How Much Energy Does Thinking to Take? 2023

After a long day of work or study, your brain may feel exhausted. Is mental athletics more energy-intensive than watching TV?
Our brain’s nerve cells are the key to answering this question. ATP, made from sugar and oxygen, powers our brain cells.

Oxygen is easier than sugar to track brain energy consumption.

Despite weighing only 2%, the brain consumes 20% of the body’s oxygen.

An average adult uses 0.3 kilowatt hours (kWh) per day, more than 100 times the average smartphone. It’s 260 calories or 1,088 kilojoules (kJ) each day (an average adult consumes 8,700 kJ).

What’s our proof?

British researcher David Attwell and colleagues evaluated oxygen consumption in rat brain slices in 2012.

They found that 25% of energy is required for housekeeping, including cell wall upkeep, and 75% for information processing, like computing and neural signal transmission.

We can track oxygen since brain activity requires more oxygen, but we can’t monitor brain energy usage in people.

A capnography gadget measures CO2 levels in a tube to track our bodies’ oxygen use. Non-invasive, this requires masks.

Challenges require extra oxygen for our brains. It’s engineering/pexels

Mental load—such as mental arithmetic, reasoning, or multitasking—is associated to increased oxygen demand (measured by co2 emission).

The increased oxygen use may be attributed to the body reacting to an emotional, stressful event rather than cognitive activity.

Is brain oxygen use measurable?

It’s complex. Brain activity increases blood oxygenation. Region-specific oxygen-rich blood may be directed to activated neurons with micrometre precision.

MRI, a radiation-free technology, may assess brain activity indirectly by weakly attracting blood and oxygen to magnetic fields.

Unfortunately, MRI cannot tell us how much brain energy different mental processes use. MRIs can only measure relative brain activity and energy usage.

However, since our brain is continuously active, it needs energy. We process lots of information even in idle-mind conditions.

We don’t spend our days in a dark floating tank, so sensory input is constant.

Second, even while we’re doing nothing, we’ll think about the past and future.

Last, our emotions—even small ones like tranquility or uncertainty—are brain products and require energy.

Brain activity rises how much?

Pay attention. MRI studies suggest that actively studying moving things boosts visual cortical activity by 1%.

The visual cortex, which makes sense of what we see, is only 18% of the brain’s occipital lobe.

Visual information reduces auditory activity, so we use less energy processing sounds. Auditory processing reduces visual processing activity.

The whole-brain cost of visual attention is presumably mitigated by auditory processing savings.

Focusing on diverse activities makes our brain trade-offs. shutterstock
In conclusion, mental activity increases energy use. The increase is small, region-specific, and generally countered by energy decreases elsewhere.

Why do we tire after mental exertion?

It’s probably mental tension. Complex mental tasks are emotional and activate our sympathetic nervous system, causing mental and physical tiredness.

The good news is that mental activity doesn’t sap brain energy. However, pace yourself to avoid mental overload, tension, and tiredness.