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Universiteit Leiden

It’s all in the eyes: How transcutaneous vagus nerve stimulation (tVNS) promotes sociability

It’s all in the eyes: How transcutaneous vagus nerve stimulation (tVNS) promotes sociability

“Where words are restrained, the eyes often talk a great deal” - Samuel Richardson. We often hear phrases like these, but do the eyes really “say it all?”

Imagine you’re having a conversation with a friend and all of a sudden, they look away and are no longer paying attention to you. Do you turn your gaze to their direction? Do you wait until you have their attention back again? Or do you walk out in frustration, consumed by thoughts of not being interesting enough? I bet we all felt a tinge of discomfort in these disrupted social situations. But why should this one action coming from someone else consume us with all these cognitively demanding thoughts, preventing us from deciding our next course of action swiftly?

 

Your survival instincts

From an evolutionary standpoint, we are equipped with the ability to quickly decide what actions to take in a given situation without spending too much time. We are able to do this so efficiently because we are good at picking up the most noticeable sensory features from our social environment. Any unnoticeable features mean longer processing times that could potentially harm efficient decision-making in subsequent events.

 

Hints from human emotions and the eyes

Equipped with a social brain, not only can we recognize emotions in others, we want others to recognize our empathetic side as well. This non-verbal facial expression provides a sense of communal understanding between people, allowing for efficient social communication with minimum difficulty. The vagus nerve (tenth cranial nerve) has been shown to be involved in social engagement by allowing us to easily recognize emotions in faces rather than bodies. It does this by allowing us to pick up the most salient cues that are displayed in our basic human emotions. A study showed that by stimulating the vagus nerve, people were able to infer emotions from the eye region. But, they were only able to do this with easy items (salient social cues; relating to basic emotions) and not with difficult ones (subtle social cues; relating to intentions and beliefs). That being said, the eyes locked within an emotion provides an important social cue that helps us recognize the intentions of the viewer, depending on where they are focusing their gaze.

 

Allocation of attention to relevant stimuli

A direct gaze reduces the processing of irrelevant information during social engagement. This means that we wouldn’t need to use up our already limited working-memory capacity, and instead, we could save it for the recognition of other, more subtle events that we would have otherwise missed.

 

Recently, we performed a new study to demonstrate whether transcutaneous vagus nerve stimulation (tVNS) can enhance people’s ability to recognize gaze direction fast enough to overcome the attentional blink effect. To do this, we used the Rapid Serial Visual Presentation where healthy participants had to determine two things: (1) the gender of an image with three different emotional expressions (e.g. anger, fear, neutral) with either an averted or direct gaze, and (2) the orientation (e.g. clockwise vs. counterclockwise) of a rotated landscape. We found that stimulating the vagus nerve enhanced people’s ability to recognize direct gaze (rather than averted gaze), which further improved their accuracy in reporting the orientation of a landscape. This suggested that active tVNS acted as a means to improve performance in an attentional blink task by reducing the allocation of attention to irrelevant information (i.e. emotions and gender). A direct gaze suggests that we are the focus of the observer’s attention, so no further disruptions are present in the way of successfully reporting subsequent target stimuli.

 

So, how can tVNS improve sociability?

It’s clear that the vagus nerve is involved in regulating social engagement via recognition of salient social cues. Going back to the first question as to why a sudden averted gaze might become so cognitively demanding is probably because you lost track of all the salient social cues that once used to inform you that you were the focus of attention. The evidence so far teaches us that tVNS is a potential tool that can help us recognize the most immediate things fast enough to be able to maintain smooth social engagements. Our findings also promote tVNS as a potential tool for people with autism. It can help with sociability by reducing social ambiguity posed by eye contact. People with ASD could be able to perceive the eyes merely in its saliency to promote attentional resources for social communication instead. So, the eyes may not necessarily "say it all", but they sure do spare you a lot of attention to make a social situation less awkward and swift if you maintain that eye contact. And perhaps, armed with empirical findings, it would make more sense to change the saying to, "tVNS helps the eyes say it all".

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