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Non-spatially lateralized mechanisms in hemispatial neglect

Nature Reviews Neurosciencevolume 4pages2636 (2003) | Download Citation

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Abstract

Hemispatial neglect is a common, disabling disorder that results from brain damage, most frequently stroke. Research on patients with neglect has provided important insights into normal brain mechanisms involved in directing attention, representing space and controlling movement. Although much work has focused on the lateralized components of neglect, recent investigations have also revealed deficits that are not spatially lateralized, consistent with new findings from functional imaging, human neuropsychological and monkey electrophysiological studies. Here we propose that understanding the interactions between spatially lateralized and non-lateralized mechanisms provides important insights into the neglect syndrome and the normal functions of brain structures that are commonly damaged in neglect patients, and will contribute to the development of treatments for the condition.

Key Points

  • Neglect patients suffer pronounced spatially lateralized impairments, involving difficulties in perceiving and responding to items on the side of space opposite to the side of brain damage. So far, most research has focused on these lateralized deficits. Here we propose that neglect patients typically also have deficits that are not necessarily worse towards one side of space and that such impairments exacerbate their difficulties. Understanding these non-spatially lateralized mechanisms might help to clarify the variability found among patients, lead to improved therapy and improve our understanding of the intact human brain.

  • We review the spatially lateralized deficits that are typically seen in patients suffering from neglect. We argue that a lateralized deficit is necessary, but perhaps not sufficient, to describe the behavioural deficits seen in neglect.

  • Neglect patients show perceptual deficits on tasks that do not require spatially lateralized orienting or selection. Recent studies have highlighted problems with non-spatially lateralized selective attention, sustained attention, and trans-saccadic working memory. Although not all neglect patients show all such deficits, each deficit alone could aggravate the lateralized deficits seen in neglect.

  • Functional imaging data also show that non-lateralized tasks often involve the regions of the brain that are damaged in neglect patients. Furthermore, different tasks appear to activate neighbouring but anatomically distinct regions, suggesting that a number of different functional modules might often be involved in neglect.

  • We propose that non-spatially lateralized and lateralized deficits might combine to produce the impairments seen in individual patients. Future studies should examine both types of deficit. On the basis of neuroimaging research, we predict that the patterns of impairment will correspond with the extent and location of the lesions.

  • Acknowledging and understanding the non-spatially lateralized functions of the brain regions involved in neglect leads to clear implications for rehabilitation. Once these mechanisms are understood, a patient's individual pattern of deficit might be dealt with more effectively, using pharmacological and/or behavioural interventions.

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Acknowledgements

This research is funded by a grant to M.H. from the Wellcome Trust. We thank J. Driver, C. Kennard, P. Malhotra, S. Mannan, D. Mort & A. Parton for their help.

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Affiliations

  1. Division of Neuroscience and Psychological Medicine, Imperial College, Charing Cross Hospital, London, W6 8RF, UK

    • Masud Husain
  2. Institute of Cognitive Neuroscience, University College London, London, WC1N 3AR, UK

    • Masud Husain
  3. School of Psychology, University of Nottingham, Nottingham, NG7 2RD, UK

    • Chris Rorden

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FURTHER INFORMATION

Encyclopedia of Life Sciences

stroke

MIT Encyclopedia of Cognitive Sciences

attention

eye movements and visual attention

visual neglect

Glossary

STROKE

Brain damage that is caused by a lack of blood supply, as a result of either blockage or rupture of a cerebral blood vessel.

CANCELLATION TASK

A bedside clinical task in which patients have to find and mark targets that are usually displayed on a sheet of paper either on their own or with distracting non-targets.

SACCADE

A rapid eye movement that brings the fovea (the central retinal area with the highest resolution) to view a point of interest in a visual scene.

BALINT'S SYNDROME

A rare disorder following bilateral parieto-occipital lesions in which the patient has difficulties in directing the eyes to visual objects (ocular apraxia), misreaching to peripheral visual targets (optic ataxia) and perceives only one object at a time (simultanagnosia).

SIMULTANAGONOSIA

Sometimes also referred to as 'simultagnosia', this is the inability to perceive more than one object at one time.

SPATIAL WORKING MEMORY

The ability to hold 'on-line' and manipulate information regarding the location of an object.

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