What happens in your brain when you get a fever?

Updated

The hypothalamus resets the body's thermostat higher, the brainstem triggers shivering, the insula makes you feel chills, the anterior cingulate creates malaise, and the prefrontal cortex causes fatigue.

Hypothalamus, Brainstem, Insula, Anterior Cingulate Cortex, Prefrontal Cortex lit up on the Brain Atlas 3D brain: what happens in your brain when you get a fever
Figure. The brain regions that light up when you get a fever, in order: Hypothalamus (reset thermostat), then Brainstem (heat generation), then Insula (feeling chills), then Anterior Cingulate Cortex (malaise and aches), then Prefrontal Cortex (sick and tired).

Watch it light up on the 3D brain

Brain regions that light up

OrderRegionWhat it does here
1HypothalamusThe hypothalamus detects immune signals and raises the body's temperature set point.
2BrainstemThe brainstem carries neural commands that cause shivering and vasoconstriction.
3InsulaThe insula integrates body sensations, creating the feeling of chills despite rising temperature.
4Anterior Cingulate CortexThe anterior cingulate cortex processes the discomfort and pain associated with fever.
5Prefrontal CortexThe prefrontal cortex shows reduced activity, causing fatigue, poor concentration, and apathy.

1. Hypothalamus: reset thermostat

Step 1 of what happens in your brain when you get a fever: Hypothalamus lit on the Brain Atlas 3D brain
Figure 1. Hypothalamus, reset thermostat: The hypothalamus detects immune signals and raises the body's temperature set point.

Cytokines released during infection trigger the hypothalamus to produce prostaglandins, which shift the thermoregulatory set point upward. This makes the body think it is too cold even when temperature is normal. The hypothalamus then initiates heat-generating responses to reach the new higher set point.

2. Brainstem: heat generation

Step 2 of what happens in your brain when you get a fever: Hypothalamus, Brainstem lit on the Brain Atlas 3D brain
Figure 2. Brainstem, heat generation: The brainstem carries neural commands that cause shivering and vasoconstriction.

Signals from the hypothalamus activate brainstem centers that increase muscle tone and cause shivering, as well as constrict skin blood vessels to conserve heat. This raises core body temperature to match the new set point. The brainstem also coordinates sweating inhibition until the fever breaks.

3. Insula: feeling chills

Step 3 of what happens in your brain when you get a fever: Hypothalamus, Brainstem, Insula lit on the Brain Atlas 3D brain
Figure 3. Insula, feeling chills: The insula integrates body sensations, creating the feeling of chills despite rising temperature.

As the body heats up, the insula receives interoceptive signals from skin and internal organs. Because the set point is higher than actual temperature, the insula interprets the discrepancy as feeling cold, producing chills. This subjective experience motivates behaviors like seeking warmth or blankets.

4. Anterior Cingulate Cortex: malaise and aches

Step 4 of what happens in your brain when you get a fever: Hypothalamus, Brainstem, Insula, Anterior Cingulate Cortex lit on the Brain Atlas 3D brain
Figure 4. Anterior Cingulate Cortex, malaise and aches: The anterior cingulate cortex processes the discomfort and pain associated with fever.

Fever often brings headache, muscle aches, and general malaise. The anterior cingulate is part of the brain's pain matrix and becomes active during these unpleasant sensations. It also contributes to the motivational aspect of sickness, making you want to rest and withdraw from activity.

5. Prefrontal Cortex: sick and tired

Step 5 of what happens in your brain when you get a fever: Hypothalamus, Brainstem, Insula, Anterior Cingulate Cortex, Prefrontal Cortex lit on the Brain Atlas 3D brain
Figure 5. Prefrontal Cortex, sick and tired: The prefrontal cortex shows reduced activity, causing fatigue, poor concentration, and apathy.

Fever triggers sickness behavior, which includes lethargy and cognitive slowing. The prefrontal cortex, responsible for executive functions, is affected by inflammatory signals, leading to reduced motivation and difficulty focusing. This is adaptive: it conserves energy for the immune response.

Good to know

  • Fever is typically defined as a core body temperature above 38°C (100.4°F).
  • Prostaglandin E2, produced in the hypothalamus, is a key mediator of the febrile response.
  • Antipyretics like ibuprofen work by blocking prostaglandin synthesis, lowering the set point.

Fever vs. Hyperthermia

In fever, the hypothalamus actively raises the set point, so the body generates heat until it reaches the new target. In hyperthermia (e.g., heat stroke), the set point remains normal but heat production or exposure overwhelms cooling mechanisms. The brain's response differs: hyperthermia does not involve the same prostaglandin-mediated set point shift.

Test yourself

  1. Which brain region acts as the body's thermostat during a fever?

  2. What causes the sensation of chills during a fever's rising phase?

  3. How do antipyretic drugs reduce fever?

0 of 3 answered · 0 correct

Simplified: many regions work together at once, and this shows the main players in the order they act.