Heat disrupts brain function: scientists are beginning to understand why

Heat records broken in Western Europe: in the UK, thermometers reached 36.1°C — the highest temperature ever recorded for June in the entire history of meteorological observations. The perceived temperature reached 39°C. This dangerous wave covered several countries on the continent at once. But its consequences extend far beyond heat stroke and dehydration: neurobiologists and physicians are documenting a significant and still poorly understood effect of extreme heat on brain function — and are beginning to systematically search for answers.

What Heat Does to Cognitive Functions

During heat waves, people concentrate worse, react more slowly, and make mistakes more often when making decisions. One of the first rigorous experiments of this kind was conducted at Harvard in 2018: students living in hot rooms without air conditioning during a heat wave in Boston showed reaction times 13% slower than their peers in air-conditioned buildings — with the same academic workload. The key mechanism of deterioration is sleep disruption.

When nighttime temperature does not drop below 25°C, the body fails to cool down to the level necessary for complete recovery. Slow-wave, or deep, sleep suffers particularly: it is during this stage that the brain clears itself of metabolic waste and transfers information from short-term to long-term memory. After three or four nights without quality sleep, working memory, concentration ability, and the capacity for sound decision-making noticeably deteriorate.

An additional factor is dehydration: loss of even 1-2% of body fluid reduces attention and impairs short-term memory.

Heat and Mental Health

Cognitive effects are only part of the picture. Mental health data are equally concerning:

• During heat waves, the number of emergency hospitalizations with psychotic episodes increases
• Anxiety disorders and depression statistically worsen with chronic overheating
• Several major epidemiological studies have found a link between rising average temperatures and suicide rates
• During extreme heat, crime statistics show increases in cases of aggression and violence
• The most vulnerable are the elderly, patients with chronic diseases, and those without access to air conditioning

However, most of these data are correlational in nature. The direct mechanisms through which heat changes the psyche remain to be established.

Why There Are No Answers Yet

The main difficulty is the multifactorial nature of the impact. Heat affects the brain through several channels simultaneously: body temperature rises, the body loses water and electrolytes, sleep is disrupted, cerebral blood supply changes, and inflammatory response intensifies. Separating these factors under real conditions is extremely difficult — and laboratory experiments cannot fully reproduce multi-day extreme heat. Another problem is geographic gaps. Most major studies have been conducted in temperate climates: the USA, Europe, Japan. Regions chronically suffering from extreme heat — South Asia, West Africa, the Persian Gulf — are studied far less. It is unknown whether the brain adapts to constantly high temperatures and whether such adaptation has limits.

What This Means

Heat waves are becoming longer, more intense, and cover ever larger territories. The cognitive and mental consequences of heat are no longer a peripheral issue, but a distinct medical and social problem. When scientists understand the specific mechanisms, this will change recommendations for employers, urban planners, and healthcare systems — especially in countries where air conditioning remains a luxury.