98 Fun Facts About The Human Brain

Roughly how many neurons does the human brain contain?

86 billion. Textbooks long quoted a round 100 billion, plus ten times as many support cells, until a 2009 count found about 86 billion neurons and roughly the same number of other cells.

About what share of the body's energy does the brain consume?

20%, more than any other organ uses. Aristotle had it backwards: he placed thought in the heart and took the brain for a device to cool the blood.

About how much does an adult human brain weigh?

1.4 kilograms, or about three pounds. Weight says little about ability: Albert Einstein's brain, weighed after his death in 1955, was on the small side at 1,230 grams.

A neurosurgeon's well-known comparison likens the feel of a living brain to which food?

Soft tofu, the choice of neurosurgeon Katrina Firlik. Some of her colleagues say toothpaste, but she finds that too runny: a cube cut from a living brain more or less holds its shape.

Which three main parts make up the human brain?

Cerebrum, brainstem and cerebellum. The wrinkled cerebrum does the thinking, the brainstem keeps breathing and heartbeat going, and the cerebellum is what you lean on to play the piano or hit a tennis ball.

The four lobes of each hemisphere are named after what?

The skull bones above them. So the names record where each lobe sits, not what it does: nothing in the word 'frontal' tells you that this is the lobe that plans and weighs up choices.

Which lobe of the brain is dedicated to vision?

Occipital. It is the smallest lobe and sits at the very back of the head, about as far from the eyes as it could be, yet damage there can leave a person blind even with healthy eyes.

A stroke in the brain's left hemisphere typically paralyses which part of the body?

The right side. Nearly all the signals between brain and body cross over on the way, so each hemisphere mainly controls the opposite side of the body.

What is the name of the largest bundle of fibres connecting the two hemispheres?

Corpus callosum. When surgeons cut it, the two halves stop sharing what they know: such patients can name an object that one half of the brain has seen, but not one shown only to the other.

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

The brain has no pain receptors. Only the scalp and skull need numbing, so surgeons can keep the patient naming objects aloud to check that they are steering clear of the areas needed for speech.

Why is the brain's outer layer of grey matter so deeply folded?

To pack more surface into the skull. The layer is only about as thick as a stack of two or three dimes, so folding is the way to fit in more of it, and more nerve cells with it.

Which brain chemical, depleted in Parkinson's disease, also drives the brain's reward system?

Dopamine. In Parkinson's the cells that make it die off in a small region called the substantia nigra, and by the time symptoms show most of them are already gone.

The cortex is mapped into about fifty functional regions named after which anatomist?

Brodmann. In 1909 Korbinian Brodmann published a map of 52 numbered areas, told apart purely by how their layers of cells looked under the microscope.

What is the brain's white matter mostly made of?

Insulated nerve fibres, which fill about half the brain's volume. Their fatty coating, myelin, is what looks white; grey matter is grey because its nerve cells lack that insulation.

Which structure deep in the brain is the relay station for nearly all incoming sensory signals?

The thalamus. Only smell bypasses it, and it does more than pass messages along: it helps keep you awake and alert, so severe damage to it can leave a person in a coma.

Which part of the brainstem contains the centres controlling heart rate, breathing and blood pressure?

The medulla, the lowest part of the brainstem. It also fires off the reflexes you never have to think about, such as swallowing, coughing, sneezing and vomiting.

Most vivid dreams happen in which stage of sleep, when the body's limb muscles are switched off?

REM sleep. The brain is almost as busy as when it is awake, so the brainstem switches off the muscles of the arms and legs to stop you acting out your dreams.

Which part of the brain holds most of its neurons while taking up only about 10% of its volume?

The cerebellum, Latin for 'little brain'. About four in five of the brain's neurons are packed into it as tiny granule cells, and damage shows up as clumsy, unsteady movement.

Which structure consolidates short-term memories into long-term ones and supports spatial navigation?

The hippocampus. Its role became clear in 1953, when surgeons removed most of it from a patient known as H.M.: he could still learn new skills but never again formed a lasting memory of events.

Which almond-shaped structure in the temporal lobe is central to processing fear?

Amygdala, from the Greek for almond. A patient known as S.M., whose amygdalae were destroyed by a rare disease, is left almost unable to feel fear at all.

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

The hypothalamus. Tiny as it is, it works as the body's thermostat and alarm clock: it sets temperature, hunger and thirst, and it is what wakes you up in the morning.

Which small organ produces melatonin and was called 'the principal seat of the soul' by Descartes?

The pineal gland, named for its pine-cone shape. It steps up its output of melatonin once the light fades, which is what helps the body wind down for sleep.

What are the three membranes covering the brain and spinal cord collectively called?

Meninges. An infection of them is meningitis, which can come on suddenly and progress fast enough to kill, so doctors treat a suspected case as an emergency.

Which of the three membranes around the brain is the tough outermost layer?

Dura mater, Latin for 'hard mother'. The phrase was translated word for word from Arabic, where 'mother' and 'father' were used for things that stand in a relation to other things.

Which disease, the most common cause of dementia, leaves plaques and tangles of protein in the brain?

Alzheimer's disease. It is named after Alois Alzheimer, the German doctor who in 1906 found the clumps and tangled fibres in the brain of a woman who had died after years of memory loss.

What makes the living brain effectively weigh just a few percent of its true weight?

Cerebrospinal fluid. The brain floats in it, so it bears only a sliver of its own weight, and the same fluid cushions it against knocks.

The temporal lobes hold the brain's primary centre for which sense?

Hearing. The same lobes help turn sound into meaning: damage to one patch of them can leave a person speaking fluently in sentences that make no sense.

The blood–brain barrier remains permeable to which of these?

Alcohol. Small, fat-soluble molecules slip straight through the barrier, which first showed itself when Paul Ehrlich injected dyes that coloured every organ of his animals except the brain.

Which vessels supply blood to the front of the brain?

The internal carotids. At the base of the brain they join the arteries feeding the back in a ring, so if one vessel is blocked, blood can often still get round by another route.

In the great majority of right-handed people, which ability is housed mainly in the brain's left hemisphere?

Language. When surgeons separated the two halves of patients' brains, the isolated right hemisphere proved mute: it could recognise an object but had no way to say its name.

Which frontal-lobe region is linked to speech production?

Broca's area. The surgeon Paul Broca found it in the damaged brain of a patient nicknamed 'Tan', after the one syllable he could still say, although he understood what was said to him.

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

Glia, from the Greek for 'glue'. The pathologist who named them took them for mere packing between the neurons, but they turn out to feed nerve cells, insulate their wiring and keep the tissue in working order.

Which cells form myelin in the central nervous system?

Oligodendrocytes. Each one wraps stretches of dozens of different nerve fibres, and when the immune system attacks that wrapping the result is multiple sclerosis.

What are the electrical signals fired by neurons called?

Action potentials. Each one is all-or-nothing: a neuron cannot send a bigger pulse for a stronger signal, so it sends more of them instead.

Which anatomist showed that separate neurons are the nervous system's basic units, sharing the 1906 Nobel Prize?

Santiago Ramón y Cajal. He proved it with a stain invented by Camillo Golgi, who shared the prize with him while still insisting that the nerves formed one continuous web.

Charles Sherrington introduced which word for the junction between two nerve cells?

Synapse, from a Greek word meaning 'to clasp together'. The name was needed once nerve cells were understood to be separate units, so that every signal has to pass from one cell to the next.

Which test records the brain's electrical rhythms through electrodes placed on the scalp?

EEG, short for electroencephalogram. The psychiatrist Hans Berger made the first human recording in 1924 while searching for a physical basis for what was then called psychic energy.

Alpha brain waves are strongest when a person is doing what?

Resting, eyes shut. The rhythm swells when a relaxed person closes their eyes and fades the moment they open them again.

In 1848, what was driven through Phineas Gage's head, destroying much of his left frontal lobe?

A tamping iron, a rod over a metre long that he used to pack blasting powder. It shot clean through his skull and landed some 25 metres away, yet within minutes he was talking.

Phineas Gage survived his 1848 accident, but friends called him 'no longer Gage' because of a change in what?

His personality. His doctor wrote that the model foreman had turned fitful and foul-mouthed, yet the change may not have lasted: Gage later held down a job driving stagecoaches in Chile.

The patient H.M. lost the ability to form new memories after a 1953 operation meant to cure what?

Epilepsy. The operation did ease his seizures, at a terrible price, and until his death in 2008 he took part in the studies that showed memory has a home of its own in the brain.

António Egas Moniz won a 1949 Nobel Prize for devising which brain operation?

Lobotomy, called leucotomy in the prize citation. It spread widely in the 1940s until it became clear that it could alter a patient's whole character, and it faded once psychiatric drugs arrived.

Which 19th-century pseudoscience tried to map personality onto regions of the skull and cortex?

Phrenology. Its readings of bumps on the head were nonsense, but its central hunch, that different parts of the brain do different jobs, turned out to be right.

Which extinct human relatives had brains at least as large as those of modern humans?

Neanderthals. Their brains were as big as ours and often bigger, in keeping with bodies that were shorter, stockier and more heavily muscled.

The blue whale is the largest animal, but which animal has the largest brain?

Sperm whale. Its brain is more than five times the weight of a human's, yet most of its enormous head is taken up by an oil-filled organ that helps it focus sound.

A concussion is also known medically as what?

A mild traumatic brain injury. The brain usually recovers, but a second blow before it has healed can cause permanent damage or even death.

Marcus Raichle's studies of the resting brain's energy use revealed which network?

The default mode network. It is busiest when you are doing nothing in particular, daydreaming or letting the mind wander, and tends to quieten when an outside task demands your attention.

What is the term for the brain's ability to reorganise itself through growth and new connections?

Neuroplasticity. Scientists once thought it ended with childhood, but the adult brain keeps rewiring too, which is what recovery after an injury depends on.

Whose brain did pathologist Thomas Harvey remove during a 1955 autopsy and keep in jars for decades?

Albert Einstein's brain was cut into about 240 blocks, and for more than twenty years its sections sat in two mason jars inside a cider box.

Egyptian embalmers discarded the brain but left which organ in the mummy as the seat of thought?

The heart stayed in the body because Egyptians believed it did the thinking and feeling, so its owner would still need it in the afterlife.

'Brain freeze' strikes when something cold touches which part of the body, sending pain to the head?

The roof of the mouth is the trigger: blood vessels there are thought to tighten and swell rapidly, and the pain is 'referred' upwards.

Eleanor Maguire's famous scans found the brain's memory region reshaped by the job in which workers?

London taxi drivers must pass the Knowledge, a test of the capital's streets and important buildings. The finding won Maguire a 2003 Ig Nobel Prize.

Single brain cells that respond to one familiar person are nicknamed after which 1990s sitcom star?

Jennifer Aniston's photos made one particular neuron fire in a fully conscious patient in 2005. Another cell answered to Halle Berry, even to her written name.

The 'brain-eating amoeba' Naegleria fowleri infects people when warm water enters which body part?

The nose is its way in: the amoeba follows the smell nerves up into the brain, and the infection kills more than 97% of patients even with treatment.

Which composer's music gave its name to a 1990s claim that listening to it makes people smarter?

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

The fatal brain disease kuru spread among the Fore people of Papua New Guinea through which custom?

Eating their dead relatives was a Fore funeral rite. Women and children usually ate the brain, so at its peak kuru struck them eight to nine times as often as men.

A Norwegian woman's brain injury in a 1941 air raid left her shunned for suddenly speaking with what?

A German accent is how she sounded once she seemed to have recovered: a case of foreign accent syndrome, which usually follows a stroke. Only 62 cases were recorded between 1941 and 2009.

Which Stone Age operation, perhaps the oldest surgery known, cut a hole in a living patient's head?

Trepanation marks 5–10% of all the Neolithic skulls found, from Europe and Siberia to China and the Americas.

The 2014 film Lucy rests on the myth that people use only what share of their brains?

10% is the figure in the myth, but brain scans show that every area is always active, whatever a person is doing.

In the FAST test for spotting a stroke, after face, arms and speech, what does the letter T stand for?

Time is the T because every minute counts: it means time to call emergency services. Callers are also asked to note when the symptoms began, under the slogan 'time is brain'.

Which mood-regulating brain chemical, the target of SSRI antidepressants, is mostly made in the gut?

Serotonin is about 90% gut-made, produced by cells in the gastrointestinal tract, where it regulates intestinal movements.

Which Scottish city names the 3-to-15 scale doctors use to grade consciousness after a head injury?

Glasgow's university was home to neurosurgeons Bryan Jennett and Graham Teasdale, who published the scale in 1974. It scores eye, verbal and movement responses.

Which neurologist wrote the case-study bestseller 'The Man Who Mistook His Wife for a Hat'?

Oliver Sacks saw his title case turned into a 1986 opera by Michael Nyman. His earlier book Awakenings became a 1990 film starring Robin Williams and Robert De Niro.

Which metal used to make felt poisoned hatters' nervous systems, a condition nicknamed 'mad hatter disease'?

Mercury vapour rose from the treated felt in confined workshops. US health officials once estimated that 80% of American felt makers had the tremors.

Which hormone released by the pituitary gland is nicknamed the 'love hormone' for its part in bonding?

Oxytocin takes its name from the Greek for 'swift childbirth', because it drives the contractions of labour.

Which branching extensions of a nerve cell receive signals from other cells and carry them towards the cell body?

Dendrites take their name from the Greek for 'tree': they typically branch profusely and reach a few hundred micrometres from the cell body.

In which disease does the immune system attack the myelin coating of nerves in the brain and spinal cord?

Multiple sclerosis thins or destroys the fatty sheath that helps nerves carry electrical signals. French neurologist Jean-Martin Charcot first described it in 1868.

Which sleep disorder, marked by sudden daytime sleep attacks, follows the loss of orexin-making brain cells?

Narcolepsy can come with cataplexy, in which laughter, anger or surprise makes the muscles suddenly go limp. The lost cells number only about 70,000.

Which term describes losing the ability to produce or understand words after damage to the brain?

Aphasia led actor Bruce Willis to retire in 2022. Its major causes are stroke and head trauma.

The brain's fusiform area, impaired in people with prosopagnosia, specialises in recognising what?

Faces get a dedicated patch on the underside of the temporal lobe, and it activates even in people who have been blind from birth.

Which condition makes some people see colours when they read letters or listen to music?

The earliest recorded case of synaesthesia is credited to John Locke, who in 1690 described a blind man experiencing scarlet at the sound of a trumpet.

Which nerve, the longest of the autonomic nervous system, links the brain to the lungs and digestive tract?

The vagus is Latin for 'wandering', the root of vague and vagabond. It drives the 'rest and digest' response that calms the body after stress.

Which condition, historically called 'water on the brain', is often treated with a shunt that drains excess fluid?

Hydrocephalus can make a baby's head visibly grow, because an infant's skull has not yet fully fused. Many people with shunts live normal lives.

People with Capgras delusion are convinced that someone close to them has been what?

Being replaced by an impostor is the fixed belief, held about a spouse, parent, friend or even a pet. French psychiatrist Joseph Capgras first described it.

In which rare condition, also named after Dr. Strangelove, does one limb seem to act with a mind of its own?

Alien hand syndrome can leave a person using the good hand to restrain the other. In the film, Peter Sellers's Dr. Strangelove cannot stop his arm giving a Nazi salute.

Which condition left Jean-Dominique Bauby dictating 'The Diving Bell and the Butterfly' by blinking one eyelid?

Locked-in syndrome followed his 1995 stroke. An assistant recited the alphabet until he blinked at the right letter, three hours a day for two months.

Which brain cells, first recorded in macaques in Parma, fire both when acting and when watching the same action?

Mirror neurons turned up while Giacomo Rizzolatti's team was studying cells that control hand and mouth actions, such as taking hold of an object.

What name did neurologist Adam Zeman's team coin in 2015 for being unable to picture images in the mind?

Aphantasia was first described by Francis Galton in 1880, then went largely unstudied until a man told Zeman he could no longer visualise after minor surgery.

Which star-shaped support cells in the human brain help maintain the blood–brain barrier?

Astrocytes also fill the space left by an injury, forming a scar, and one study counts them as the brain's most numerous cell type.

Which arterial loop at the base of the brain lets blood reroute when one supply vessel is blocked?

The circle of Willis is named after Thomas Willis, a 17th-century English physician. Its built-in redundancy can often keep the brain supplied.

Which most abundant excitatory neurotransmitter in the nervous system also gives savoury foods their umami taste?

Glutamate was pinned down as a flavour in 1908, when Kikunae Ikeda evaporated kombu seaweed broth and tasted the brown crystals left behind.

Which scanning method maps brain activity through changes in blood flow and oxygen, using no ionising radiation?

Functional MRI relies on a signal discovered by Seiji Ogawa in 1990: when a brain area is in use, more oxygen-rich blood flows to it.

Caffeine keeps people alert by blocking the brain's receptors for which chemical that builds up while awake?

Adenosine builds through the waking hours until the need to sleep takes over. Caffeine has a similar three-dimensional shape, so it fits and blocks the same receptors.

Which slow, high-amplitude brain waves dominate the deepest stage of non-dreaming sleep?

Delta waves were first described in the 1930s by William Grey Walter, who went on to use them to locate brain tumours.

A lack of which B vitamin causes Wernicke–Korsakoff syndrome, a memory-wrecking brain disorder of heavy drinkers?

Thiamine is vitamin B1. People with the syndrome often confabulate, generating fabricated explanations to cover the gaps in their memory.

Which infectious agents, made only of misfolded protein, cause Creutzfeldt–Jakob disease and 'mad cow disease'?

Prions are so stable that they resist the chemical and physical treatments used to destroy other germs. Stanley Prusiner won the 1997 Nobel Prize for his research on them.

Hodgkin and Huxley worked out how nerve impulses travel using the giant nerve fibre of which sea animal?

Squid evolved a giant nerve fibre, up to 1.5 mm across, to speed their jet-propelled escape response. The experiments won Hodgkin and Huxley a Nobel Prize.

An autopsy showed that actor Robin Williams had been living with which progressive brain disorder?

Lewy body dementia had been misdiagnosed as Parkinson's while he was alive. Doctors described the damage as among the worst they had seen.

Which embryonic structure, normally closed by the fourth week of pregnancy, develops into the brain and spinal cord?

The neural tube closes at both ends during that week, and when the openings fail to seal the result can be spina bifida or anencephaly.

Which darkly pigmented structure in the midbrain progressively loses its neurons in Parkinson's disease?

The substantia nigra is Latin for 'black substance': high levels of a pigment called neuromelanin make parts of it visibly darker than their neighbours.

Which technique lets neuroscientists switch chosen brain cells on and off using pulses of light?

Optogenetics took off after a single gene from a green alga was shown to make cells respond electrically to light.

Which fluid network clears waste products from the brain, by most accounts working hardest during slow-wave sleep?

The glymphatic system was named for doing the job that lymph vessels do elsewhere in the body, and its flushing may help explain why sleep feels restorative.

Which scientist won a 1981 Nobel Prize for 'split-brain' studies of patients with surgically separated hemispheres?

Roger Sperry had first shown in cats that the left and right halves of a divided brain could each learn and remember a different thing.

Which Montreal neurosurgeon mapped the brain's 'homunculus' by stimulating conscious patients with electrical probes?

Wilder Penfield kept patients awake under local anaesthetic and watched their responses. A Canadian TV vignette made one patient's line famous: 'I can smell burnt toast.'

Which Italian biologist invented the 'black reaction', an 1873 silver stain for nerve tissue still named after him?

Camillo Golgi made the discovery in a simple laboratory he had set up for himself in a refurbished hospital kitchen.

Which Canadian psychologist's 1949 theory of learning is summed up as 'neurons that fire together, wire together'?

Donald Hebb set the idea out in The Organization of Behavior, a book arguing that behaviour could only be explained in terms of brain function.

British musician Clive Wearing was left with a memory span of seconds after which virus attacked his brain?

Herpes simplex encephalitis struck in 1985, yet he could still play complex piano pieces and conduct a choir. His diary fills with entries announcing that he is finally awake.

Eric Kandel won a 2000 Nobel Prize for showing how memories are stored, using which simple sea creature?

A sea slug called Aplysia has only about 20,000 neurons, which makes it a favourite of neuroscientists. Kandel studied how its gill-withdrawal reflex changes with learning.