Physiology and Understanding Emotions

This article is authored by Eva Li, Samantha Eisert, and Danny Rahal and is part of the 2020 pre-graduate spotlight week. 

The theory of mind in social cognition is the ability to perceive others’ emotional states and understanding. It is the way humans are able to read the eyes and facial expressions of other humans and make strong assumptions of how they are feeling without ever speaking to them (Flavell, 1999; Premack & Woodruff, 1978). Theory of mind is not fully developed in young children, which is why they do not understand that others have different thoughts, perceptions, or understandings of situations. They struggle to stand in someone else’s shoes, to imagine what life is like through someone else’s eyes, or take on the mental perspective of someone else. For instance, if a young child knows where a toy is, they might think others also know where the toy is—even if others do not have access to this information (Wimmer & Perner, 1983). As kids grow and develop greater cognition, they eventually acquire theory of mind and this may allow them to understand more complicated emotions related to the evaluations of others, such as embarrassment and shame (Misailidi, 2020; Colonnesi, Engelhard, & Bogels, 2010).

Theory of mind is so important for human beings because we live in a complex social environment. Everyday life is filled with social interactions such as cooperation that puts theory of mind to use. When humans cooperate, say sharing food, theory of mind is used to determine the facial expression of a partner in order to decide if their partner is deceiving them (Trivers, 1971). Likewise, it allows people to help each other. If you notice that your friend is sad based on their expression—even without your friend explicitly saying so—you know to offer social support to make them feel better. Adults rely on this skill in everyday tasks and conversations—it can be hard to talk to someone if you do not have a sense of what they already know and how they are feeling emotionally.

However, not everyone shows the same level of theory of mind. In fact, deficits in theory of mind have been linked with disabilities and psychopathology, including autism spectrum disorder and schizophrenia. (Brüne & Brüne-Cohrs, 2006; Couture et al., 2010; Frith & Corcoran, 1996; Sprong et al., 2007; Rosenthal et al., 2019) Emerging evidence from researchers at UCLA suggests that a physiological factor may also be related to theory of mind—inflammation (Moieni et al., 2015). Inflammation is part of the body’s immune process, in which immune cells are sent to a wound to fight infection and help start the healing process. If you scrape your knee, you might notice the skin around the wound becomes red and swollen. The recruitment of immune cells to fight infection and promote healing at the site of injury is called the inflammatory response.

To investigate the relationship between theory of mind and inflammation, researchers injected college students with small amounts of endotoxin (Moieni et al., 2015). Endotoxin is toxin that induces mild inflammation. To ensure that endotoxin–and not simply the act of injection–leads to experimental changes in the participants, the participants were randomly split into two groups: the experimental group, who were injected with endotoxin, and the control group, who were injected with saline. Having a control group makes it possible to compare the results of the two groups to see if endotoxin leads to significant changes in the experimental participants compared to placebo control participants. The study was also double-blind, meaning that neither participants, the experimenters, nor the nurses responsible for the injections knew which solution (endotoxin or saline) was being injected. This way, the researchers could ensure that people involved in the protocol would not unconsciously treat the participants receiving placebo differently from the participants receiving the endotoxin.

First, the researchers needed to ensure that the endotoxin was working properly and was indeed eliciting an inflammatory response. To measure inflammation in the body, blood was also drawn each hour to measure the level of two common proinflammatory cytokines (TNF-α, IL-6), or signaling molecules that are released as part of the inflammation response. The experimental group peaked in these markers two hours after injection. To measure theory of mind, participants were asked to identify the emotion expressed from pictures of only people’s eyes. They completed this task after entering the study and again two hours later, when inflammatory cytokines are highest after the endotoxin injection. This way, the researchers could test whether people showed differences in theory of mind at low and high levels of inflammation. Lastly, the participants were asked to report their feelings of confusion every hour for six hours so that the researchers could assess whether the endotoxin influenced their general cognition.

Indeed, the placebo group performed better on the emotion recognition task the second time—likely because they became familiar with the task—whereas the group that received endotoxin (and consequently had greater inflammation) performed significantly worse on the task the second time. Importantly, these participants did not show increases in confusion at this point in the task, suggesting that inflammation led to worse social processing rather than poorer cognition in general.

This study highlighted one pathway by which inflammation may relate to psychopathology. Greater inflammation can actually reduce one’s sense of theory of mind such that people have more difficulty identifying the emotions of others, which can worsen daily function and social interactions. The researchers also discovered another interesting finding regarding how inflammation relates to depressive symptoms, and we will discuss that finding in another article!


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