Glossary

Short, plain-language explanations of the technical terms used in the articles and timelines. In an article, hover over a word with a dotted underline (or tap it on a phone) to open its entry in place.

Nuclear fusion (19 terms)

Breeding blanket: The layer surrounding a fusion reactor's plasma. Neutrons striking lithium in it produce tritium fuel, and their energy is captured as heat.
D-T fusion: The fusion of deuterium (D) and tritium (T) into a helium-4 nucleus and a neutron. Almost every fusion reactor now under development is built around this reaction.
Demonstration reactor: The step after an experimental reactor: a machine meant to show that fusion can actually generate electricity. It comes just before a commercial plant.
Deuterium: A heavy form of hydrogen with one proton and one neutron. It is not radioactive and is found in seawater.
H-mode: An operating regime in which turbulence at the plasma edge suddenly dies down and heat confinement roughly doubles. Discovered on Germany's ASDEX tokamak in 1982.
High-temperature superconducting magnet: An electromagnet wound from high-temperature superconductor, a material that loses all electrical resistance at relatively high temperatures. It reaches stronger fields than earlier superconducting magnets.
Ignition: The state in which a plasma keeps burning on the heat of its own fusion products — the helium nuclei — without any outside heating.
Inertial confinement: Crushing a small pellet of fuel with powerful lasers or similar drivers, so that fusion happens in the tiny interval before the fuel flies apart.
ITER: The world's largest tokamak, an experimental fusion reactor being built in southern France by Japan, Europe, the United States, Russia, China, South Korea and India.
Lawson criterion: The condition that a plasma's density, confinement time and temperature must meet for a fusion reactor to produce net energy, derived by John Lawson in Britain in 1955.
Magnetic confinement: Holding a hot plasma away from the vessel walls in a cage of magnetic field, using the fact that charged particles spiral along magnetic field lines.
Neutral beam heating: Heating a plasma by firing in a beam of fast neutral atoms, which hand over their energy in collisions.
Nuclear fusion: A reaction in which light atomic nuclei join to form a heavier one, releasing a large amount of energy. It is what makes the Sun and the stars shine.
Plasma: A gas in which electrons have been stripped from their atoms, so that electrons and nuclei move around separately. Often called the fourth state of matter, after solid, liquid and gas.
Q value: Fusion energy released divided by the energy put in from outside to heat the plasma. Q = 1 is breakeven; Q becoming infinite corresponds to ignition.
Stellarator: A machine that confines plasma using only the magnetic field of intricately twisted coils. Unlike a tokamak, it does not need a large current flowing through the plasma.
Tokamak: A doughnut-shaped machine that confines plasma by combining the magnetic field of external coils with the field produced by a current driven through the plasma itself. The dominant approach to magnetic confinement.
Tritium: A heavy form of hydrogen with one proton and two neutrons. It is weakly radioactive, almost absent in nature, and serves as fusion fuel.
Tritium breeding ratio: The number of new tritium atoms a reactor's blanket makes for each tritium atom burned. Unless it exceeds one, the reactor cannot supply its own fuel.

Quantum computing (13 terms)

Decoding: The calculation that takes the measurements from error correction and works out which qubits suffered which errors.
Entanglement: A state in which two or more qubits or particles cannot be described separately, however far apart they are: they form a single whole.
Fault-tolerant quantum computing: Running quantum computations so that, even though components fail at some rate, layered error correction lets arbitrarily long calculations finish correctly.
Logical error rate: The rate of errors that still remain in a logical qubit after error correction. One of the most important measures of what a quantum computer can really do.
Logical qubit: A single, robust qubit made by bundling many physical qubits together and running error correction on them.
Neutral atom: An approach that uses uncharged atoms as qubits, each one held and positioned by laser light.
Quantum advantage: The point at which a quantum computer solves some computational problem faster than the best classical computer can.
Quantum computer: A computer that calculates using quantum-mechanical properties such as superposition and entanglement. It is expected to solve certain kinds of problem far faster than ordinary computers.
Quantum error correction: Spreading the information of fragile qubits across many of them, so that errors can be detected and fixed.
Quantum LDPC code: A family of error-correcting codes that protect many logical qubits with few physical ones; each check looks at only a handful of qubits.
Qubit: The basic unit of information in a quantum computer. Rather than being either 0 or 1, it can be in a superposition of both.
Superconducting qubit: A qubit made from a superconducting circuit, which has zero electrical resistance at very low temperature. Used by IBM, Google, Fujitsu and others.
Trapped ion: Using atomic ions, suspended in a vacuum by electric fields and manipulated with lasers, as qubits. Used by Quantinuum and others.

Semiconductors (20 terms)

Boolean algebra: Mathematics that represents true and false as 1 and 0 and calculates with AND, OR and NOT much as with addition and multiplication. The foundation of digital circuit design.
CMOS: A circuit style that pairs the two opposite types of MOS transistor. Current flows only at the moment of switching, so power consumption is tiny.
Dennard scaling: The design rule that shrinking a transistor's dimensions and voltage by the same factor makes it faster and more efficient while keeping heat per unit area constant.
DRAM: A memory cell that stores one bit as charge on a capacitor. Simple and cheap to make, it serves as the main memory of computers.
FinFET: A three-dimensional transistor in which the channel stands up like a fish's fin and the gate wraps around it on three sides.
Flip-flop: A circuit that stays in one of two stable states and switches to the other when signalled. The smallest component that can remember one bit.
Gate dielectric: The thin insulating film between the gate electrode and the channel of a MOS transistor. The gate's voltage acts through this film to open and close the channel.
Gate-all-around: A transistor structure in which the channel is a stack of thin sheets (nanosheets), each fully surrounded by the gate on all sides.
Integrated circuit: A circuit in which transistors and other components, together with the wiring between them, are all built into a single piece of semiconductor — a chip.
Moore's law: The rule of thumb that the number of components on a chip keeps doubling at regular intervals. Not a law of physics but a pace the semiconductor industry set itself.
MOS transistor: A transistor built from a metal electrode, an oxide layer and a semiconductor, in which a voltage on the electrode alone opens and closes the channel. Most of today's chips are made of these.
NAND: The logical operation that outputs 0 only when both inputs are 1, and 1 otherwise. Combinations of this one operation are enough to build any logic circuit.
Oxide layer: The thin, glass-like film of silicon dioxide that forms on silicon when it is heated. Impervious to impurities and electrically insulating, it became the foundation of chip manufacturing.
p-n junction: The boundary between n-type semiconductor, rich in electrons, and p-type, rich in holes. It lets current flow in only one direction.
Process node: The name given to a generation of chip-making technology. It is expressed as a length, such as 2 nanometers, but no longer corresponds to any actual dimension.
Stored-program computer: A computer design in which the procedure to be followed, the program, is kept in the same memory as the data. Almost every computer today works this way.
Transistor: A semiconductor device in which a small signal controls a larger current, so it can amplify or switch. The basic component of all electronics.
Turing machine: A very simple imaginary machine that does nothing but read and write symbols on a tape. Alan Turing devised it in 1936 to define what it means for something to be computable.
Vacuum tube: A device that controls a flow of electrons inside an evacuated glass tube. Before the transistor, it did the work of amplifying and switching.
Yield: The fraction of manufactured products that work. In semiconductors, the share of good chips obtained from a wafer.

AI (9 terms)

Feature: In interpretability research, a unit of an AI's internal representation that corresponds to a human-understandable concept, such as the Golden Gate Bridge.
Hallucination: When an AI generates plausible-sounding content that is not grounded in fact or contradicts its source.
Large language model: An AI trained on vast amounts of text that generates language by predicting the next word. The core of ChatGPT, Claude and similar systems.
Mechanistic interpretability: The research field that tries to read an AI's internal computation part by part and explain, as a mechanism, why it produced an answer.
Neural network: A system of simple computing units called neurons, connected in many layers, that learns from data how strong each connection should be and so becomes able to make complex judgements.
Neuron: The smallest unit of computation in a neural network. It weights and sums its inputs and produces an output depending on the result.
Parameter: An adjustable number that determines how a model or a machine behaves. In AI it means the strengths of the connections between neurons, the weights, which are set by training.
Reinforcement learning: Learning better actions by trial and error, guided by a reward given according to the outcome, rather than by being told the right answer.
Sparse autoencoder: An auxiliary neural network used to decompose an AI's internal activity into combinations of a very large number of features, only a few of which are active at once.

Brain–computer interfaces (6 terms)

Biocompatibility: The ability of a material or device placed in the body to keep doing its job without causing harm or rejection.
Brain-computer interface: Technology that reads the brain's electrical signals and turns them into control of a computer or machine. Abbreviated BCI.
Clinical trial: A study in which a new drug or medical device is used in people to establish, step by step, that it is safe and that it works.
Electrode: A conductor that carries electrical signals in or out. In a brain-computer interface it means the fine needles or small contacts that pick up the very weak electricity produced by nerve cells.
Randomized controlled trial: A trial that assigns participants by lot to receive a treatment or not, and compares outcomes, so that the treatment's effect can be measured without bias.
Stentrode: A device that mounts electrodes on a stent — a mesh tube used to hold blood vessels open — and delivers it through the neck to a vein near the brain, reading brain signals through the vessel wall.

Life sciences and medicine (10 terms)

Antibody: A protein that binds to something foreign in the body and marks it for attack. One of the central tools of the immune system.
Antibody-mediated rejection: Rejection in which the recipient produces antibodies against a transplanted organ, and those antibodies attack the organ's blood vessels and gradually impair it.
Blood clotting: The mechanism by which blood solidifies to seal a damaged vessel. A clot that forms inside a blood vessel is called a thrombus.
Carbohydrate antigen: A sugar chain on the cell surface that the immune system uses as a target. In xenotransplantation the key example is α-Gal, present in pigs but absent in humans.
Dialysis: Treatment that uses a machine to remove waste and excess water from the blood in place of kidneys that no longer work.
Genetic modification: Deliberately rewriting the genes of a living thing: switching particular genes off, or adding genes from another species.
Graft survival: A transplanted organ or tissue continuing to work in the recipient without being rejected. How long it lasts is the usual measure of success.
Immunosuppression: Using drugs to weaken the immune system so that it does not reject a transplanted organ.
iPS cell: A body cell, such as a skin cell, given back the ability to become many kinds of cell by introducing a handful of genes.
Xenotransplantation: Transplanting organs or tissues from animals into humans. Today the main candidates are kidneys and hearts from genetically modified pigs.

Robotics (4 terms)

Humanoid robot: A robot with a human-like body — torso, two arms and two legs. Its advantage is being able to use environments and tools built for people.
Learning curve: The fall in cost per unit as more of a product is made. A well-known rule of thumb says cost drops by a fixed proportion each time cumulative output doubles.
Quadruped robot: A robot that walks on four legs. It can move steadily over rough ground and stairs where wheels cannot go.
Self-driving: Technology that lets a car perceive its surroundings with cameras and other sensors and drive itself without a person at the controls.

Batteries and storage (12 terms)

Air electrode: An electrode that uses oxygen from the air in its reaction. It is the positive electrode of metal-air batteries and fuel cells, taking in oxygen on discharge and releasing it on charge.
All-solid-state battery: A lithium-ion battery whose liquid electrolyte is replaced by a solid material. It is expected to be harder to ignite and to store more energy.
Curtailment: Switching off or reducing solar or wind output that could have been generated, because demand or grid capacity is insufficient.
Cycle life: The number of times a battery can be charged and discharged. It is usually counted up to the point where capacity has fallen to 80% of its original value.
Energy density: How much energy a battery stores per unit of weight or volume. The higher it is, the longer a light, small battery lasts.
Grid battery: A large battery connected to the power grid that charges when electricity is plentiful and discharges when it is short.
Iron-air battery: A battery that draws electricity as iron rusts in air and turns the rust back into iron when charged. Its materials are extremely cheap, suiting it to storing energy for days.
Lithium iron phosphate: A type of lithium-ion battery with an iron-phosphate positive electrode. It uses no cobalt or nickel and is cheap, hard to ignite and long-lived.
Lithium-ion battery: A battery that charges and discharges as lithium ions shuttle between the positive and negative electrodes. Used everywhere from phones to electric cars.
Redox reaction: A chemical reaction in which electrons pass from one substance to another. Losing electrons is oxidation, gaining them is reduction, and the two always occur together.
Round-trip efficiency: The share of the electricity put into a battery or other store that can later be taken back out.
Sodium-ion battery: A battery that shuttles sodium ions instead of lithium. Its materials are plentiful and cheap, and it is entering use in grid storage.

Cars and engines (9 terms)

Carnot's theorem: The law that any engine producing work from heat has an efficiency ceiling set only by the temperatures of its hot and cold sides.
Diesel engine: An internal combustion engine that compresses air alone until it is hot, then injects fuel, which ignites by itself. It is more efficient than a spark-ignited petrol engine.
Electric vehicle: A car driven by a motor running on electricity stored in a battery. It emits no exhaust while driving.
Fuel cell: A device that reacts hydrogen with oxygen to produce electricity directly, without combustion. The only exhaust is water.
Hybrid vehicle: A car that carries both an engine and an electric motor and uses each where it works best. It recovers energy into a battery when slowing down, which improves fuel economy.
Internal combustion engine: An engine that burns fuel inside its cylinders and uses the pressure to push pistons. Petrol and diesel engines are both of this kind.
Knocking: Abnormal combustion in an engine in which the fuel-air mixture explodes before the spark ignites it, with a metallic knocking sound.
Tetraethyl lead: A lead compound added to petrol to suppress knocking. It spread lead into the air with the exhaust and was banned worldwide once the harm to health became clear.
Three-way catalyst: A device fitted to the exhaust of a petrol car that turns three kinds of harmful component in the exhaust gas into harmless gases at the same time.

Space (21 terms)

Convex optimization: The class of problems of finding the best answer that have no false answers to get stuck on, so the true best can always be reached quickly.
Geostationary orbit: A circular orbit about 36,000 km above the equator. It matches Earth's rotation, so a satellite there appears fixed in the sky.
Giant-impact hypothesis: The idea that a body about the size of Mars struck the newly formed Earth, and that the debris thrown out gathered to form the Moon.
Gravity assist: Using a planet's gravity and orbital motion to change a spacecraft's speed or direction without fuel as it flies past.
Halo orbit: An orbit that loops widely around a Lagrange point. It is used to keep a spacecraft stationed near the point.
Heliopause: The boundary where the flow of particles from the Sun (the solar wind) is stopped by the gas between the stars — one definition of the outer edge of the solar system.
Hohmann transfer: Moving between two circular orbits by riding an ellipse tangent to both, with just two burns — a fuel-efficient way to transfer.
Ion engine: A thruster that ionises a gas such as xenon and accelerates it electrically to high speed. Its thrust is tiny, but it uses propellant extremely efficiently.
Kepler's laws: Three laws of planetary motion: planets move on ellipses with the Sun at one focus, sweep faster when closer to it, and have orbital periods tied to orbit size.
Kessler syndrome: The prediction that as satellites and fragments multiply in orbit, debris from one collision will trigger more, possibly making the orbit unusable.
Lagrange point: Five points where the gravity of two bodies, such as the Sun and Earth, balances the motion of orbiting around them, so a small object can hold its position.
Liquid-propellant rocket: A rocket that burns liquid fuel and oxidiser fed into a combustion chamber. The burn can be throttled, stopped and restarted.
Multistage rocket: A rocket that sheds the parts whose fuel is spent as it flies. With that weight gone, the remaining stages accelerate faster.
Reusable rocket: A rocket that is recovered after launch, serviced and flown again. Not throwing the vehicle away brings down the cost of launch.
Rocket equation: The equation stating that a rocket's gain in speed depends on its exhaust velocity and on the ratio of its starting mass to its burnt-out mass.
Solar sail: A way of travelling by catching, on a large thin sail, the slight push that sunlight exerts. It uses no fuel.
Solar wind: The stream of charged particles blowing continuously out from the Sun. It fills the solar system at several hundred kilometres per second.
Subsurface ocean: An ocean of liquid water thought to lie beneath the ice shell of an icy moon. A leading candidate for where to look for life.
Three-body problem: The problem of finding how three bodies move under their mutual gravity. Two can be solved with a formula; three in general cannot, and tiny differences can change the future completely.
Universal gravitation: The force by which every object with mass attracts every other. Its strength is proportional to the product of the two masses and inversely proportional to the square of the distance.
Van Allen belt: Doughnut-shaped regions where high-energy protons and electrons are trapped by Earth's magnetic field. There is an inner and an outer belt.

History of physics (43 terms)

Alpha decay: The process in which a heavy atomic nucleus throws out one alpha particle, a helium nucleus, and becomes the nucleus of a different element.
Alpha particle: A heavy, positively charged particle made of two protons and two neutrons: the same thing as a helium nucleus. It is thrown out by radioactive substances.
Atomic nucleus: The tiny, heavy core at the centre of an atom, made of protons and neutrons and carrying a positive charge.
Balmer formula: A simple whole-number formula giving the wavelengths of the visible lines in hydrogen's light, found in 1885 by the Swiss schoolteacher Johann Balmer.
Binding energy: The energy needed to pull something that is held together apart into its pieces. The larger it is, the more tightly the parts are bound.
Blackbody radiation: Light emitted by an ideal body that absorbs all light falling on it. Its spectrum depends only on temperature, not on what the body is made of.
Bohr model: The 1913 model in which electrons circle only on certain orbits and emit light of definite energy when jumping between them.
Boltzmann constant: The fundamental constant, written k, that links temperature to the energy per atom.
Chemical bond: The link that holds atoms together in molecules and crystals, arising from electrons being shared or handed over.
Cloud chamber: A device that makes the path of a charged particle visible as a trail of fine water droplets.
Compton effect: The increase in wavelength of X-rays scattered by electrons. It showed light colliding with electrons as a particle carrying momentum.
Correspondence principle: The principle that quantum results must agree with classical physics in the limit of large quantum numbers — large objects and high energies.
Cosmic ray: High-energy particles raining continuously on Earth from space. Most are protons, coming from the Sun and from far across the galaxy.
Diffraction: The way a wave bends around the edge of an obstacle or spreads out after passing through a narrow gap. Where the waves overlap they reinforce or cancel, producing bright and dark bands.
Dirac equation: The equation describing the electron in a way that satisfies both quantum mechanics and special relativity. Written by Paul Dirac in 1928.
Electron pair: Two electrons grouped together as a pair. When two atoms share an electron pair, a chemical bond forms.
Electronvolt: The unit of energy used for atoms: the energy one electron gains when accelerated through one volt. Its symbol is eV.
Entropy: A quantity measuring how many ways a thing can be spread around. In a system that exchanges nothing with its surroundings, entropy can increase but never decrease.
Equipartition theorem: The classical law that in thermal balance, every way a system can move receives, on average, the same share of energy, proportional to temperature.
Exchange interaction: An effect with no classical counterpart, arising because identical electrons cannot be told apart even when they swap places. It underlies the chemical bond and magnetism.
Fine structure: The splitting of what looks like a single line in an atom's spectrum into several closely spaced lines when examined in detail.
Half-life: The time it takes for the number of radioactive nuclei to fall by half through decay. It is fixed for each kind of nucleus and does not change with temperature or pressure.
Light quantum: The particle-like packet of energy that light behaves as. Now called the photon.
Matrix mechanics: The first form of quantum mechanics, born in 1925: it describes electrons in atoms using only observable quantities, calculated as tables of numbers called matrices.
Matter wave: The idea that things long taken to be particles, such as electrons, also behave as waves. Proposed by Louis de Broglie in 1924.
Neutron: A particle with no electric charge that, together with protons, makes up the atomic nucleus. It weighs almost the same as a proton.
Old quantum theory: The theories of roughly 1900 to 1925, from Planck onwards, that explained phenomena by adding quantum conditions on top of classical physics.
Pauli exclusion principle: The rule that no two electrons in the same atom can be in exactly the same state. Set out by Wolfgang Pauli in 1925.
Periodic table: A table of the elements in order of atomic number, folded so that elements with similar properties line up in columns.
Photoelectric effect: The ejection of electrons from a metal when light shines on it. The energy of each electron depends on the light's frequency (colour), not its intensity.
Planck constant: The fundamental constant, written h, that sets the step size of energy for light and matter. Frequency times h is the smallest unit of energy for that light.
Positron: A particle with the electron's mass and a positive charge. It is the electron's antiparticle; when the two meet, both vanish into light.
Proton: A positively charged particle that, together with neutrons, makes up the atomic nucleus. The nucleus of hydrogen is a single proton. The number of protons decides which element an atom is.
Quantum mechanics: The physical theory describing the behaviour of the very small, such as atoms and electrons. It took shape in 1925–26 and describes the state of a particle in terms of probability.
Quantum tunnelling: The appearance of a particle, with some probability, on the far side of a barrier it lacks the energy to climb over. It happens because particles behave as waves.
Relativity: Einstein's theory that measurements of time and space depend on the observer's motion and on gravity — special relativity (1905) and general relativity (1915–16).
Schrödinger equation: The basic equation of quantum mechanics, which governs how the wave of an electron or other particle varies in space and time. Written down by Erwin Schrödinger in 1926.
Spectrum: Light spread out by wavelength (colour). Atoms and molecules each emit and absorb only certain wavelengths, so thin lines appear in the spectrum.
Spin: A property that electrons and other particles are born with, making them behave like tiny magnets. For an electron it takes only two values: "up" or "down".
Stern–Gerlach experiment: The 1922 experiment showing that a beam of silver atoms passed through a magnetic field splits cleanly in two instead of smearing out: direct evidence that atoms can point only in certain directions.
Ultraviolet catastrophe: The difficulty that classical physics, applied to blackbody radiation, predicts energy growing without limit at short wavelengths.
Uncertainty relation: The quantum relation that a particle's position and momentum cannot both be pinned down as precisely as you like at the same time. Set out by Werner Heisenberg in 1927.
Zeeman effect: The splitting of spectral lines into several when atoms are placed in a magnetic field.

History of psychiatry (34 terms)

Cerebrospinal fluid: The clear fluid that surrounds the brain and spinal cord. A small sample can give clues to diseases of the brain and nerves.
Chlorpromazine: A drug that eases the hallucinations and delusions of schizophrenia. Synthesised in France in 1951 and tried as an aid to anaesthesia, it entered psychiatry in 1952.
Deinstitutionalisation: The movement of patients out of large psychiatric hospitals and back into the community. In the United States, in-patients in state and county mental hospitals fell from about 559,000 in 1955 to about 110,000 in 1985.
Dementia praecox: A diagnosis put together by the German psychiatrist Emil Kraepelin in his 1899 textbook. The name means an early loss of mental powers: an illness that starts young and wears the mind down. It was later renamed schizophrenia.
Dopamine hypothesis: The explanation that in schizophrenia the signal carried by the brain chemical dopamine is too strong. It was built backwards from how effective drugs act, not from the illness itself.
DSM-III: The third edition of the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, published in 1980. It gave each disorder a list of diagnostic criteria, so that different clinicians would be more likely to reach the same diagnosis.
Electroconvulsive therapy: A treatment that passes an electric current through the head to bring on a convulsion. Begun in Rome in 1938 by Ugo Cerletti and colleagues; today it is given under anaesthesia and used for severe depression.
Feighner criteria: Diagnostic criteria for research published in 1972 by psychiatrists at Washington University in St Louis, Missouri. They spelled out which symptoms, how many and for how long, had to be present for a diagnosis, and which cases were excluded.
Fever therapy: A treatment that tried to cure illness by deliberately giving the patient a high fever. Julius Wagner-Jauregg of Vienna began it in 1917 by infecting patients with general paresis with malaria.
General paresis: A disease caused by the syphilis organism entering the brain. Mental symptoms such as memory loss and delusions advance together with bodily ones such as slurred speech and tremor.
Home confinement: Under Japan's Mental Patients' Custody Act of 1900, the system by which families could, with official permission, lock a person with mental illness in a room at home. It was prohibited by the Mental Hygiene Act of 1950.
Hypnosis: Leading a person by suggestion into a special, sleep-like state of consciousness. Physicians used it for treatment and research at the end of the nineteenth century.
Hysteria: In nineteenth-century medicine, the name for an illness in which symptoms such as paralysis or fits appear although no injury or lesion can be found to explain them.
Imipramine: Regarded as the first antidepressant. It failed as a candidate drug for schizophrenia, and in 1957 the Swiss psychiatrist Roland Kuhn reported its effect on depression.
Insulin coma therapy: A treatment for schizophrenia in which large doses of insulin put the patient into a coma. Reported by Manfred Sakel in 1933 and widely adopted, but a controlled trial in 1957 found no effect of the insulin itself.
Kappa: A measure of how far two raters agree, after removing the agreement expected by chance: 1 means perfect agreement and 0 means no better than chance. It was used to measure how often psychiatrists agree on a diagnosis.
Lithium carbonate: A lithium drug used to prevent relapses of mania and depression. In 1949 the Australian psychiatrist John Cade reported its effect on mania after experiments on guinea pigs.
Lobotomy: An operation that cuts the connections between the frontal lobes and the rest of the brain. Begun by Egas Moniz of Portugal in 1935 as "leucotomy", it spread in the United States under the name "lobotomy".
Manic-depressive insanity: An illness in which periods of elevated mood and overactivity alternate with periods of depression. Kraepelin put it together in 1899, set apart from dementia praecox.
Mental Health Act: A Japanese law of 1987 that revised and renamed the Mental Hygiene Act. It introduced admission based on the patient's own consent (voluntary admission) and Psychiatric Review Boards.
Mental Hygiene Act: A Japanese law of 1950 that prohibited home confinement and required patients to be cared for in hospitals and other designated facilities. Revised in 1987, it became the Mental Health Act.
Mental Patients' Custody Act: Japan's first law on people with mental illness, passed in 1900. It placed the duty of looking after patients on their families and allowed them to confine patients with official permission.
Moral treatment: An approach from the late eighteenth and nineteenth centuries that tried to cure mental illness by listening and by working on feelings and thoughts, not by drugs or bodily procedures. "Moral" here does not mean a lesson in right and wrong.
Neurosis: A diagnostic grouping used until the mid-twentieth century for states of anxiety, compulsion, hysteria and the like.
Placebo: A tablet or similar that looks like the real drug but contains no active ingredient. Comparing a drug against it shows whether the drug really works.
Psychiatric Review Board: A body set up in each Japanese prefecture by the Mental Health Act of 1987, to which people admitted to psychiatric hospital against their will can apply for discharge or better treatment.
Psychoanalysis: The method of treatment created by Sigmund Freud, which looks for the causes of symptoms in what the patient says, together with the theory built on it.
Remission: A state in which the symptoms of an illness have subsided. In Rosenhan's 1973 paper, the pseudopatients were said to have been discharged with a diagnosis of schizophrenia in remission.
Research Diagnostic Criteria: Diagnostic criteria for research in psychiatry, built by Spitzer and colleagues on the Feighner criteria. They became central to DSM-III in 1980.
Schizophrenia: An illness in which the connections between mental functions such as thought and feeling break down. The word was coined in 1908 by the Swiss psychiatrist Eugen Bleuler.
Straitjacket: A garment with long sleeves that fasten the arms against the body, used to restrain a violent person. At the end of the eighteenth century it began to replace iron chains.
Syphilis: An infection caused by a spiral-shaped bacterium, Treponema pallidum. It spreads mainly by sex and, after many years, can attack the brain and nerves.
Talking cure: A treatment that tries to relieve symptoms by having the patient talk. The name was given in English in the early 1880s by Josef Breuer's patient known as Anna O.
Voluntary admission: Admission to a psychiatric hospital on the basis of the patient's own consent. In Japan it first entered the law with the Mental Health Act of 1987.

History of genetics (5 terms)

Apomixis: The setting of seed without fertilisation. The seed inherits as its mother did, so even a hybrid's offspring do not split. It occurs in the hawkweeds Mendel turned to after his peas.
Dominant and recessive: In a hybrid, the form of a trait that shows is called dominant and the one that stays hidden is called recessive. The terms are Mendel's own: dominirend and recessiv.
Gene: Whatever is passed from parent to offspring and settles a hereditary trait. When Wilhelm Johannsen coined the word Gen in 1909, it was a name with nothing known behind it.
Law of segregation: The rule that the two differing hereditary elements in a hybrid separate when egg cells and pollen are formed, so that each receives one or the other. Mendel set it out in 1866; it was rediscovered in 1900.
Self-pollination: The pollination of a flower by its own pollen. Peas pollinate themselves before the flower opens, so stray pollen rarely gets in and a cross made by hand stays the cross intended.

History of consciousness science (15 terms)

Alpha wave: An EEG rhythm of about ten waves a second, strongest at the back of the head when a person rests with the eyes shut. Berger named it in 1929 and reported that it vanishes when the eyes open.
Behaviorism: The position that psychology should be built as a natural science whose aim is to predict and control observable behavior. John Watson set it out in 1913 in Psychology as the Behaviorist Views It.
Corpus callosum: The thick bundle of nerve fibers that joins the right and left halves of the cerebrum. Surgeons began cutting it in 1940 to treat epilepsy, and in the 1960s researchers began testing the two halves of such patients separately.
Electro-oculogram: A record of the electrical changes in the skin around the eye as it moves. The eyeball carries a small voltage between front and back, so its movements can be picked up by electrodes.
Electroencephalogram: A recording of the brain's electrical fluctuations, usually through electrodes on the head. The German psychiatrist Hans Berger reported human recordings in 1929 and named them the Elektrenkephalogramm.
Imageless thought: The claim that thoughts as such, made of neither words nor images, are present in consciousness. Psychologists at Würzburg in Germany put it forward in the early 1900s, and it set off a long dispute.
Introspection: Observing and reporting what is going on in one's own mind. It was one of the methods of early psychology, but researchers differed widely on how far it could be trusted.
Left-brain interpreter: The work of the left hemisphere that explains one's own actions and ties them into a single story. Michael Gazzaniga and Joseph LeDoux named it from observations of split-brain patients. It supplies a sensible reason even when it does not know the real one.
Optic chiasm: The place at the base of the brain where some of the fibers from each eye cross to the other side. In split-brain animal studies it was cut down the middle, so that what one eye saw reached only the hemisphere on the same side.
Psychophysics: The study, in numbers, of how the strength of a stimulus relates to the strength of the sensation it produces. Gustav Fechner founded it in his Elemente der Psychophysik of 1860.
REM sleep: Periods of sleep in which both eyes move together in rapid jerks. Eugene Aserinsky and Nathaniel Kleitman reported them in 1953; sleepers woken during them usually described detailed dreams.
Reticular formation: The core of the brainstem, where nerve cells and fibers interlace like a net. In 1949 Giuseppe Moruzzi and Horace Magoun reported that stimulating it turns the EEG into the pattern of waking.
Split brain: A brain whose corpus callosum and other connections between the halves have been cut, so that the right and left halves work separately. Animal studies in the 1950s and patient studies from 1962 showed that what one half saw or learned, the other did not know.
Subtraction method: Comparing reaction times for tasks that differ by one added step, and taking the difference as the time that step takes in the mind. The Dutch physiologist Franciscus Donders published it in 1868.
Threshold: The strength below which a stimulus is not felt at all. Fechner called sensations above the threshold conscious, and gave those below it negative values as unconscious sensations.