Paul D. McGeoch

Apotemnophilia: a neurological disorder

Apotemnophilia, a disorder that blurs the distinction between neurology and psychiatry, is characterized by the intense and longstanding desire for amputation of a specific limb. Here we present evidence from two individuals suggestive that this condition, long thought to be entirely psychological in origin, actually has a neurological basis. We found heightened skin conductance response to pinprick below the desired line of amputation. We propose apotemnophilia arises from congenital dysfunction of the right superior parietal lobule and its connection with the insula.

Size reduction using Mirror Visual Feedback (MVF) reduces phantom pain

Following limb amputation patients continue to feel the vivid presence of a phantom limb. A majority of patients also experience pain in the phantom and sometimes (as in our case DS) the pain is severe. Remarkably we find that optically ‘resurrecting’ the phantom with a mirror and using a lens to make the phantom appear to shrink caused the pain to ‘shrink’ as well.

Rapid Relief of Thalamic Pain Syndrome Induced by Vestibular Caloric Stimulation

Central post-stroke pain syndrome develops in a minority of patients following a stroke. The most usual causative lesion involves the lateral thalamus. The classic presentation is of severe, unrelenting pain that involves the entire contralateral half of the body. It is largely refractory to current treatments. We found that in two patients with this condition their pain was substantially improved by vestibular caloric stimulation, whereas placebo procedures had no effect. We proposed that this is because vestibular stimulation activates the posterior insula, which in turn inhibits the generation of pain in the anterior cingulate.

Behavioural evidence for vestibular stimulation as a treatment for central post-stroke pain

Background: Central post-stroke pain (CPSP) is often resistant to treatment. We have previously proposed that caloric vestibular stimulation might alleviate it. Methods: We conducted a single blind placebo controlled investigational study of caloric vestibular stimulation (CVS) in nine patients with CPSP. Participants rated their pain levels before and after the procedure on a 10 point scale. Results: We found a significant immediate treatment effect of the cold water caloric stimulation with an average pain reduction of 2.58 points (SEM 0.52) for the experimental condition compared with 0.54 points (SEM 0.49) for the placebo conditions. Conclusions: Participants who responded best to CVS had suffered strokes that spared and permitted activation of the dominant parieto-insular vestibular cortex (PIVC), which is known to be located in the non-dominant hemisphere. These findings tie in closely with the thermosensory disinhibition hypothesis for central pain, which leads us to propose that vestibular stimulation may alleviate CPSP from cross activation between the PIVC and the thermosensory cortex in the adjacent dorsal posterior insula. Alternatively, if one views vestibular function and thermoregulation as part of a larger interoceptive system that exists to maintain homeostasis, then it is possible they share a common integrative mechanism in the brainstem, which may act to reset the balance in central pain.

Dynamic reorganization of referred sensations by movements of phantom limbs

After amputation of an arm the sensory map of the body changes radically, causing the sensory input from face to ‘invade’ the original hand area in the brain. As a result, touching the face of the amputee evokes tactile sensations on the phantom. These sensory referrals from the face to phantom hand occur in a stable, topographically organized manner. We now find that volitional movements of the phantom cause striking, systematic shifts in the map along the direction of movement. We conclude that the reorganization of maps is based partly on reversible inhibition of ordinarily silent synapses, not entirely on new anatomical connections. This finding further highlights the dynamic nature of the brain on remarkably short-time scales.

Post-stroke tactile allodynia and its modulation by vestibular stimulation: a MEG case study.

Background –  There 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.

Sexual and Food Preference in Apotemnophilia and Anorexia: Interactions between ‘Beliefs' and ‘Needs' Regulated by Two-Way Connections between Body Image and Limbic Structures

Apotemnophilia straddles the boundary between neurology and psychiatry. It is a condition in which individuals experience the strong and specific desire for amputation of a healthy limb. Research suggests this disorder may be of neurological origin, specifically that the body image centers of the brain lack a cortical representation for a particular limb. A curious aspect of this condition is that sufferers often report an attraction to amputees in addition to desiring their own limb be removed. We postulate that sexual ‘aesthetic preference’ for certain body morphology is dictated in all individuals in part by the cortical representation of ones body image.

The appearance of new phantom fingers post-amputation in a phocomelus

We report the unusual case of a woman with right upper limb phocomelia who, post-amputation of her right hand following trauma, sprouted a phantom hand that contained five digits, including a phantom thumb and index finger that had been absent since her birth. These two phantom digits were initially half normal size, however, more than three decades later, with mirror visual feedback treatment, she was able to elongate them to normal length. This suggests that a hardwired representation of a complete hand had always been present in her brain, but inhibited by the presence of afferents from the phocomelic hand. Amputation of the phocomelic hand then led to disinhibition of this dormant representation, and the emergence of a phantom hand with five fingers, which was then further enhanced by false visual feedback from a mirror. The case powerfully demonstrates the interaction of nature and nurture in creating and sustaining body image.

Primary somatosensory cortex hand representation dynamically modulated by motor output

The brain’s primary motor and primary somatosensory cortices are generally viewed as functionally distinct entities. Here we show by means of magnetoencephalography with a phantom-limb patient, that movement of the phantom hand leads to a change in the response of the primary somatosensory cortex to tactile stimulation. This change correlates with the described conscious perception and suggests a greater degree of functional unification between the primary motor and somatosensory cortices than is currently realized. We suggest that this may reflect the evolution of this part of the human brain, which is thought to have occurred from an undifferentiated sensorimotor cortex.

Modulation of Body Mass Composition using Vestibular Nerve Stimulation.

There is increasing evidence of a “set-point” for body weight in the brain, that is regulated by the hypothalamus. This system modifies feeding behavior and metabolic rate, to keep body fat within predetermined parameters. It is also known that animals subjected to chronic centrifugation show a reduction in body fat. Experiments with mutant mice found that this loss of fat appears to be mediated by a vestibulo-hypothalamic pathway. Vestibular nerve stimulation (VeNS), also known as galvanic vestibular stimulation, involves non-invasively stimulating the vestibular system by applying a small electrical current between two electrodes placed over the mastoid processes. We suggest that any means of repeatedly stimulating the otolith organs in humans would cause a reduction in total body fat, and that VeNS would be a useful technique to use in this regard. Below we provide pilot data to support this idea.