The hidden side of body integrity dysphoria: aberrant limbic responses to dynamic touch

Body integrity dysphoria (BID) is a brain-based disorder characterized by a persistent, obsessing and disturbing desire for the amputation of healthy limbs. Importantly, individuals with BID are adamant about which specific body segment they wish to have amputated and the exact level at which the amputation should occur. The condition has been linked to altered resting-state brain functional connectivity and task-based activity at the level of somatosensory cortices. However, the inevitable distress associated with the condition has not been explained by current neurophysiological data. In this functional MRI (fMRI) study, we studied individuals with a lifelong desire for the amputation of their left leg using a dynamic somatosensory stimulation paradigm. We identified and marked the desired line of amputation on the BID individuals' left leg and a corresponding point on their right leg. We measured brain activations in response to stimulation of the lower limbs while participants were instructed to focus on the tactile sensations and detect when the stimulation crossed the line of the desired amputation. Compared with healthy controls focusing on the same segments of their legs, individuals with BID showed higher neural activations specifically for the stimulation of their left leg in a large cortical and subcortical neural network primarily associated with rewarding and pain stimuli. Some of these hyperactivations were particularly marked immediately after the stimulation had passed over the line of the desired amputation. When the stimulation crossed the desired point of amputation, there were also increased activations in the premotor cortices and the anterior cingulum, a sign of premotor attentional arousal. Our data show a pathological relationship between altered neural representations of the body map and the brain reward system, connecting BID to the visceral brain for the first time.