The feeling of heat triggers impulsive behavior and irritability

In the summer of 2022, Chicago was ravaged by heat, with hot, sultry days followed by sweltering nights.

In the nation’s third-largest metropolitan area, about 400 residents tracked their moods during a summer when temperatures topped 100 degrees by mid-June. Were they cranky? Acting impulsively? Lancing verbally? Yes, yes, and yes, according to the survey results.

When people felt uncomfortably warm in their homes, they reported an increase in impulsive behavior. In neighborhoods with lower-income households and less tree canopy, residents also found themselves getting angry easily and becoming verbally aggressive.

The researchposted on PsyarXiv preprint server was run by Kimberly Meidenbauer, assistant professor in the department of psychology at Washington State University, with colleagues from the University of Chicago. Her goal: to better understand how heat affects mood and mental health in real-life settings.

Heat waves’ links to antisocial behavior have spawned decades of theories. Psychologists and others have examined the correlation between high temperatures and higher rates of domestic violence, assaults, and hospitalizations for overdoses and suicide attempts.

Despite the social toll, much is still unknown about the impact of heat on emotional well-being, says Meidenbauer. “There honestly hasn’t been much research on this and most of the work has been done in labs with people performing cognitive tasks. I wanted to study this problem with a diverse and representative sample of people in a real environment with a lot of detail.”

Meidenbauer and her team conducted surveys from May through September, analyzing Census tract data for insights into household incomes, neighborhood tree canopy, park access, and the urban heat island effect, in addition to self-reported data. Survey respondents were spread across the Chicago metropolitan area.

The number of people experiencing heat stress at home and reporting impulsive behavior was concerning, she said.

“The idea here is that if you’re more impulsive, you’re more likely to engage in risky behaviors like substance abuse and self-harm. Even after the heat wears off, the impulsiveness seems to linger for a while, which is kind of crazy,” says Meidenbauer.

Heat appears to affect the brain’s prefrontal cortex, which is important for planning, self-control and emotional functioning.

“Some studies show that when exposed to heat, the connectivity of the prefrontal cortex with other important brain areas is disrupted,” says Meidenbauer. “Other studies suggest that when your body is thermoregulating, it uses up resources, which can be cognitively taxing.”

Heat also interacts with many of the psychotropic medications used to treat mental illness, which can be a factor in self-harm, she says. In addition, some forms of aggression have been linked to impulsive behavior.

Meidenbauer says the study results underscore the need for resources to protect people’s mental health during heat waves.

“Looking ahead, we need to focus on infrastructure that can cool things down,” she says. “That includes buildings designed with passive cooling systems and urban green spaces that reduce the heat island effect.”

But in the short term, access to affordable cooling systems will be critical for low-income and at-risk populations, Meidenbauer says.

“The biggest mitigating factor for heat,” she says, “was whether survey respondents had access to air conditioning in their homes and whether they could afford to run it.”