98 Fun Facts About Neuroscience

Roughly how many neurons does the adult human brain contain?

86 billion: a 2009 count that replaced the round 100 billion textbooks had long quoted, and found about as many non-neuronal cells again, not ten times more.

The brain uses roughly what share of the body's energy?

About 20%: the brain makes up only about 2% of body weight, yet it burns a fifth of the body's energy, more than any other organ.

The electrical signals neurons fire are called what?

Action potentials last only a few thousandths of a second in a neuron, and they are not unique to animals: a Venus flytrap snaps shut when touch sets off the same kind of pulse.

Which two groups of animals get by with no neurons at all?

Sponges and placozoans: a sponge filters water without a single nerve cell, yet its genome already holds most of the genes other animals use to wire nerve cells together.

The junction across which one neuron signals to another cell is called what?

A synapse: the word dates from 1897 and comes from the Greek for 'to clasp together', coined while scientists were still arguing over whether nerve cells were separate units at all.

The fatty sheath that insulates axons and speeds up conduction is called what?

Myelin: in multiple sclerosis the immune system strips it from nerve fibres, and signals that once raced along them slow down or fail.

Which glial cells wrap axons in their insulating sheath inside the brain and spinal cord?

Oligodendrocytes: each one wraps stretches of several different axons at once, whereas a Schwann cell, its counterpart in the body's other nerves, wraps just one.

Which part of the brain, only about a tenth of its volume, holds roughly four in five of its neurons?

The cerebellum: its tiny, densely packed granule cells outnumber all the neurons of the far larger cerebral cortex by about four to one.

The memory-forming structure deep in the temporal lobe is named after its resemblance to which animal?

A seahorse: Arantius, the anatomist who first described the curled ridge in 1587, also offered 'white silkworm' as a name, but the fish won.

Which limbic structure, named from the Greek for 'almond', is central to processing fear?

The amygdala: a woman known as S.M., whose amygdalae were destroyed by a rare disease, handled live snakes and toured a haunted house without showing fear.

The thick fibre bundle that links the two cerebral hemispheres is found only in which group of animals?

Placental mammals: kangaroos, koalas and the platypus have no such bundle, and link the two halves of the cortex through an older tract, the anterior commissure, instead.

Broca's area, linked to speech production, sits in which part of the brain?

The frontal lobe: Paul Broca's most famous patient, a man nicknamed Tan who had almost entirely lost the power of speech, was found to have an injury at the back of that lobe.

Which lobe of the cerebrum is dedicated to vision?

Occipital: it sits at the very back of the head, and damage there can leave a person blind even though both eyes still work.

Phineas Gage survived an 1848 accident in which what passed through his head?

A tamping iron: the metre-long rod went in through his left cheek and out through the top of his head; he lived nearly twelve more years, and for a time friends said he was 'no longer Gage'.

Patient H.M. lost the ability to form new memories after 1953 surgery removed most of which brain structure?

The hippocampus: Henry Molaison could still master a tricky mirror-drawing skill over a few days, yet never remembered having practised it.

Which two rivals shared the 1906 Nobel Prize for work on the structure of the nervous system?

Golgi and Ramón y Cajal never agreed: Golgi's own silver stain let Cajal show that nerve cells are separate units, a theory Golgi still rejected when they shared the prize.

Santiago Ramón y Cajal, the doctor who had wanted to be an artist, came from which country?

Spain: his father, an anatomy professor, steered the would-be artist into medicine, and Cajal put his draughtsmanship to work at the microscope.

Hodgkin and Huxley worked out how nerve impulses propagate using which animal's giant axon?

The squid: its giant nerve fibre, about half a millimetre across and nearly a thousand times thicker than ours, was wide enough to take an electrode inside.

Otto Loewi's Nobel-winning proof that nerves signal chemically came to him how?

In a dream: he woke, jotted the idea down and went back to sleep, then found he couldn't read his note; when the dream came back the next night, he went straight to his lab.

Which neurotransmitter do motor neurons release to make muscles contract?

Acetylcholine: in myasthenia gravis the body's own antibodies block the muscles' receptors for it, so muscles tire and weaken quickly with use.

Dopamine is nicknamed the pleasure chemical, but researchers now tie it mainly to what?

Motivation: dopamine marks what is worth wanting and working for; rats drained of almost all their dopamine still showed normal pleasure at a sweet taste.

About 90% of the body's serotonin is made where?

In the gut: cells lining the intestines make it to keep food moving, and because it cannot pass from the blood into the brain, the brain has to make its own small supply.

Botulinum toxin causes flaccid paralysis by blocking the release of a chemical messenger where?

At the neuromuscular junction: a nerve ending that cannot release its messenger leaves the muscle limp, and in tiny injected doses the same effect smooths wrinkles for a few months.

Tetrodotoxin takes its name from the scientific name of which fish?

Pufferfish: the toxin is named after the genus Tetraodon, 'four teeth', and blocks the sodium channels nerves need to fire, which is what makes badly prepared fugu deadly.

The blood-brain barrier is formed mainly by which type of cell?

Endothelial: the cells that make up brain capillary walls are sealed together so tightly that most drugs cannot pass, a standing obstacle to treating brain disease.

Roughly how much cerebrospinal fluid does the human body produce each day?

About 500 mL: only about 150 mL is in circulation at any moment, so the whole supply is replaced roughly four times a day.

The glymphatic system, which flushes waste from the brain, is thought to work hardest during what?

Slow-wave sleep: in sleeping mice the gaps between brain cells widened by about 60%, letting fluid wash through faster, though a 2024 study has challenged the finding.

Mirror neurons were first recorded in the premotor cortex of which animal, by Rizzolatti's team in Parma?

The macaque monkey: the team was recording cells that control grasping when they found that many also fired as the animal merely watched an experimenter pick up food.

Which husband-and-wife team discovered grid cells in the brain in 2005?

Edvard and May-Britt Moser found cells that fire at the corners of a repeating grid of triangles as a rat crosses a room, a built-in coordinate system that won them a 2014 Nobel Prize.

Place cells fire when an animal is in a particular spot; collectively they are thought to form what?

A cognitive map: the phrase comes from Edward Tolman, who argued in 1948 that rats learn the layout of a maze, and place cells, first recorded in 1971, gave the idea a physical basis.

Roughly how many neurons does the roundworm C. elegans, the first animal with a complete wiring diagram, have?

About 300: exactly 302 in the common form of the worm, every one traced through electron-microscope images of serial slices for a map published in 1986.

The light-sensitive proteins that made optogenetics possible were borrowed from which organisms?

Green algae: a single-celled alga uses the protein to steer towards light, and the same channel, placed in a neuron, makes the cell fire whenever light hits it.

Prosopagnosia is the inability to recognise what?

Faces: some people with the condition cannot recognise close family or even their own reflection, and learn to tell people apart by voice or the way they walk.

Split-brain syndrome results from cutting which structure, usually as a last resort for epilepsy?

The corpus callosum: with the link cut, an image shown only to the right half of the brain cannot be named aloud, because that side, as Roger Sperry found, is all but mute.

The cortical homunculus, a distorted 'little man' mapping the body onto the brain, is linked to which neurosurgeon?

Wilder Penfield mapped it in the 1930s by touching an electrode to the exposed brains of awake patients, who told him what they felt; the hands and lips came out huge because so much cortex serves them.

The blue whale is the biggest animal, but which species has the biggest brain ever measured?

The sperm whale: its brain is more than five times the weight of a human's, yet for the size of its body it is modest, one reason brain weight alone is a poor guide to intelligence.

Brain scans of which London workers gave landmark evidence that the adult brain reshapes itself with experience?

Taxi drivers: memorising the city's streets had enlarged part of a brain region used for navigation, and the longer they had driven, the bigger it was; bus drivers on fixed routes showed no such change.

Which part of the brain is a sheet of six layers of neurons?

Neocortex: the sheet is only a few millimetres thick, and in humans it is folded into ridges and grooves so that far more of it fits inside the head.

The output neurons of the cerebellar cortex are named after which scientist?

Purkinje cells, named after a Czech physiologist, are the cerebellar cortex's only way out, and every signal they send is a brake: they inhibit the cells they reach.

António Egas Moniz won the 1949 Nobel Prize in Medicine for which now-notorious brain operation?

The lobotomy: tens of thousands of patients underwent it before chlorpromazine, the first effective drug for schizophrenia, arrived in 1952 and the operation fell from favour.

Functional MRI maps brain activity by tracking changes in what?

Blood oxygen: a busy patch of brain draws in extra oxygen-rich blood, which behaves differently in the scanner's magnetic field, so the image shows where supply has surged, a few seconds late.

Which Greek philosopher held that thought lived in the heart and the brain merely cooled the blood?

Aristotle: in the 4th century BC he made the heart the origin of sensation and movement and the brain a cooling device, overruling earlier Greeks who had put thought in the head.

According to Herodotus, Egyptian embalmers drew the brain out through which part of the body?

The nostrils: by his account the embalmers hooked the brain out with an iron tool and rinsed away the rest, while the heart, regarded as the seat of thought, was left in the body.

Which German anatomist mapped the cerebral cortex into 52 numbered areas in 1909?

Korbinian Brodmann drew his borders purely from how the cells were layered under the microscope, and more than a century on, brain scans are still reported in his numbers.

Eric Kandel won a Nobel Prize for showing how memories form, working mainly with which animal?

A sea slug: Aplysia has just 20,000 or so nerve cells, many of them unusually large, so Kandel could follow a simple reflex and watch single connections strengthen as it learned.

Which disease is caused by the loss of dopamine-producing neurons deep in the brain?

Parkinson's disease: by the time the tremor and stiffness appear, most people have already lost at least half of the dopamine-making cells in a small region called the substantia nigra.

Phrenology, a discredited 19th-century craze, claimed to read a person's character from what?

The shape of the skull: phrenologists felt for bumps they thought were raised by well-developed mental 'organs'; the bumps meant nothing, but the idea that functions sit in particular places survived.

Which US president launched the BRAIN Initiative?

Barack Obama announced it in April 2013 as one of his administration's 'Grand Challenges': a drive, inspired by the Human Genome Project, to build tools that show the brain's circuits at work.

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

Albert Einstein's brain weighed 1,230 grams, and after Harvey cut it into about 240 blocks its sections sat for over twenty years in two mason jars inside a cider box.

Which animal has more than 500 million neurons, with about two-thirds of them inside its arms?

Octopus arms hold about two-thirds of the animal's neurons in their nerve cords, and even a severed arm can still move and respond to stimuli.

Patients can be awake for brain surgery partly because brain tissue has no receptors for which sensation?

Pain cannot be felt by the brain itself, so a headache comes from receptors in the membranes, vessels and muscles of the head and neck instead.

Luigi Galvani discovered 'animal electricity' when sparks made the dead legs of which animals twitch?

Frogs' legs twitching at an electric spark set Galvani on the trail of nerve signals, and Mary Shelley later named galvanism among the ideas behind Frankenstein.

Which toxic metal, used in making felt, gave 19th-century hat makers the tremors of 'mad hatter disease'?

Mercury vapour from the solution used to mat fur into felt left hatters irritable, confused and morbidly shy, a condition doctors call erethism.

Which Austrian neurologist spent four weeks dissecting hundreds of eels before turning to disorders of the mind?

Sigmund Freud was a neurologist before he founded psychoanalysis; as a student in Trieste he cut up eels in an inconclusive search for their male reproductive organs.

The electric jolt of hitting the 'funny bone' at the elbow comes from striking which nerve?

The ulnar nerve is the largest in the human body unprotected by muscle or bone, and 'funny' may be a pun on the humerus, the upper arm bone it runs past.

The stabbing headache nicknamed 'brain freeze' begins when something cold touches which part of the body?

The roof of the mouth is thought to answer cold with a rapid squeeze and swelling of its tiny vessels, and the brain feels the signal as coming from the head.

The parasite Toxoplasma gondii makes infected rats lose their natural aversion to the urine of which predator?

Cats are the only animals in which Toxoplasma can reproduce sexually, which is why scientists suspect the parasite steers its rodent hosts towards them.

The FAST checklist of one-sided drooping, arm weakness and slurred speech helps bystanders spot which emergency?

Stroke patients can be given clot-dissolving drugs only in the first few hours after symptoms begin, which is why FAST, devised in the UK in 1998, ends with time.

The nerve disease ALS is known across America by the name of which Yankees first baseman, diagnosed in 1939?

Lou Gehrig, whose run of 2,130 consecutive games stood as a record for 56 years, had the diagnosis confirmed on his 36th birthday.

Which viral disease, caught from animal bites, travels along nerves to the brain and causes a terror of water?

Rabies sufferers panic at the offer of a drink because swallowing sets off violent throat spasms, and once symptoms appear the disease is virtually always fatal.

Which film star championed spinal cord research after being paralysed from the neck down in a 1995 riding accident?

Christopher Reeve, the star of four Superman films, was thrown from his horse at a competition in Virginia and went on to lead the foundation that carries his name.

The chickenpox virus can lie dormant in nerve cells for decades before reawakening as which blistering rash?

Shingles breaks out when the reawakened virus travels along a nerve to the skin, which is why its blisters form a stripe on one half of the body and stop at the midline.

In which disease, far commoner in women, does the immune system attack the insulation around nerve fibres?

Multiple sclerosis is named for the many scars the attacks leave in the brain and spinal cord, and it becomes much more common the further people live from the equator.

Which sugar, carried around the body in the bloodstream, supplies most of the fuel the brain runs on?

Glucose normally meets most of the brain's needs, though ketones can step in as a major alternative fuel.

Which phenomenon, named by Civil War physician Silas Weir Mitchell, makes most amputees feel a missing arm or leg?

Phantom limb sensations are felt by most amputees, and one much-publicised treatment for the aches they bring is a mirror box.

Which bacterial infection, caught through dirty wounds, makes a toxin that locks the jaw muscles in spasm?

Tetanus toxin silences the nerve cells that normally calm the muscles, setting off spasms that can be strong enough to fracture bones.

Which viral disease, which kills motor neurons in the spinal cord, was the target of Jonas Salk's 1955 vaccine?

Polio paralyses in fewer than one infection in a hundred, when the virus spreads along nerve fibres and destroys the cells that drive the muscles.

Which neurologist wrote The Man Who Mistook His Wife for a Hat and Awakenings, later a Robin Williams film?

Oliver Sacks based Awakenings on his own experience of giving the then-new drug levodopa to post-encephalitic patients at a New York hospital.

Novelist Vladimir Nabokov, who saw every letter of the alphabet in its own colour, had which condition?

Synesthesia ran in Nabokov's family: his mother saw coloured letters too, and his son Dmitri's letter colours were in some cases blends of his parents' hues.

Which nerve, the longest and widest in the human body, runs from the top of the leg down to the foot?

The sciatic nerve divides behind the knee into the tibial and common fibular nerves, and it supplies feeling to the skin of the foot and most of the lower leg.

On the Sacred Disease, an ancient treatise blaming epilepsy on the brain rather than the gods, is attributed to whom?

Hippocrates is the putative author, and the treatise's turn from supernatural to natural causes is counted as a major breakthrough in the history of medicine.

Which B vitamin, now added to grain products in many countries, cuts the risk of spina bifida?

Folic acid fortification of grain products was followed by a fall in US spina bifida births from about 5 to 3.5 in every 10,000.

Naegleria fowleri, which destroys brain tissue after swimmers inhale warm fresh water, is what kind of microbe?

An amoeba by nature, Naegleria fowleri reaches the brain by following the olfactory nerve fibres up from the lining of the nasal cavity.

Auguste D., a woman examined by a German psychiatrist in 1901, was the first recorded case of which illness?

Alzheimer's disease, which Alois Alzheimer went on to describe in 1906, is now the most common cause of dementia, accounting for 60 to 70 per cent of cases.

Which small brain region controls body temperature, hunger and thirst and commands the pituitary gland?

The hypothalamus answers invading microbes by resetting the body's thermostat upward, which is how a fever begins.

Pressure on the median nerve at the wrist, numbing the thumb and first fingers, causes which condition?

Carpal tunnel syndrome often wakes sufferers at night, when wrists tend to stay bent, which is why wearing a wrist splint to bed brings relief.

Which tic disorder, popularly linked with outbursts of swearing, actually involves them in only a minority of cases?

Tourette syndrome is named after the French intern who described nine patients in 1885, and about 1% of school-age children are now thought to have it.

In which disorder can strong emotion make the muscles suddenly go limp, an attack known as cataplexy?

Narcolepsy with cataplexy follows the loss of most of the roughly 70,000 neurons that release orexin, a chemical that helps keep the brain awake.

Which inherited illness, marked by dance-like movements, killed folk singer Woody Guthrie and his mother before him?

Huntington's disease is caused by a dominant mutation, so a single faulty copy of the gene from either parent is enough to bring it on.

A stiff neck and a rash that does not fade under a pressed glass are warning signs of which brain-lining infection?

Meningitis shows its classic trio of stiff neck, sudden high fever and altered mental state in fewer than half of bacterial cases.

Which Scottish city gives its name to the 3-to-15 scale doctors use to rate a patient's level of consciousness?

Glasgow University's Bryan Jennett and Graham Teasdale devised the coma scale, which adds up eye, verbal and motor responses; a 3 means completely unresponsive.

Which branch of the autonomic nervous system widens the pupils and raises goose bumps in fight-or-flight?

Sympathetic nerves arise from near the middle of the spinal cord, and as well as speeding the heart they widen the airways and put the large intestine on hold.

Which lowest part of the brainstem, joining the brain to the spinal cord, controls breathing, heart rate and vomiting?

The medulla oblongata is a cone-shaped mass of neurons, and its involuntary duties run all the way down to sneezing.

Which operation, among the oldest known and practised since Neolithic times, bores a hole through the cranium?

Trepanation left a disc of bone that prehistoric people kept, and it may have been worn as a charm to keep evil spirits away.

A complete wiring diagram of an adult brain, with 139,255 neurons, was published in 2024 for which insect?

Fruit fly brains are small enough to chart cell by cell, a task that becomes daunting in more complex animals with vastly more neurons.

Which land animal has the heaviest brain, holding roughly three times as many neurons as a human brain?

Elephant brains weigh around 5 kg, yet the cerebral cortex, the main seat of cognition, holds only about a third as many neurons as a human's.

Jean-Dominique Bauby dictated The Diving Bell and the Butterfly by blinking his left eyelid, having which condition?

Locked-in syndrome left Bauby's mind intact while paralysing most of his body, so an assistant recited the alphabet until he blinked at the right letter.

Which sense, fed by stretch sensors inside the muscles and tendons, tells the brain where each body part is?

Proprioception can be lost: Ian Waterman, robbed of it from the neck down by a viral infection, could still move but could no longer coordinate his movements.

Which fatal 'laughing sickness' spread among the Fore people of Papua New Guinea through funeral cannibalism?

Kuru takes its name from a Fore word for shaking, and it hit women and children hardest because they usually ate the brain.

Which misfolded proteins, named by Stanley Prusiner, cause mad cow disease by making healthy proteins misfold too?

Prions were named in 1982 by blending the words protein and infection, and they are also blamed for scrapie in sheep and a wasting disease in deer.

Which regularly spaced gaps in a nerve fibre's fatty sheath let electrical signals leap from one gap to the next?

Nodes of Ranvier carry the name of the French anatomist who found them, and the hopping they allow is called saltatory conduction, from the Latin for a leap.

Which doctor to Pergamon's gladiators silenced a squealing pig by tying a nerve, showing the brain controls the voice?

Galen later became personal physician to several Roman emperors, and his views dominated Western medicine for more than thirteen centuries.

Which French psychiatrist gave his name to the delusion that a close relative has been replaced by an impostor?

Joseph Capgras described the delusion in 1923 in a woman who complained that doubles had taken the places of her husband and other people she knew.

Which 17th-century physician coined the word 'neurology' and gave his name to a ring of arteries beneath the brain?

Thomas Willis had distinguished help with his landmark book on the brain: its drawings were supplied by the future architect of St Paul's Cathedral.

Which Caltech scientist won a 1981 Nobel Prize for research on split-brain patients treated for severe epilepsy?

Roger Sperry began with animals, showing that the left and right halves of a divided brain could each learn and remember a different task.

Which German psychiatrist recorded the first human EEG in 1924 while hunting for a physical basis for telepathy?

Hans Berger was set on his path by a close call in army training: his sister, many kilometres away, felt he was in danger and had their father send a telegram.

Which glial cells act as the brain's resident immune defence, scavenging for damaged neurons and infectious agents?

Microglia are not born in the brain at all: they originate in the embryo's yolk sac and travel in to populate it.

Which tissue, found in each of the brain's four ventricles, makes most of the cerebrospinal fluid that bathes the brain?

Choroid plexus tissue makes the fluid by filtering plasma through a layer of specialised cells.