In an eyebrow-raising new paper, neuroscientists report that they had participants wear a ball gag while watching images of people in pain. The lucky participants in this neuro-bondage were all female BDSM submissives, and their brain activity in response to the painful pictures was recorded with EEG.

Here’s the article: Embodiment and Humiliation Moderation of Neural Responses to Others’ Suffering in Female Submissive BDSM Practitioners

And here’s some of the stimuli (I assume they were not blurred-out in the real study):

According to authors Siyang Luo and Xiao Zhang, the rationale for the experiment was that the ball gag might inhibit the brain’s empathetic response to suffering by preventing facial muscle movements. This would be in line with embodied emotion theories, which posit that our facial expressions can actually drive our emotional reactions.

Indeed, the data showed that compared to a control condition (no ball gag), gagging seemingly inhibited neural responses to the pain-filled images:

Our results showed that during the use of a ball gag to prevent facial muscle movement and facial mimicry, the neural responses to others’ suffering at N1, early LPP, and late LPP were inhibited compared to the responses under the relaxed condition. (N1, early LPP and late LPP are different stages of the neural response to visual stimuli.)

However, some of these differences were marginal, and ironically the brain responses to ‘sadistic painful’ stimuli (yellow bars) were least affected by the gag, while neutral stimulus responses were most altered, which is hard to explain:

Another concern with a study using this design is that the gag may have triggered electrical activity in the jaw and face muscles that could contaminate the EEG signal, although the authors did take account of this and used filtering to mitigate the problem.

Luo and Zhang conclude that

Physical restriction during BDSM practices (wearing a ball gag) affects individuals’ neural responses to others’ suffering in both sexual sadistic contexts and general contexts… future research should aim to further clarify whether and how various activities (e.g., bondage and roleplaying) during BDSM practices shape the perceptions of others’ feelings.

The ball gag design is essentially a sexed-up version of the famous “pen-in-the-mouth” psychology experiments which helped to launch the theory of embodied emotion (although these classic experiments recently failed to replicate.) In fact, an EEG study similar to this one, but with a pen instead of a ball gag, was recently published.