100 Fun Facts About The Brain

What are the three main parts of the human brain?

Cerebrum, brainstem, cerebellum. The cerebellum takes up only about a tenth of the brain's volume, yet it holds more neurons than the rest of the brain combined.

Roughly how much does an adult human brain weigh?

About 1.3 kg. Albert Einstein's brain weighed 1,230 grams, a little lighter than the average man's.

About how many neurons are in the human brain?

86 billion. Suzana Herculano-Houzel reached the figure by dissolving donated brains into a 'soup' and counting the nuclei; textbooks had long said 100 billion.

The brain uses about what share of the body's energy at rest?

20%. Hard thinking barely raises it: the brain burns nearly as much energy at rest as it does on a difficult problem.

What is the main fuel the brain normally runs on?

Glucose. The brain needs a constant supply of it from the blood, which is why a steep fall in blood sugar can cause loss of consciousness.

The brain's four main lobes take their names from what?

Skull bones. Each lobe is named for the bone lying over it, but the match is only rough: the lobes are divided by grooves in the brain's surface, not by the seams of the skull.

Which lobe is dedicated to vision?

Occipital. Damage to this lobe on both sides can cause cortical blindness, in which the eyes are healthy but the brain can no longer see.

Parkinson's disease follows the loss of brain cells that make which chemical messenger?

Dopamine. The cells that make it sit in a region called the substantia nigra, and movement symptoms appear only after more than half of them are already lost.

What is the outer grey-matter layer of the cerebrum called?

Cerebral cortex. It is only 2 to 4 mm thick, so it folds deeply to fit more grey matter inside the skull.

What are the ridges and grooves on the brain's surface called?

Gyri and sulci. Mice and rats have none: their brains stay smooth, which in a human is a rare and serious condition called lissencephaly.

What does the corpus callosum do?

Connects the two hemispheres. Kim Peek, the savant who inspired Rain Man, was born without one, and some people who lack it show no detectable problems at all.

What does the Latin name 'cerebellum' mean?

Little brain. The name undersells it: scans show that its tightly pleated surface, unfolded, has almost 80 percent as much area as the surface of the cerebrum.

The cerebellum is best known for its role in what?

Motor coordination. It does not start a movement but fine-tunes its timing and precision, so damage leaves a person able to move yet clumsy and unsteady.

Which three structures make up the brainstem?

Midbrain, pons, medulla. The pons, Latin for bridge, earns its name as the main link between the cerebellum and the rest of the brainstem.

The centres that control breathing and blood pressure sit mainly in which brain structure?

Medulla. It sits where the brain meets the spinal cord and works without conscious effort, which is why you keep breathing in your sleep.

The hippocampus takes its name from its resemblance to which animal?

Seahorse. The 16th-century anatomist Arantius, the first to describe it, wavered between a seahorse and a white silkworm; the seahorse stuck.

The hippocampus is most important for which function?

Consolidating long-term memory. London taxi drivers, who must memorise the city's streets to earn a licence, were found to have a larger rear hippocampus than other people.

The amygdala is most associated with processing which of these?

Fear and emotion. A woman known as S.M., whose amygdalae were destroyed by a rare disease, showed no fear when handed snakes or led through a haunted house.

Which structure links the nervous system to the endocrine system via the pituitary?

Hypothalamus. It is also the body's thermostat: a fever begins when it resets itself to a higher temperature.

Which gland produces melatonin, the hormone that helps regulate sleep?

Pineal gland. Named from the Latin for pine cone, after its shape, it makes melatonin in darkness, and light reaching the eyes suppresses it.

Which philosopher called a small gland deep in the brain 'the principal seat of the soul'?

René Descartes. His reason was that he could find no other part of the brain 'which is not double', so this single gland had to be where our thoughts come together.

What are the three protective membranes around the brain and spinal cord called?

Meninges. When an infection inflames these membranes the illness is meningitis, whose warning signs include a severe headache and a stiff neck.

What does 'dura mater', the name of the brain's outermost membrane, mean in Latin?

Tough mother. The Latin is a medieval translation of an Arabic phrase, 'thick mother of the brain'; Arabic often uses family words for the relationships between things.

The middle membrane around the brain is named for its resemblance to what?

A spider web. It is the arachnoid mater, from the Greek for cobweb, after the fine web-like fibres that cross the fluid-filled space beneath it.

Why can surgeons operate on the brain while the patient is awake and talking?

Brain tissue has no pain receptors. Keeping the patient awake lets the surgeon test each spot first and steer around any area where speech or movement falters.

The fluid-filled chambers deep in the brain, where cerebrospinal fluid is made, are called what?

Ventricles. If the fluid cannot drain away it builds up and the chambers widen, pressing on the brain, a condition called hydrocephalus.

Neurosurgeon Katrina Firlik likened the feel of the living brain to what?

Soft tofu. She rejected her colleagues' comparison to toothpaste, noting that a cut cube of brain holds its shape, 'although not quite as well as tofu'.

The blood–brain barrier is formed by the tightly sealed walls of which vessels?

Capillaries. Their wall cells are joined so tightly that germs in the blood are kept out of the brain, but so are most drugs, a major hurdle in treating brain diseases.

Which scientist, who coined 'magic bullet', found that some injected dyes failed to stain the brain?

Paul Ehrlich. He put it down to brain tissue having little affinity for those dyes; Edwin Goldmann later showed that dye injected into the spinal fluid stained the brain after all.

What is the fatty material that insulates axons and speeds up nerve impulses?

Myelin. In multiple sclerosis the immune system attacks it, and the stripped nerve fibres can no longer carry their signals properly.

What are the gaps between the insulating segments on an axon called?

Nodes of Ranvier. The nerve impulse jumps from one gap to the next instead of travelling along the whole fibre, which makes it much faster.

What is the electrical signal a neuron fires called?

Action potential. It is all-or-nothing: a stronger stimulus does not make a bigger spike, because the neuron either fires fully or not at all.

What is the junction where one neuron passes a signal to another cell called?

Synapse. These junctions grow stronger the more they are used and weaker when they are not, which is thought to be how the brain lays down memories.

Which of these animals have no neurons at all?

Sponges and placozoans. Jellyfish have no brain either, yet they do have neurons, linked in a loose nerve net that lets them sense light and smell.

What are the brain's supportive non-neuron cells called?

Glia. The name is Greek for glue, from the old idea that they merely held neurons together; they are now known to feed, insulate and clean up after them.

In most people, the left hemisphere of the brain is dominant for which ability?

Language. That is why a stroke on the left side of the brain is the kind most likely to leave a person struggling to speak or to follow words, a condition called aphasia.

Broca's area, linked to speech production, is in which lobe?

Frontal. Paul Broca found it in 1861 at the autopsy of a patient who could say little more than the syllable 'tan', and who went down in history by that name.

Which railroad foreman survived an iron rod through his skull in 1848?

Phineas Gage. He lived for nearly twelve more years and kept the metre-long tamping iron as his 'constant companion', taking it with him as far as Chile.

Doctors reported that the 1848 tamping-iron accident mainly changed what about its survivor?

His personality. The once capable foreman changed so much that he could not go back to his old job, though later research suggests he recovered more than the legend allows.

The famous amnesia patient 'H.M.' had brain surgery in 1953 to treat which condition?

Epilepsy. The operation eased his seizures but left him unable to form new memories, and scientists went on studying him for five decades.

Hans Berger's 1924 recording of a human brain's electrical waves was the first of which test?

EEG. Berger took up brain research hoping to explain telepathy: by his own account, his sister had sensed from miles away an army accident that nearly killed him.

The brain waves that dominate when you relax with your eyes closed are called what?

Alpha. They were the earliest brain rhythm recorded in humans, by Hans Berger in the 1920s, and he found that they fade as soon as the eyes open.

Which two scientists shared the 1906 Nobel Prize for work on the nervous system?

Golgi and Ramón y Cajal. They never agreed: Cajal used Golgi's own silver stain to show that neurons are separate cells, while Golgi insisted nerves formed one continuous net.

Which ancient thinker placed intelligence in the heart and saw the brain as a cooling organ?

Aristotle. He treated the brain as a mere radiator for the body's heat; some five centuries later the physician Galen, dissecting animal brains, put the mind back in the head.

Which Greek physician is credited with On the Sacred Disease, the text that traced a 'divine' illness to the brain?

Hippocrates. Written around 400 BC, the treatise argued that the so-called sacred disease was no more divine than any other and had a natural cause in the brain.

What 19th-century pseudoscience mapped personality onto bumps of the skull and cortex?

Phrenology. Its skull readings were wholly discredited, yet founder Franz Joseph Gall's hunch that different mental functions sit in different parts of the brain had a basis in reality.

A long-running myth claims that people use only what share of their brains?

10 percent. Scans show the opposite: nearly every region is active over the course of a day, and many stay busy even during sleep.

What did scientists find inside the skull of a man killed by Vesuvius in AD 79?

A brain turned to glass. A 2025 study found that a brief, scorching ash cloud heated it to extreme temperatures and then passed so quickly that it set as glass, the only such case known.

What is the glymphatic system thought to do, especially during sleep?

Clear metabolic waste from the brain. In mice the clear-out speeds up during sleep and carries off beta-amyloid, the protein that builds up in Alzheimer's disease.

Which 1942 science-fiction novel is about an isolated organ kept alive in a tank?

Donovan's Brain. In Curt Siodmak's novel the brain of a dead millionaire turns the tables, taking telepathic control of the scientist who keeps it alive; it was filmed three times.

Whose brain did pathologist Thomas Harvey remove at autopsy in 1955 and keep for decades?

Albert Einstein's brain was cut into about 240 blocks, and a journalist found the pieces in Harvey's possession in 1978. Harvey had also removed the physicist's eyes.

The 'brain-eating amoeba' Naegleria fowleri usually gets into a swimmer's body by which route?

The nose is its doorway: inhaled with warm fresh water, the amoeba follows the olfactory nerve up into the brain. Rare cases have come from rinsing the sinuses with a neti pot.

Which sea animal keeps about two-thirds of its neurons in its arms rather than in its brain?

Octopus arms carry most of the animal's neurons in their nerve cords, so they can move and sense largely on their own without waiting for orders from the central brain.

Which sea giant, the species of Herman Melville's Moby Dick, has the largest brain of any animal?

The sperm whale's brain averages about 7 kilograms, the largest known of any modern or extinct animal. One such whale sank the whaleship Essex, the true story behind the novel.

A 1993 study sparked the popular belief that listening to which composer makes people smarter?

Mozart's sonata for two pianos gave listeners only a 15-minute lift on spatial puzzles, yet in 1998 Georgia's governor budgeted for a classical recording for every newborn.

Which dinosaur was once wrongly said to have a 'second brain' in its hips?

Stegosaurus has a large canal in its hip region that could hold something 20 times bigger than its famously small brain, which is what inspired the myth.

Which operation, performed on President Kennedy's sister Rosemary, won its inventor a Nobel Prize?

Lobotomy earned Portugal's António Egas Moniz a share of the 1949 prize, an award critics have asked to be rescinded. Rosemary Kennedy was permanently incapacitated by hers.

Which of these water-loving mammals sleeps with only one half of its brain at a time?

Dolphins let one side of the brain sleep while the other stays alert, so they can keep surfacing to breathe and watching for predators.

Which farm animal, nicknamed Mike, lived for 18 months in the 1940s after its head was cut off?

A chicken can run its basic reflexes from the brain stem, and the axe missed most of Mike's. His owner fed him with an eyedropper and took him on tour with sideshows.

Scans showed that mastering 'the Knowledge' physically reshapes the brains of which London workers?

Taxi drivers spend years learning London's street layout, and Eleanor Maguire's studies of them won a 2003 Ig Nobel Prize for showing their brains were 'more highly developed'.

The FAST checklist (face, arms, speech, time) helps bystanders spot which medical emergency?

Stroke signs include a drooping face, a weak arm and slurred speech. British doctors and ambulance crews devised the acronym in 1998 to get patients to clot-busting drugs within three hours.

Which illness, first described by a German psychiatrist in 1906, is the commonest form of dementia?

Alzheimer's disease is named after Alois Alzheimer, whose first case was a woman of fifty he called Auguste D. Its usual early sign is difficulty remembering recent events.

What is the name for the vivid feeling that an amputated arm or leg is still attached to the body?

Phantom limb sensations affect most amputees. The name was coined in 1872 by physician Silas Weir Mitchell, who wrote of a 'sensory ghost' of the missing part.

Which fictional detective boasts of solving crimes with the 'little grey cells' of the brain?

Hercule Poirot, Agatha Christie's Belgian sleuth, uses the phrase from his debut in The Mysterious Affair at Styles, alongside his other motto, 'order and method'.

ALS, the nerve disease Stephen Hawking lived with, is named in America after which baseball star?

Lou Gehrig took himself out of the Yankees lineup in 1939 as the illness set in. Weeks later he told a packed stadium he was the 'luckiest man on the face of the earth'.

'Mad hatter disease' struck felt-hat makers who breathed in the vapour of which metal?

Mercury, in the form of mercuric nitrate, was used to turn animal fur into felt, and its fumes attacked the workers' nervous systems. The illness was also nicknamed 'hatter's shakes' and 'Danbury shakes'.

Rats carrying the brain parasite Toxoplasma gondii stop avoiding the urine of which predator?

Cats are the only animals in which the parasite can reproduce sexually, so a rat that no longer keeps away from them gives it a route back to its breeding ground.

Which extinct human relatives had brains that averaged larger than those of people living now?

Neanderthals had braincases averaging about 1,640 cubic centimetres in males, more than any living human population, though their brains were organised differently.

Which 1999 film about humans kept in pods and fed a fake world echoes the 'brain in a vat' puzzle?

The Matrix is counted among the works inspired by Hilary Putnam's version of the thought experiment, itself an update of a 17th-century philosopher's deceiving 'evil demon'.

Which trait makes some people see colours when hearing sounds, or perceive letters as coloured?

Synesthesia is often traced back to 1690, when John Locke wrote of a blind man who said the colour scarlet was like the sound of a trumpet, though he may have meant it only as a comparison.

A newborn baby's head has soft spots that leave room for the brain to grow; what are they called?

Fontanelles are membrane-covered gaps between the bony plates of the head. They let the head flex on its way through the birth canal, and the one at the front closes over by about 18 months.

Face blindness, the inability to recognise familiar faces, goes by which medical name?

Prosopagnosia was named in 1947 by a German neurologist. One of his patients, shot in the head, could no longer recognise his friends, his family or even his own face.

In which nightly phase are the muscles paralysed while the brain is almost as active as when awake?

REM sleep is nicknamed paradoxical sleep: the body lies paralysed while nerve cells fire about as intensely as in waking life. It is the stage most closely tied to dreaming.

SSRIs, the most widely prescribed antidepressants in many countries, act on which brain chemical?

Serotonin supplies the second S in the name: selective serotonin reuptake inhibitors stop nerve cells reabsorbing the chemical, which gradually changes how the brain signals.

The word 'brainwashing' reached English in 1950 as a direct translation of which country's phrase?

China's term xǐnǎo, literally 'wash brain', was borrowed by journalist Edward Hunter to explain why some American prisoners in the Korean War cooperated with their captors.

Savant Kim Peek, who memorised thousands of books, was the inspiration for which Oscar-winning film?

Rain Man's Raymond Babbitt, played by Dustin Hoffman, was modelled on Peek, who was said to be able to recall the contents of at least 12,000 books.

Mad cow disease, which leaves cattle brains spongy with holes, is spread by what kind of agent?

A prion is a misfolded form of a normal brain protein, not a living germ. People who ate infected beef could develop a human version, variant Creutzfeldt–Jakob disease.

Which operation, perhaps the oldest surgery known, meant cutting a hole in a living person's skull?

Trepanation dates back 7,000 to 10,000 years, and many Stone Age skulls show new bone growing in around the hole, proof that the patient survived.

What is a brain-damaged patient's ability to react to objects they cannot consciously see called?

Blindsight got its name in 1974 from Lawrence Weiskrantz. In one test, a man reached for a target past obstacles on his sightless side without bumping into a single one.

Tying shoelaces without thinking through each step draws on which kind of memory?

Procedural memory stores the routines behind skills from tying shoes to flying an aeroplane, and plays them back automatically, with no conscious effort to recall the steps.

Damage to the movement area in the right half of the brain typically weakens which part of the body?

The left side, because the pathways between brain and body cross the midline. One theory traces the crossover to a twist that the embryo makes very early in its development.

Which part of the body has about 500 million neurons of its own and is nicknamed the 'second brain'?

The gut is lined with a mesh of nerve cells, the enteric nervous system, holding about five times as many neurons as the spinal cord. It governs the churning and secretions of digestion.

Caffeine keeps people alert by blocking brain receptors for which drowsiness-building chemical?

Adenosine builds up the longer a person stays awake, and its receptors respond by increasing drowsiness. Caffeine occupies those receptors, so the tiredness goes unfelt for a while.

Which natural painkillers does the brain produce during hard exercise to dull pain and lift mood?

Endorphins take their name from 'endogenous morphine', meaning morphine from within. They block the perception of pain and boost feelings of well-being.

Which neurologist wrote The Man Who Mistook His Wife for a Hat and the book behind Awakenings?

Oliver Sacks based Awakenings on patients he treated with a new drug in New York; the 1990 film starred Robin Williams and Robert De Niro. His 'Hat' case study even became an opera.

Which Scottish city gives its name to the scale doctors use to grade a patient's level of coma?

Glasgow's university medical school is where Bryan Jennett and Graham Teasdale devised the scale, published in 1974. It scores three things: eye, verbal and movement responses.

Which of the five senses is the only one that does not route its signals through the thalamus?

Smell is the exception: every other sensory system has a relay nucleus in the thalamus that receives its signals and passes them on to that sense's own area higher up.

A single brain cell that fires for just one famous face is nicknamed after which Friends star?

Jennifer Aniston's photo often set off one particular neuron in conscious patients whom UCLA surgeons were treating for seizures, so the team named the cell after her.

The earliest known description of the brain's surface is in a surgical text from which civilisation?

Ancient Egypt's Edwin Smith Papyrus, copied out around 1600 BC, also recognises that an injury to the brain can paralyse another part of the body.

Which inherited illness, known for jerky dance-like movements, killed folk singer Woody Guthrie?

Huntington's disease had already struck Guthrie's mother, who was institutionalised when he was a teenager. He inherited it from her and died of its complications in 1967.

The memoir The Diving Bell and the Butterfly was dictated by blinking by a man with which condition?

Locked-in syndrome leaves the mind intact while most of the body is paralysed. French magazine editor Jean-Dominique Bauby woke in hospital able to blink just one eyelid.

Kuru, a fatal 'laughing sickness' of Papua New Guinea's Fore people, was spread by which practice?

Eating the dead was a funeral rite thought to help free a relative's spirit. The Fore largely gave it up around 1960, years before anyone linked the custom to the illness.

Which brain disease of repeated head blows was first studied in boxers as 'punch-drunk syndrome'?

CTE, short for chronic traumatic encephalopathy, was first described in 1928 by a New Jersey medical examiner who noted the tremors, slowed movement and confusion of veteran fighters.

Which creature with just 302 neurons was the first animal to have its whole nervous system mapped?

A roundworm called Caenorhabditis elegans, a transparent soil dweller about a millimetre long, was also the first multicellular organism to have its whole genome sequenced.

People with the rare Capgras delusion are convinced of what about their closest relatives?

They are impostors, sufferers insist: identical doubles who have taken the place of a spouse, a parent or even a pet. French psychiatrist Joseph Capgras first described it in 1923.

Which Montreal neurosurgeon mapped the brain by probing its surface while his patients were awake?

Wilder Penfield watched how conscious patients responded to each touch of the probe, and from the results drew the 'homunculus', a map of the body as the brain represents it.

Mirror neurons, which fire when acting or just watching, were first recorded in which animals?

Macaque monkeys had electrodes placed in a movement-planning area by a team at the University of Parma, who were studying the cells that control taking hold of an object.

People with aphantasia, a trait named by neurologists in 2015, are unable to do what?

Picture things mentally is what they cannot do, at least at will. A University of Exeter team led by Adam Zeman named the trait from Greek words meaning 'without' and 'image'.

Rats in a famous 1950s McGill experiment kept pressing a lever to deliver what to their own brains?

Electric pulses to a spot called the septal area proved so rewarding that James Olds and Peter Milner realised they had found what were first called the brain's 'pleasure centres'.

George Miller's 1956 paper put the capacity of short-term memory at 'the magical number' what?

Seven, 'plus or minus two', is how the Harvard psychologist's title put it, and the paper is often read as setting the number of items an average person can hold in mind at once.