The acquisition and extinction of fear of painful touch: a novel tactile fear conditioning paradigm

Fear of touch, due to allodynia and spontaneous pain, is not well-understood. Experimental methods to advance this topic are lacking, and therefore we propose a novel tactile conditioning paradigm. Seventy- six pain-free participants underwent acquisition in both a predictable and unpredictable pain context. In the predictable context, vibrotactile stimulation was paired with painful electrocutaneous stimulation (simulating allodynia). In the unpredictable context, vibrotactile stimulation was unpaired with pain (simulating spontaneous pain). During an extinction phase, a cue exposure and context exposure group continued in the predictable and unpredictable context, respectively, without pain. A control group received continued acquisition in both contexts. Self- reported fear and skin conductance responses (SCRs), but not startle responses, showed fear of touch was acquired in the predictable context. Context-related startle responses showed contextual fear emerged in the unpredictable context, together with elevated self-reported fear and SCRs evoked by the unpaired vibrotactile stimulations. Cue exposure reduced fear of touch, whilst context exposure reduced contextual fear. Thus, painful touch leads to increased fear, as does touch in the same context as unpredictable pain, and extinction protocols can reduce this fear. We conclude that tactile conditioning is valuable for investigating fear of touch and can advance our understanding of chronic pain.status: publishe