Motor neglect: what do we mean?

Motor neglect: Implications for movement and rehabilitation following stroke

PURPOSE

The syndrome of unilateral neglect following stroke is associated with poor outcome and presents significant challenges to those providing therapy for affected individuals. In contrast to a number of reviews which have recently appeared in therapy and rehabilitation journals relating to sensory aspects of neglect, this review focuses on 'motor neglect'.

SEARCH STRATEGY

We searched the clinical and scientific literature for papers concerning motor neglect. The search included the databases Web of Science, Pubmed and Cinahl, primarily using the term 'motor neglect'. There was also a large degree of secondary searching involved.

DISCUSSION

Motor neglect refers to the under-utilization of a limb opposite a brain lesion that cannot be fully explained by primary sensory and motor deficits. The paper discusses classical descriptions of motor neglect and highlights the difficulties in disentangling motor neglect from hemiparesis. The related problem of motor extinction is introduced as a useful clinical measure of neglect-related movement difficulties and a significant clinical problem in its own right.

CONCLUSION

Motor neglect is a relatively under-recognized deficit which may have a significant impact on patient performance and recovery following stroke. We conclude with a discussion of the implications of motor neglect for rehabilitation, including the relative contributions that may be made by Constraint-induced movement therapy and Bilateral movement therapy in managing patients with neglect-related movement problems.

Hermann Zingerle's “Impaired Perception of the own Body Due to Organic Brain Disorders”

In the late 1970's Edoardo Bisiach and his coworkers provided definitive evidence that spatial unilateral neglect involves a disorder of the internal representation of extra-personal space. A few years later Bisiach and Berti (1987) revived the so far neglected contribution of an Austrian neurologist, Hermann Zingerle (1913). Ninety years ago Zingerle had described the symptom-complex of two right-brain-damaged patients, who showed left hemisomatoagnosia, unawareness of left hemiplegia, and left motor neglect. In addition to the detailed case reports, Zingerle had put forward a unitary interpretation of these deficits in terms of a disordered representation of one side of the body (dyschiria). A unitary representational account of these unilateral impairments was conspicuously absent in the contemporary neurological literature (Anton, Pick, Babinski), and attracted Bisiach's interest. An abridged translation of Zingerle's paper is provided. The clinical case reports and Zingerle's conclusions are discussed, with reference both to Bisiach's views, and to present knowledge of unilateral spatial neglect.

Anosognosia for left-sided motor and sensory deficits, motor neglect, and sensory hemiinattention: is there a relationship?

In recent years, research on unilateral spatial neglect has focused on dissociations between different aspects of the clinical syndrome, which is now considered by many students as a multi-componential disorder. Notwithstanding this leading view, there is at least one empirical argument which supports a unitary interpretation of the disorder. This is based on the observation, now replicated many times, that a variety of sensory stimulations (vestibular, optokinetic, transcutaneous mechanical vibration and nervous electrical, visual prism adaptation) involving a lateral change (left-right asymmetry) in the input pattern, affect in a very similar fashion virtually all manifestations of the syndrome, including: visuo-spatial neglect; hemianaesthesia (somatosensory hemi-inattention); extinction, hemiparesis, hemiplegia, and anosognosia for these motor disorders; somatoparaphrenia. These effects may be accounted for with reference to a spatial medium, articulated in a number of specific components, which is modulated by sensory input in a fundamentally similar fashion. Recent investigations concerning the neural bases of some of these stimulations support this view. In this chapter the case of the co-variation of the effects of vestibular stimulation on motor deficits and on anosognosia for hemiplegia is considered. The suggestion is made that one mechanism underlying anosognosia for hemiplegia is unawareness of a deficit of intention, or movement planning component, rather than, or in addition to, unawareness of a primary motor deficit. Temporary remission of anosognosia after vestibular stimulation may represent recovery from this neglect-related component, of which, as of other manifestations of the syndrome, patients are typically unaware. The recovered intention to move may allow the detection by the patient of the presence of a residual primary motor deficit, through a feedback mechanism.

Spatial frames of reference and somatosensory processing: a neuropsychological perspective

In patients with lesions in the right hemisphere, frequently involving the posterior parietal regions, left-sided somatosensory (and visual and motor) deficits not only reflect a disorder of primary sensory processes, but also have a higher-order component related to a defective spatial representation of the body. This additional factor, related to right brain damage, is clinically relevant: contralesional hemianaesthesia (and hemianopia and hemiplegia) is more frequent in right brain-damaged patients than in patients with damage to the left side of the brain. Three main lines of investigation suggest the existence of this higher-order pathological factor. (i) Right brain-damaged patients with left hemineglect may show physiological evidence of preserved processing of somatosensory stimuli, of which they are not aware. Similar results have been obtained in the visual domain. (ii) Direction-specific vestibular, visual optokinetic and somatosensory or proprioceptive stimulations may displace spatial frames of reference in right brain-damaged patients with left hemineglect, reducing or increasing the extent of the patients' ipsilesional rightward directional error, and bring about similar directional effects in normal subjects. These stimulations, which may improve or worsen a number of manifestations of the neglect syndrome (such as extrapersonal and personal hemineglect), have similar effects on the severity of left somatosensory deficits (defective detection of tactile stimuli, position sense disorders). However, visuospatial hemineglect and the somatosensory deficits improved by these stimulations are independent, albeit related, disorders. (iii) The severity of left somatosensory deficits is affected by the spatial position of body segments, with reference to the midsagittal plane of the trunk. A general implication of these observations is that spatial (non-somatotopic) levels of representation contribute to corporeal awareness. The neural basis of these spatial frames includes the posterior parietal and the premotor frontal regions. These spatial representations could provide perceptual-premotor interfaces for the organization of movements (e.g. pointing, locomotion) directed towards targets in personal and extrapersonal space. In line with this view, there is evidence that the sensory stimulations that modulate left somatosensory deficits affect left motor disorders in a similar, direction-specific, fashion.