How much does the brain weigh?

The average adult human brain weighs 3.5 pounds (1.6kg), which is roughly the weight of a large bag flower.

Can the brain feel pain?

No. The brain itself has no pain receptors.

Do we really only use 10% of our brain?

Nope! Brain imaging shows nearly region is active, often at the same time.

How much energy does my brain use?

About 20% of your body's oxygen and blood. Awake it generates enough energy to power a small light bulb.

Why do smells trigger strong memories?

Smells connect directly to emotion and memory centers and bypass rational bran areas. This is how a scent can instantly transport you.

Can brain lesions change behavior?

Yes! Some lesions make average eaters obsess over gourmet food, which changes cravings and habits.

How big is my brain's wiring?

Your axons and dendrites could wrap around the Earth four times with over 100,000 miles of connections.

30 Mind-Bending Brain Facts Backed by Science (UPDATED)

By Karin Lehnardt, Senior Writer—Reviewed for accuracy by the FactRetriever editorial team

Published June 26, 2017Updated December 23, 2025

The human brain weighs only about three pounds, yet it may be the most complex object in the known universe. Scientists still know more about stars exploding billions of light-years away than they know about the organ inside your skill. Here are the strangest, most fascinating facts for students, teachers, and curious readers of all ages.

You can't tickle yourself
Brain scientists have identified the cerebellum as the part of the brain that prevents us from tickling ourselves. It helps us distinguish between expected and unexpected sensations._[17]
The brain cannot feel pain
The brain does not have any pain receptors and, consequently, cannot feel pain. This is why brain surgery can sometimes be performed on awake patients._[15]
Eyeballs are a direct physical extension of the brain
Your eyeballs are not just connected to your brain; they are made of brain tissue. From an evolutionary and developmental standpoint, the eyeballs are actually outgrowths of the brain. The retina is neural tissue, not skin or muscle. Changes in the retinas can mirror changes happening deep inside the brain._[12]
Deja vu may be a memory timing glitch
Déjà vu (French for “already seen”) has never been fully explained, though some scientists believe that a neurological glitch causes an experience to be registered in the memory before reaching consciousness._[14]
Blackout drinking isn't forgetting--it's never recording
When a person becomes "black-out" drunk, they aren't forgetting what happened. Their brain temporarily loses the ability to make new memories. Events aren't forgotten; they're never stored._[5]
Your brain uses about 20% of the body's energy and oxygen
Although the brain makes up only about 2% of body weight, it consumes roughly 20% of the body's total energy, oxygen, and blood supply, even while resting._[11]
The brain can change and rewire itself
The human brain is not fixed. Through a process called neuroplasticity, it constantly forms new connections, especially during childhood and the teenage years. Learning new skills physically changes the brain._[1]
The brain never stops firing
Even during deep sleep, the brain never stops firing. Electrical signals constantly ripple across neural networks, and scientists can measure this activity using electroencephalography (EEG), which detects tiny voltage changes through sensors placed on the scalp._[14]

The human brain has the consistency of tofu

The human brain is incredibly soft
A human brain feels less like an organ and more soft tofu or gelatin. The brain is 75% water, which immediately makes it far softer. Water allows molecules to move quickly and efficiently, which is necessary for fast neural transmitting._[6]
The brain is one of the fattiest organs
The human brain consists of 60% fat, making it one of the fattiest organs in the body._[11]
Babies start with more neurons than adults
Humans have more brain cells at age two than at any other time of life. Unused connections are later pruned._[6]
Babies can produce every human speech sound.
Infants can initially make sounds from all known languages. As the brain specializes, unused sound patterns disappear._[2]
Chronic stress can damage brain structure
Chronic exposure to stress can overload the brain with powerful hormones that are intended for short-term functions in emergency situations. Long-term exposure has a cumulative effect that alters and even kills brain cells._[14]
Hunger significantly alters brain behavior
When a person diets or deprives himself of food, the neurons in the brain that induce hunger start eating themselves. This “cannibalism” sparks a hunger signal to prompt eating._[11]
Brain lesions can change your cravings
Swiss researchers have discovered that certain types of brain lesions can lead average eaters to become addicted to thinking about and eating gourmet foods._[11]
The sense of smell connects to the part of the brain that also controls emotions and memories.
This is why smells often evoke strong memories._[11]
Seeing "stars" comes from your visual cortex
What appears as random bursts of light when people hit their heads is actually caused by a jolt to the brain cells responsible for vision. Stars most often appear following a blow to the back of the head because that is the location of the visual cortex._[14]
The scientific name for brain freeze
The scientific name for brain freeze is sphenopalatine ganglioneuralgia._[10]
You have enough brain wiring to wrap around the Earth
The total length of the human brain's neural wiring (axons and dendrites) is vast, potentially reaching around 100,000 miles (160,000 km) per person. This means a person's brain has enough wiring to wrap around the Earth about four times._[14]
The surface area rivals a pillowcase
If the human cortex (the outer layer of the cerebrum) were unfolded, it would cover an area roughly the size of a pillowcase._[11]
Your brain cleans itself while you sleep
During deep sleep, the brain's glymphatic system flushes out waste products, including proteins linked to neurodegenerative diseases._[16]
How the brain controls the body: Voluntary and involuntary actions
The brain controls both voluntary actions (like moving your hand) and involuntary actions (like breathing). Reflexes are a special type of involuntary action designed to protect you. The brain is informed after the movement. Some actions can be controlled both ways. For example, breathing is automatic, but you can control it for short periods of time._[3]
Your brain can't truly multitask
What feels like multitasking is actually rapid task switching, which reduces accuracy and increases mental fatigue._[13]
Brain size does not determine intelligence.
Intelligence depends on how brain regions connect and communicate, not just size or weight._[8]
Memories change every time you recall them
Each time a memory is retrieved, it becomes temporarily flexible and may be altered before being stored again, which is a process called reconsolidation._[7]
The brain creates your sense of time
There is no single "time center" in the brain. Time perception changes based on attention, emotion, and brain chemistry._[4]
The brain takes the longest of any organ to develop
It undergoes more structural changes over a longer period of time than any other organ in the body._[9]
Your brain predicts reality more than it reacts to it
Each time a memory is retrieved, it becomes temporarily flexible and may be altered before being stored again. This is a process called reconsolidation._[7]
The Homunculus
Wilder Penfield (1891-1976) created a drawing that became known as a homunculus, which shows what we would look like if our body parts were as big as the brain space they take up. The homunculus has huge eyes, lips, hands, feet, and a tiny chest, little hips, and small shoulders._[14]

A homunculus is a physical representation of the human body located within the brain (Mpj29 - Own work / Creative Commons)

The human brain is both powerful and fragile
The brain is shaped by birth through old age. Despite centuries of study, it remains one the greatest mysteries in science and one of the most fascinating subjects to explore._[6]