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A positronic brain is a fictional technological device, originally conceived by science fiction writer Isaac Asimov. Its role is to serve as a central computer for a robot, and, in some unspecified way, to provide it with a form of consciousness recognizable to humans. When Asimov wrote his first robot stories in 1939/1940, the positron was a newly discovered particle and so the buzz word positronic, coined by analogy with electronic, added a contemporary gloss of popular science to the concept.
Asimov remained vague about the technical details except to assert that the brain's substructure was formed from an alloy of platinum and iridium. It was stated to be very vulnerable to radiation, and apparently a type of volatile memory (since robots in storage required a power source keeping their brains "alive"). The focus of Asimov's stories was directed more towards the software of robots (such as the Three Laws of Robotics) than the hardware in which it was implemented, although it is stated in his stories that to create a positronic brain without the Three Laws it would have been necessary to spend years redesigning the brain itself.
A positronic brain cannot ordinarily be built without incorporating the Three Laws; any modification thereof would drastically modify robot behavior. Behavioral dilemmas resulting from conflicting potentials set by inexperienced and/or malicious users of the robot for the Three Laws make up the bulk of Asimov's stories concerning robots. They are resolved by applying the science of logic and psychology together with mathematics, the supreme solution finder being Dr. Susan Calvin, Chief Robopsychologist of U.S. Robots.
The Three Laws are also a bottleneck in terms of brain sophistication. Very complex brains designed to handle world economy interpret the First Law in expanded sense to include humanity as opposed to a single human; in Asimov's later works like Robots and Empire this is referred to as the "Zeroth Law". At least one brain constructed as a calculating machine as opposed to being a robot control circuit was designed to have a flexible, childlike personality so that it was able to pursue difficult problems without the Three Laws inhibiting it completely. Specialized brains created for overseeing world economics were stated to have no personality at all.
Under specific conditions, the Three Laws can be obviated, with the modification of the actual robotic design.
- Robots which are of low enough value can have the Third Law deleted; they do not have to protect themselves from harm, and the brain size can be reduced by half.
- Robots that do not require orders from a human being may have the Second Law deleted, and therefore require smaller brains again, providing they do not require the Third Law.
- Robots that are disposable, cannot receive orders from a human being and are not able to harm a human, will not require even the First Law. The sophistication of positronic circuitry renders a brain so small that it could comfortably fit within the skull of an insect.
Robots of the aforementioned last type directly parallel contemporary industrial robotics practice, though real-life robots do contain safety sensors and systems, in a concern for human safety (a weak form of the First Law; the robot is a safe tool to use, but has no "judgment", which is implicit in Asimov's own stories).
Several robot stories have been written by other authors following Asimov's death. For example, in Roger MacBride Allen's Caliban trilogy, a Spacer roboticist called Gubber Anshaw invents the gravitonic brain. It offers speed and capacity improvements over traditional positronic designs, but the strong influence of tradition make robotics labs reject Anshaw's work. Only one roboticist, Fredda Leving, chooses to adopt gravitonics, because it offers her a blank slate on which she could explore alternatives to the Three Laws. Because they are not dependent upon centuries of earlier research, gravitonic brains can be programmed with the standard Laws, variations of the Laws, or even empty pathways which specify no Laws at all.
Appearances in science fiction 
The Avengers 
In a mini story entitled "Night Vision!" in Annual #6 of the Marvel comic, writer Scot Edelman refers to the brain of the synthezoid "The Vision" as positronic. The Vision had a complicated history, being born of the dead android body of the original Human Torch, and the mind of the dead human Wonder Man, not to mention being programmed to be a killing machine by the armageddon-happy sentient robot Ultron, who in his turn had been inadvertently created by scientist Henry Pym, originally as a lab assistant. He overcame his programming and became a hero, but The Vision was always alternately coldly logical and given to violent emotion, and was very able to break all three laws.
Doctor Who 
In the fourth season (1966–67) Doctor Who story "The Power of the Daleks", second incarnation of the Doctor, played by Patrick Troughton, awakens from his first regeneration and eventually faces one of his old nemeses, the Daleks, a race of armed robotic tank shells with organic operators. Human space colonists examine "dead" Daleks and, upon their re-activation, conjecture as to "what sort of positronic brain must this device possess." However, the Daleks are actually organic life-forms that were encased in robotic shells, and thus do not possess the purported positronic brain and, in any case, do not obey the Three Laws of Robotics.
Also in the fourth season, in "The Evil of the Daleks" the Doctor is forced to work for the Daleks in extracting the "human factor" from Jamie's emotions, which he imprints into a positronic brain. This is to be implanted in the Daleks, which the Daleks hope will make them invincible.
In the seventeenth season (1979–80) story "The Horns of Nimon", the fourth incarnation of the Doctor, played by Tom Baker, recognizes the Labyrinth-like building complex that serves as the lair of the Nimons as resembling both physically and functionally a "giant positronic circuit". When adequately fuelled, the giant circuit was capable of transferring massive amounts of energy over vast distances in order to generate two black holes as gateways to hyperspace and to sustain a tunnel that served as the motive power between them for the transport of an invading force of Nimons from the dying planet Crinoth to Skonnos.
In the fifth series (2010) Doctor Who story "Victory of the Daleks", the Daleks creates a human-cyborg scientist 'Bracewell', that is implanted in to the British scientific community to develop technology for the war effort. The creation was said to be controlled by a positronic brain.
Blade Runner 
Star Trek 
Several fictional characters from the "Star Trek" series "The Next Generation"—Lieutenant Commander Data, his "mother" Julianna Soong Tainer, and his brothers Lore and B-4—are androids equipped with positronic brains created by Dr. Noonien Soong. Data explains in “Time's Arrow, Part 1” that Lore’s positronic brain is equipped with a type L phase discriminating amplifier and Data's own with a type R. In the episode "The Offspring", Data creates an offspring named Lal with a similar but somewhat more sophisticated brain. After a short time she displays promising advances in emotion and other human behaviors that Data has not been able to master, but later dies of a "rapid positronic cascade failure" shortly after she is told that Starfleet wants to separate her from Data. In the episode Datalore, Lieutenant Natasha Yar refers to the positronic brain as Asimov's dream (although in reality, Asimov admitted that he was only looking for a "scientific" sounding word when choosing the term "positronic"). Because Lore was malevolent, and Data was an independent entity, it is unlikely that Tasha was referring only to the Laws of Robotics. The episode "Brothers" depicts an unnumbered quantity of androids (and/or android parts) that preceded both Lore and Data. These are assumed to also possess positronic brains in some form or fashion with each being an improvement over the last.
None of these androids are constrained by Asimov's robot laws; Lore, lacking ethics and morals, kills indiscriminately. Data, though his actions are restricted by ethical programming provided by his creator, is also capable of killing in situations where it is absolutely necessary.
"Positronic implants" were used to replace lost function in Vedek Bareil's brain in the Deep Space 9 episode "Life Support".
Once Upon a Time... Space 
The animated sci-fi series Once Upon a Time... Space features an android with a positronic brain, Métro.
Perry Rhodan 
In the German science fiction series Perry Rhodan, positronic brains (German: Positroniken) are the main computer technology; for quite a time they are replaced by the more powerful Syntronics, but those stop working due to the increased Hyperimpedance. The most powerful positronic brain is called NATHAN and covers large parts of the Earth's moon. Many of the larger computers (including NATHAN) as well as the race of Posbis combine a biological component with the positronic brain, giving them sentience and creativity.
I, Robot, 2004 Film 
The robots in the 2004 film I, Robot (loosely based on one of Isaac Asimov's stories) also have positronic brains. Sonny, one of the main characters from the film, has two separate positronic brains—the second being a positronic "heart"—so it has choices open to him the other robots in the film do not have. Sonny also has the possibility of being able to develop emotions and a sense of right and wrong independent of the Three Laws of Robotics; it has the ability to choose not to obey them.
The film also features a colossal positronic brain, VIKI, who is bound by the Three Laws. Its interpretation of the laws allows VIKI to directly harm humans in order to protect humanity as a whole in an application of the Zeroth Law.
Bicentennial Man 
The robots in the 1999 film Bicentennial Man (based on one of Asimov's stories) also have positronic brains, including the main character Andrew, an NDR series robot that starts to experience human characteristics such as creativity. Only when Andrew allows his positronic brain to "decay", thereby willfully abandoning his immortality, is he declared a human being. This event takes place on the two-hundredth anniversary of his creation, hence the title.
The Number of the Beast 
In The Number of the Beast by Robert A. Heinlein published in 1980, positronic brains are mentioned fleetingly in chapter 46 as a threatened replacement for Dora, a space yacht's computer from various others of Heinlein's books, including The Cat Who Walks Through Walls.
Tiny Tank 
The titular protagonist of the PlayStation game Tiny Tank has a positronic brain, which is revealed during one of the many comical arguments he has with the director of an ad campaign designed to prove his superiority to humans at serving his wartime functions.