Xenomelia: a new right parietal lobe syndrome
- 1Center for Brain and Cognition, University of California, San Diego, La Jolla, California, USA
- 2Department of Radiology, University of California, San Diego, La Jolla, California, USA
- Correspondence to Dr Paul D McGeoch, Center for Brain and Cognition, University of California, San Diego, La Jolla, CA 92093, USA;
Contributors PDM: Developed theories, recruited subjects, established links with MEG Center, designed the study, examined and carried out experimental protocols and wrote the paper. DB: Handled the operation of MEG machine and data processing and wrote the paper, especially the more technical aspects and development of theories. TS: Gathered MEG data and trained DB on the finer points of MEG analysis. RRL: Interpreted MRI/MEG images. MH: Provided expert analysis of MEG data. VSR: Developed the theories, wrote the paper and examined the subjects.
- Received 16 April 2011
- Accepted 22 May 2011
- Published Online First 21 June 2011
Background Damage to the right parietal lobe has long been associated with various disorders of body image. The authors have recently suggested that an unusual behavioural condition in which otherwise rational individuals desire the amputation of a healthy limb might also arise from right parietal dysfunction.
Methods Four subjects who desired the amputation of healthy legs (two right, one left and one, at first, bilateral and then left only) were recruited and underwent magnetoencephalography (MEG) scans during tactile stimulation of sites above and below the desired amputation line. Regions of interest (ROIs) in each hemisphere (superior parietal lobule (SPL), inferior parietal lobule, S1, M1, insula, premotor cortex and precuneus) were defined using FreeSurfer software.
Results Analysis of average MEG activity across the 40–140 ms post-stimulation timeframe was carried out using an unpaired t test. This revealed significantly reduced activation only in the right SPL ROI for the subjects' affected legs when compared with both subjects' unaffected legs and that of controls.
Conclusions The right SPL is a cortical area that appears ideally placed to unify disparate sensory inputs to create a coherent sense of having a body. The authors propose that inadequate activation of the right SPL leads to the unnatural situation in which the sufferers can feel the limb in question being touched without it actually incorporating into their body image, with a resulting desire for amputation. The authors introduce the term ‘xenomelia’ as a more appropriate name than apotemnophilia or body integrity identity disorder, for what appears to be an unrecognised right parietal lobe syndrome.
- behavioural neurology
- body image
- body integrity identity disorder
- parietal lobes
PDM and DB are joint status authors.
Funding This work is partly funded by the Herb Lurie Foundation, which had no direct input into this study.
Competing interests None.
Ethics approval Ethics approval was provided by UCSD Institutional Review Board.
Provenance and peer review Not commissioned; externally peer reviewed.