Social touch is important for interpersonal interaction. Gentle touch and slow brushing are typically perceived as pleasant, the degree of pleasantness is linked to the activity of the C-tactile (CT) fibers, a class of unmyelinated nerves in the skin. The inability to experience pleasure in general is called anhedonia, a common phenomenon in the chronic pain condition fibromyalgia. Here, we studied the perception and cortical processing of gentle touch in a well-characterized cohort of fibromyalgia. Patients and controls participated in functional brain imaging while receiving tactile stimuli (brushing) on the forearm. They were asked to provide ratings of pleasantness of the tactile stimulus and ongoing pain. We found high distress, pain catastrophizing, and insomnia, and a low perceived state of health in fibromyalgia. Further, patients rated both slow (CT-optimal) and fast (CT-suboptimal) brushing as less pleasant than healthy participants. While there was no difference in brain activity during touch, patients showed deactivation in the right posterior insula (contralateral to the stimulated arm) during pleasantness rating and activation during pain rating. The opposite pattern was observed in healthy participants. Voxel-based morphometry analysis revealed reduced grey matter density in patients, in the bilateral hippocampus and anterior insula. Our results suggest anhedonia to gentle touch in fibromyalgia with intact early-stage sensory processing but dysfunctional evaluative processing. These findings contribute to our understanding of the mechanisms underlying anhedonia in fibromyalgia.

中文翻译：

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纤维肌痛的轻度快感缺乏症：感觉正常，但评估异常。

社会交往对于人际互动很重要。温柔的触摸和缓慢的刷牙通常被认为是令人愉悦的，愉悦的程度与C触觉（CT）纤维（皮肤中一类无髓神经）的活性有关。通常无法享受愉悦感的人被称为快感缺乏症，这是慢性疼痛性纤维肌痛的常见现象。在这里，我们研究了特征性纤维肌痛队列中轻触的感觉和皮质处理。患者和对照组在前臂接受触觉刺激（刷牙）的同时参与了功能性脑成像。他们被要求提供触觉刺激和持续疼痛的等级。我们发现，纤维肌痛患者的痛苦高，灾难性，失眠多，健康状况低。进一步，与健康参与者相比，慢刷（CT最佳）和快刷（CT次最佳）的患者均较不满意。虽然在触摸过程中脑部活动没有差异，但是患者在愉悦感等级中显示出右后岛的被激活（与受刺激的手臂相对），而在疼痛等级中表现出了激活。在健康参与者中观察到相反的模式。基于体素的形态计量学分析显示，双侧海马和前岛中患者的灰质密度降低。我们的结果表明，缺乏完整的早期感觉过程，但评估功能障碍的纤维肌痛患者轻度触摸。这些发现有助于我们了解纤维肌痛中无力症的潜在机制。