Why Do We Hurt the Ones We Love? Insights From the Brain

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The harm that people do to others is a scourge, yet intimate partner violence is a particularly detestable and complex phenomenon. Why would individuals hurt those they profess to care for? A new neuroscience study may provide a clue.

Intimate partners are just that, intimate. They share a special bond with us and a closeness that is unique to such relationships. This intimacy is not purely metaphorical, as revealed by a phenomenon called self-other overlap. As our relationship with others grows more intimate, our self-concept begins to incorporate elements of them, merging our self with theirs.

A part of the brain called the medial prefrontal cortex (MPFC) makes this self-other overlap happen. The MPFC lies in the center of your forehead; its lower boundaries exist between your eyes, and its upper boundaries are at the top of your forehead. The MPFC has many functions, but a critical one is that it differentiates the self from others. When the MPFC encounters things that we own, or hears our name, or is asked about our personalities, this registers in the lower part of the MPFC. But when we see images of strangers, or hear their names, or are asked about their personalities, this registers in the upper part of the MPFC. As we become more intimate with others and self-other overlap begins, the MPFC response gradually shifts from the upper parts of this region to lower ones.

To test if this self-other overlap in the brain might help us understand intimate partner violence, we conducted a recent study published in the journal Social Neuroscience. In this study, we recruited 61 college students who were 18 to 22 years old and about 28 percent male. We asked them to complete a battery of questionnaires that included a measure of how many types of intimate partner violence they had perpetrated in their lives (examples: throwing things at their partner, pushing or shoving them, punching or hitting them). These participants then laid down inside an MRI machine. We used the MRI scanner to measure their brain activity while they completed a computer task against a stranger. In this task, they were repeatedly provoked by this stranger, who selected loud and unpleasant noises, which they had to listen to.

We found that individuals who had perpetrated intimate partner violence in their lifetime (approximately 38 percent of them had) exhibited a different brain response to provocation than those who had never perpetrated an act of violence against an intimate partner. Specifically, perpetrators demonstrated an MPFC response that indicated they perceived the stranger as an "other," whereas those who had never harmed their partner had an MPFC response that was closer to the "self."

Although these brain responses were towards strangers and not participants’ intimate partners, we expect that these neural biases might carry over from one person to the next. In this way, individuals who tend to automatically categorize other people as "others" might be more prone to harming them than those who perceive them as closer to the self. This "other bias" may also make it difficult for some individuals to truly connect with their intimate partners, preventing the naturally occurring self-other overlap from ever happening. Without the protective benefits of the self-other overlap, this neural bias may predispose individuals towards intimate partner violence.

These findings, while preliminary and obtained with a small undergraduate sample, suggest that when the brain defaults to "othering" those around us, particularly when we feel provoked by them, we may be at risk for harming those we care about. Attempts at reducing intimate partner violence may be best served by interventions that facilitate self-other overlap between intimate partners, especially during conflict.