What does a higher body temperature do to your concentration and memory?
A higher body temperature worsens your working memory and attention, and makes you more impulsive without making you more accurate. Staying cool, especially during mentally demanding tasks, protects your thinking ability.
Heat impairs your thinking in several ways. Exposure to heat stress at an ambient temperature of around 30 °C noticeably worsens working memory and slows reaction times on attention tasks. Heat combined with traffic noise produces the greatest impairment. That pattern has been found repeatedly across many studies.
What happens in the brain is fascinating. Even with a core temperature rise of around 1 °C, the brain becomes less efficient: it has to activate larger areas to complete the same task, while blood flow to the brain actually falls. You react faster, but not more accurately. That speed without any gain in accuracy is a sign of more impulsive, less careful thinking, not of better functioning.
During physical effort in extreme conditions, such as military flight operations, body temperature rises by an average of 4.41 degrees Fahrenheit to nearly 103 °F. This goes hand in hand with a sharply elevated heart rate and reduced performance on both physical and mental tasks. The higher the temperature, the greater the strain on the brain.
Interestingly, when exercising in the heat, the exact outcome depends on the task. Simpler memory tasks deteriorate earlier and more clearly than more complex tasks, where results remain mixed. This means that 'heat impairs your memory' does not apply equally in every situation, but the overall picture is clear: staying cooler protects your thinking ability.
This answer draws on five studies in people that examined heat exposure experimentally or in real-world settings, including studies involving military crew members, healthy volunteers in a controlled environment, and athletes. The effects on brain activity are the most strongly supported; the effects on memory for more complex tasks are more variable. None of the studies used blinding or a placebo for the temperature manipulation itself, which makes a cause-and-effect relationship plausible but not definitively proven.