Motor role of human inferior parietal lobe revealed in unilateral neglect patients


The exact role of the parietal lobe in spatial cognition is controversial. One influential hypothesis proposes that it subserves spatial perception1, whereas other accounts suggest that its primary role is to direct spatial movement2,3. For humans, it has been suggested that these functions may be divided between inferior and superior parietal lobes, respectively2,4. In apparent support of a purely perceptual function for the inferior parietal lobe (IPL), patients with lesions to this structure, particularly in the right hemisphere, exhibit unilateral spatial neglect (deficient awareness for the side of space opposite to that of their lesion)5. Here we show that patients with right IPL lesions also have a specific difficulty in initiating leftward movements towards visual targets on the left side of space. This motor impairment was not found in neglect patients with frontal lesions, contrary to previous proposals that motor aspects of neglect are particularly associated with anterior damage6,7,8,9. Our results suggest that the human IPL operates as a sensorimotor interface, rather than subserving only perceptual functions.

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Figure 1: Reaction times to left or right visual targets were measured in a reaching task (experiment 1) and a no-reach task (experiment 2) using the same apparatus.
Figure 2: Extent of right-hemisphere lesions in neglect patients.
Figure 3: Mean reaction time (RT) to initiate movements towards left versus right targets, from three different start positions in the reaching task of experiment 1.
Figure 4: Mean RT to detect left versus right targets, for the three different hand positions in the no-reach task of experiment 2.


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We thank J. Wade and A. Rudd, and the staff and patients of the stroke units at Charing Cross Hospital and St. Thomas' Hospital, London. This research was supported by the Stroke Association and the Wellcome Trust. J.B.M. was supported by a National Health and Medical Research Council (Australia) Neil Hamilton Fairley Fellowship, and by AMRAD Australia.

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Correspondence to Masud Husain.

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Mattingley, J., Husain, M., Rorden, C. et al. Motor role of human inferior parietal lobe revealed in unilateral neglect patients. Nature 392, 179–182 (1998).

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