Does your brain burn?

Image credit: OpenAI

Have you ever felt that your brain is fried after having a ‘heated’ discussion with someone about something you were very passionate about or when someone is boring you with their lecture? In Hindi, we even say that the boring person had ‘cooked’ us (literally translated). Where do these words come from? Is it just a random metaphor?

For this, we need to understand that the brain, like any other part of our body, requires energy to function. Just like how we say that we can’t even lift our finger when we are tired, it gets difficult for us to think straight when we are tired as well. But how much energy does our brain use up in a day?

The brain is responsible for most of our bodily functions. It is part of the nervous system, which also includes the spinal cord and other nerves that run almost throughout the body. It seems to have evolved more than three hundred million years ago in ancestors of all animals with bilateral symmetry. The brains of brain-containing animals are also symmetrical bilaterally. This includes the human brain.

The brain is made up of the famous neurons, which make up about half of all the cells in humans, and other types of cells collectively called glia. The neurons are the ones that do all the work of carrying the information in the form of electric impulses, not unlike wires in our homes. The glia protects the neurons from everything, including insulating them so that they don’t short circuit among themselves, cleaning up the mess around, and also supporting the neurons from literally collapsing upon themselves. There are about 100 billion neurons in an adult human brain, and just as many glia, so if you keep your hands on your head, you can imagine a cool 200 billion cells between your hands.

A general assumption that we have is that the human brain uses up roughly 20 percent of the energy the whole body consumes. This is surprising because the brain, in terms of weight, is only about 2-3 percent, and in terms of volume, is not even 2 percent of the human body. So for such a comparatively small organ, it uses up a lot of energy.

An average active human adult male is said to require 2250 Cal per day. If the brain uses up twenty percent of this, that comes up to 450 Cal per day. This amount of energy is equivalent to the energy content of about 53 milliliters of diesel.

Doesn’t seem like a lot, does it? If you were driving a car, a Maruti Suzuki Alto 800 diesel model for example, and for a weird reason you ask the diesel station guy to give you 53 ml of diesel. How far can you drive your car with this fuel?

The Maruti Suzuki Alto 800 diesel car is reported to have an average mileage of 28 kmpl. Under hypothetical ideal conditions, the car can travel about 1.5 kilometers with 53 ml of diesel, which can contain the same amount of energy as 450 Cal, the energy an average human male brain spends per day.

In a year, that will be a whopping 541 kilometers. That means that with the amount of energy your brain spends in a year, you can drive from the Gateway of India in Mumbai, all the way to Panjim in Goa and still have some more energy to spare.

That is a lot of energy.

But let’s get back to the amount of energy spent in a day to make things easier for us to understand. The brain, in a day, uses the energy equivalent to the energy used for driving an average car for a kilometer and a half. Where does all that energy go? If you have ever been near a car engine after it stops, you’ll notice how hot it is. Although driving it slow enough to travel such a short distance in a whole day will probably not heat up the car engine so much, the point is that there is the heat given off by it. Does that mean that the brain also produces heat in the same way?

Turns out, it does.

The brain receives up to 20 percent of the total cardiac output of the body and has more blood vessels per unit volume than any other part of the body. The blood not only carries the nutrients to the brain but also carries away the waste from the brain so that it can keep the temperature stable, without which the brain can run a very real risk of heating up beyond control.

Despite all this, the brain reportedly is at a higher temperature than the rest of the body, but by how much? In a published study, researchers measured the temperature of the brain by drilling a hole through the skull, called a borehole, and inserting a thermistor directly into the brain. They found that the brain was at 38.5 °C in normal human beings under normal circumstances, and the deeper regions of the brain can even go up to 40 °C. Compare that with the temperatures we take with an under-the-tongue thermometer and you’ll realize that this is like having a high fever constantly in your head. People who had suffered from traumatic brain injury displayed brain temperatures of up to 42.3 °C.

The image shows the temperatures recorded in different parts of the human brain at different times in a full 24-hour cycle in both males and females. Taken from the video abstract of Rzechorzek et. al, Brain, 2022.

But there are not many studies on human brains (understandably so with such techniques). But we know from animal studies that behavioral stimuli can increase the temperature of the brain. We also know that the energy usage of the brain increases with increased cognitive exercise. Therefore, maybe there is merit in thinking that the brain is ‘cooked’ when someone is boring you to no end.

But how then do we reduce the cooking of the brain? Many studies have backed traditional methods such as meditation and aerobic exercises, or cardio as we generally call it, to cool down the brain. Endorphins released by the pituitary gland during exercise have been shown to be the most potent regulator for brain ‘cooling’. The exact reasons for the cooling down of the brain due to meditation are currently unknown. However, speculations range from suggestions that the brain activity reduces due to the disengagement of the brain circuitry from stray tasks, thereby reducing the total number of electrical impulses firing in the brain; to the suggestion that the brain is closer to a sleep state, which is when most of the waste removal of the brain happens.

Unfortunately, to get back to our original question, when someone is boring us, it is not really practical to start meditating in front of them, and we are even less likely to start doing exercises.  But there is another simple and common thing we do, mostly unintentionally, that can help. The trouble is, it is considered disrespectful. The act is yawning. We naturally yawn when we are bored, and that is our body’s way of reducing brain strain. Research on how yawning helps reduce brain temperature is still ongoing, all we know is that it indeed does.

So, perhaps next time someone is ‘cooking’ your brain, maybe turn away from them or duck under the table, and yawn a little. It sure is good for you.

Aditya Undru
Aditya Undru
Aditya Undru is a graduate student at CSIR-CCMB with Dr. Arvind Kumar. He is a neuroscientist and bioinformatician currently studying the protective effects of a little-known phenomenon called hypoxic preconditioning using Zebrafish as a model organism, where he uses proteomics and transcriptomics to understand the molecular mechanisms involved. He is also a writer, poet, storyteller, singer, cyclist and amateur historian. He can be contacted at, on Instagram as @hyderabadicyclist or connected on LinkedIn as adityaundru.