirection of movements and movement intentions. We have referred to some of these processes as motor attention. It has been known since the time of William James that covert motor attention can be directed to an upcoming movement just as visuospatial attention can be directed to a location in space. While some parietal regions, particularly in the right hemisphere, are concerned with covert orienting and the redirecting of covert orienting it may be useful to consider other parietal regions, in the anterior inferior parietal lobule and in the posterior superior parietal lobule, particularly in the left hemisphere, as contributing to motor attention. Such parts of the parietal lobe are activated in neuroimaging experiments when subjects covertly prepare movements or switch intended movements. Lesions or transcranial magnetic stimulation (TMS) affect the redirecting of motor attention. The difficulties apraxic patients experience when sequencing movements may partly be due to an inability to redirect motor attention from one movement to another. The role of the premotor cortex in selecting movements is also lateralized to the left hemisphere. Damage to left hemisphere movement selection mechanisms may also contribute to apraxia. If, however, it remains intact after a stroke then the premotor cortex may contribute to the recovery of arm movements. A group of patients with unilateral left hemisphere lesions and impaired movements in the contralateral right hand was studied. Functional magnetic resonance imaging showed that in some cases the premotor cortex in the intact hemisphere was more active when the stroke-affected hand was used. TMS in the same area in the same patients had the most disruptive effect on movements. In summary, patterns of motor impairment and recovery seen after strokes can partly be explained with reference to the roles of the parietal and premotor cortices in motor attention and selection.

Introduction

The premotor cortex has a central role in selecting movements while the parietal cortex is concerned with the preparation and redirection of movements and movement intentions Kalaska and Crammond, 1995, Rushworth et al., 2001a, Thoenissen et al., 2002. The same brain areas and cognitive processes must be discussed in any account of apraxia or motor recovery after stroke; apraxic patients' lesions cluster around the intraparietal sulcus and parts of the frontal lobe (Haaland et al., 2000) and new patterns of activation appear in such regions as patients recover movement skills after brain damage Johansen-Berg, 2002a, Johansen-Berg and Matthews, 2002.

Section snippets

The organization of attention systems within the parietal cortex

The involvement of the parietal cortex in coding space and in directing spatial attention is well established Bremmer et al., 2001a, Halligan et al., 2003. The firing rates of parietal neurons change in tandem with the direction of attention (Colby and Goldberg, 1999) and neuroimaging studies have identified signal modulations in the human parietal cortex in similar situations Corbetta and Shulman, 2002, Nobre, 2001. The ability to represent extrapersonal space and to direct attention within

Covert preparatory motor attention

Paradigms in which subjects covertly prepare for stimuli appearing in a certain part of the visual field are well established as ways of investigating oculomotor attention (Pashler, 1998). Reaction times (RTs) are quicker when subjects are able to prepare for a stimulus' appearance at a particular position. Although it may be possible to covertly orient attention in such paradigms without making an overt eye movement it is clear from both behavioral and neuroimaging experiments that the two

The left parietal cortex and covert motor attention

Before considering the evidence that links the left parietal cortex with motor attention it is worth recalling the evidence that relates covert orienting attention to other parietal areas. Two types of experiments have implicated the posterior parietal cortex, particularly in the right hemisphere, with the covert orienting of attention. First, neuroimaging experiments have shown that when subjects are covertly orienting to stimuli there is an increase in activation in the posterior parietal

Motor attention after left parietal lesions

Not only does TMS disrupt the redirection of motor attention, but lesions that include the same area have a similar effect Castiello and Paine, 2002, Rushworth et al., 1997c. Rushworth and colleagues compared performance on a motor attention redirection task in three groups of subjects: nine patients with lesions that included the left parietal cortex, nine patients with lesions that included the right parietal cortex, and a set of age-matched healthy controls. Patients performed the task with

Tool use and left parietal lesions

The updating of motor attention, if it is defined as the updating of the representation of the body and limbs, can also be invoked to help explain the role of the parietal cortex in tool use; when a person uses a tool the representation of the body plan must be updated to accommodate the tool. For example, a person using a hammer has a longer reach by virtue of the hammer's length. A failure to update the body representation appropriately would mean that the person attempting to hit a nail

The left premotor cortex and movement selection

While the parietal cortex may have a complex role in the preparation and redirection of movements and movement intentions, both single neuron recording and human neuroimaging studies indicate that the premotor cortex has a well-defined role in the selection of movements for execution Kalaska and Crammond, 1995, Thoenissen et al., 2002. Once again neuroimaging and TMS experiments indicate that the premotor cortex in the left hemisphere has the dominant role.

Different parts of the premotor cortex

The premotor cortex, motor impairment, and motor recovery after stroke

Disruption of such movement selection mechanisms may have some relevance for understanding the impairments of patients with lesions in the left hemisphere. Left hemisphere lesions have a particularly disruptive effect on the ability of patients to select between movements according to arbitrary rules (Rushworth et al., 1998). An impairment of such a mechanism may contribute to the difficulties that some apraxic patients with left hemisphere lesions have in selecting the appropriate movements in

Conclusions

While the premotor cortex is concerned with the selection of a movement for execution, parietal neurons are modulated when movements are prepared or redirected Kalaska and Crammond, 1995, Rushworth et al., 2001a, Thoenissen et al., 2002, a function that we have summarized with the term “motor attention.” In the cases of both the parietal and the premotor cortices of the human brain, the dominant role in motor attention and selection is played by areas in the left hemisphere. Some of the

Acknowledgements

This work was supported by core funding from the Medical Research Council, Medical Research Council grants (M.F.S.R., J.T.D.), the Wellcome Trust (H.J.-B.), Jesus College (S.M.G.), and the Royal Society (M.F.S.R.).

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