• P D McGeoch, L E Williams, T Song, R R Lee, M Huang, and V S Ramachandran.
• Center for Brain and Cognition, University of California, San Diego, CA 92093-0109, USA. pmcgeoch@mac.com
• Acta Neurol. Scand. 2009 Jun 1; 119 (6): 404-9.

BackgroundThere is behavioural evidence that caloric vestibular stimulation (CVS) can alleviate central pain. Several such patients have also noted that it reduces tactile allodynia, an especially ill-understood phenomenon in these patients.Aims Of The StudyThe first aim is to use magnetoencephalography (MEG) to study neural activity associated with tactile allodynia in central post-stroke pain (CPSP). The second is to assess how this would be affected, if at all, by CVS. The third is to assess the ability of the VESTAL solution for MEG to detect anterior cingulate activation.MethodsA 58-year-old woman with CPSP, and marked unilateral tactile allodynia, participated in a MEG study with imaging pre- and post-CVS.ResultsTactile simulation within the patient's allodynic area resulted in contralateral activation of the primary motor and anterior cingulate cortices, which had normalized 24 h post-CVS.ConclusionsWe suggest that the unexpected primary motor cortex activation in response to light touch in the allodynic area arises from inappropriate activation of a normal mechanism, which may occur when a threat to homeostasis is present, to lower motor thresholds and allow for more rapid performance of corrective actions. We propose this may be mediated by the interoceptive cortex in the dorsal posterior insula.

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