Real-time eye contact between two people generates shared and prepares both brains for social interaction via cerebellum-to-cerebrum networks that include the limbic mirror system, according to a new study (Koike et al., 2019) published today in the journal eNeuro.

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Norihiro Sadato of the National Institute for Physiological Sciences in Japan was the senior author of this paper, "What Makes Eye Contact Special? Neural Substrates of On-Line Mutual Eyegaze: A Hyperscanning fMRI Study." (The term "mutual eyegaze" is synonymous with "holding eye contact" with another person.)

This state-of-the-art neuroimaging research on mutual gaze helps us better understand how substrates throughout the whole-brain (including specific regions within cerebral and cerebellar hemispheres) work together to make real-time eye contact a core tenant of shared mental states during effective social interactions.

Notably, when two individuals were making real-time eye contact during this lab experiment, their eye-blink patterns synchronized via automatic mimicry and the same regions of each person’s brain “lit up” simultaneously inside two "hyperscanning" fMRI brain scanners that were linked by a live video camera feed.

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As the authors explain, “Eye contact is a key element that connects humans during social communication. We focused on a previously unaddressed characteristic of eye contact: real-time mutual interaction as a form of automatic mimicry. Our results indicate that real-time interaction during eye contact is mediated by the cerebellum and limbic mirror system. These findings underscore the importance of the mirror system and cerebellum in real-time social interaction.”

The cohort used for this study consisted of sixteen pairs of healthy human adults without a history of neurological or illness. The 34 participants recruited for this study were all volunteers who hadn't met before the experiment.

This three-phase study included a LIVE assessment of brain activity during real-time eye contact using a double-video system, an off-line REPLAY phase which delayed the video feed by 20 seconds (without participants' knowledge), and a REST (baseline) phase when volunteers were asked to gaze at a blank screen.

During the LIVE and REPLAY phase of the experiment, each participant was given cues to gaze into his or her video partner’s right or left eye and to contemplate what he/she might be thinking, his/her traits, and how he/she was feeling in that moment.

Source: Koike et al., eNeuro (2019)

Interestingly, as you can see in the brain images and diagrams above, Koike et al. found that during the LIVE condition there was greater activation in the left cerebellar hemisphere, vermis, and anterior cingulate cortex ACC. This was accompanied by enhanced functional connectivity between ACC and the right anterior insula (AIC).

The researchers speculate about why these brain activation and connectivity changes occurred during LIVE eye contact between study participants: “Given the roles of the cerebellum in sensorimotor prediction and ACC in movement initiation, ACC–cerebellar activation may represent their involvement in modulating visual input related to the partner’s movement, which may, in turn, involve the limbic mirror system. Our findings indicate that mutual interaction during eye contact is mediated by the cerebellum and limbic mirror system."

In their paper, Sadato and his co-authors share several noteworthy limitations of this study:

"First, concerning the hyperscanning-fMRI experimental design, the very long mutual gaze condition was not ecological and may be quite different from conceptions of ‘mutual gaze’ or ‘eye-contact’ informed by daily life. This is due to our use of a blocked-design, the most effective way to detect brain activation. Also, the product of our experimental design, estimations of the temporal dynamics of eye-blink , brain activation, and inter-brain synchronization could not be performed. While we could not find a significant effect of session on the eye-blink entrainment in real-time eye-contact, it is possible that the eye-blinking entrainments only occur in the very first phase of mutual gaze condition in one block. By refining the experimental and analytical design, we may further gain insight into the dynamics of inter-individual interaction through eye-contact and inter-brain synchronization. To explore the temporal dynamics of inter-brain synchronization, we are currently conducting a hyperscanning simultaneous EEG-fMRI recording that could integrate the merits of the two neuroimaging methods (Koike et al., 2015). As the present study demonstrated the efficacy of using Akaike causality analysis to evaluate dynamic mutual interaction, future studies applying this method to EEG data in ecological settings of normal and diseased populations are warranted."

The authors also recommend that future studies could adapt their methods to "reveal the mechanism underlying the means by which two brains are wired through an eye-to-eye communication without any conscious awareness."

Despite the above-mentioned limitations, this research could prove to be groundbreaking. In my opinion, the most notable aspect of the latest mutual gaze findings (Koike et al., 2019) is that this eye contact research advances our understanding of a previously underappreciated non-motor function of the human cerebellum during face-to-face social interactions.

The authors conclude, “These findings underscore the notion that real-time eye contact generates an emergent property of shared attention, which is mediated by a cerebello–cerebral network inclusive of the limbic mirror system.”