Impaired Imagery for Upper Limbs
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The brain processes associated with mental imagery have long been a matter of debate. Neuroimaging and neuropsychological studies have yielded diverging evidence of mental transformation activating the right hemisphere, the left hemisphere, or both. Here, using a mirror/normal discrimination task with rotated body parts (BPs) and external objects (EOs), we describe the case of a patient who developed a selective deficit in mental imagery of such BPs due to left posterior parietal brain damage. In addition, the patient’s deficit predominated for pictures of right arms (i.e., arms corresponding to the patient’s imagined contralesional arm) and was further characterised by an inability to distinguish between anatomically possible and impossible arm positions. This neuropsychological deficit was corroborated by neuroimaging evidence revealing the absence of activation in the left parietal lobe for the mental rotation of body parts as shown in healthy participants. In contrast, his behavioural performance and brain activation for EOs were similar to those of healthy participants. These data suggest that mental imagery of BPs and EOs relies on different cognitive and neural mechanisms and indicate that the left posterior parietal lobe is a necessary structure for mental transformations of human BPs.
KeywordsBody parts Electric source imaging ERP mapping Mental rotation
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This research was supported by an iMURS Scholarship from Macquarie University to L. Overney. We thank Irina Harris for her constructive comments on a previous version of the manuscript and Christoph Michel for allowing us to use the infrastructure of the Functional Brain Mapping Laboratory (Geneva, Switzerland). We thank Denis Brunet for providing Cartool and Martine Lamon for her help in collecting part of the data.
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