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.

Keywords: body integrity dysphoria; body ownership; fMRI; tactile stimulation; xenomelia.

© The Author(s) 2025. Published by Oxford University Press on behalf of the Guarantors of Brain.

身体完整性异觉症（BID）是一种以持久、困扰且强烈的健康肢体截肢欲望为特征的脑部疾病。重要的是，患有 BID 的个体坚决指出他们希望被截除的具体身体部位以及确切的截肢位置。该病症与静息状态下的大脑功能连接和感觉皮层任务相关活动的变化有关。然而，当前的神经生理学数据无法解释这种不可避免的痛苦。在本项功能性磁共振成像（fMRI）研究中，我们使用动态的感觉刺激模式来研究那些一生都想截除左腿的人群。我们在 BID 个体的左腿上标出了他们想要的截肢线，并在其右腿对应的位置做了标记。在实验过程中，参与者被要求关注腿部触觉并检测刺激何时经过预定的截肢线，在此期间我们测量了大脑激活情况。与健康对照组专注于其腿部相同部位时相比，BID 患者在左侧腿部受刺激时表现出更大的神经激活，在主要与奖励和疼痛刺激相关的皮层和亚皮层神经系统中尤为显著。其中一些过度激活尤其出现在刺激经过预定截肢线之后。当刺激通过预定的截肢点时，前运动皮质和扣带回区域还出现了更强的激活，这是前运动注意唤醒的标志。我们的数据表明身体地图神经表征与大脑奖赏系统之间的病理关系，并首次将 BID 与内脏脑联系起来。

关键词：身体完整性异觉症；身体所有权；fMRI；触觉刺激；异肢症。

© The Author(s) 2025. Published by Oxford University Press on behalf of the Guarantors of Brain.