An isolated brain is a brain kept alive in vitro, either by perfusion by a blood substitute, often an oxygenated solution of various salts, or by submerging the brain in oxygenated artificial cerebrospinal fluid (CSF). It is the biological counterpart of brain in a vat. A related concept, attaching the brain or head to the circulatory system of another organism, is called a head transplant. An isolated brain however is more typically attached to an artificial perfusion device rather than a biological body.
The brains of many different organisms have been kept alive in-vitro for hours, or in some cases days. The central nervous system of invertebrate animals is often easily maintained as they need less oxygen and to a larger extent get their oxygen from CSF; for this reason their brains are more easily maintained without perfusion. Mammalian brains on the other hand have a much lesser degree of survival without perfusion and an artificial blood perfusate is usually used.
For methodological reasons, most research on isolated mammalian brains has been done with guinea pigs. These animals have a significantly larger basilar artery (a major artery of the brain) compared to rats and mice, which makes cannulation (to supply CSF) much easier.
- 1812 – Julien Jean César Le Gallois (a.k.a. Legallois) put forth the original idea for resuscitating severed heads through the use of blood transfusion.
- 1818 – Mary Shelley published Frankenstein; or, the Modern Prometheus.
- 1836 – Astley Cooper showed in rabbits that compression of the carotid and vertebral arteries leads to death of an animal; such deaths can be prevented if the circulation of oxygenated blood to the brain is rapidly restored.
- 1857 – Charles Brown-Sequard decapitated a dog, waited ten minutes, attached four rubber tubes to the arterial trunks of the head, and injected blood containing oxygen by means of a syringe. Two or three minutes later voluntary movements of the eyes and muscles of the muzzle resumed. After cessation of oxygenated blood transfusion movements stopped.
- 1887 – Jean Baptiste Vincent Laborde made what appears to be first recorded attempt to revive the heads of executed criminals by connecting the carotid artery of the severed human head to the carotid artery of a large dog. According to Laborde's account, in isolated experiments a partial restoration of brain function was attained.
- 1912 – Corneille Heymans maintained life in an isolated dog's head by connecting the carotid artery and jugular vein of the severed head to the carotid artery and jugular vein of another dog. Partial functioning in the severed head was maintained for a few hours.
- 1928 – Sergey Bryukhonenko showed life could be maintained in the severed head of a dog by connecting the carotid artery and jugular vein to an artificial circulation machine.
- 1963 – Robert J. White isolated the brain from one monkey and attached it to the circulatory system of another animal.
In philosophy, the brain in a vat is any of a variety of thought experiments intended to draw out certain features of our ideas about knowledge, reality, truth, mind, and meaning. A contemporary version of the argument originally given by Descartes in Meditations on First Philosophy (i.e., that he could not trust his perceptions on the grounds that an evil demon might, conceivably, be controlling his every experience), the brain in a vat is the idea that a brain can be fooled into anything when fed appropriate stimuli.
The inherently philosophical idea has also become a staple of many science fiction stories, with many such stories involving a mad scientist who might remove a person's brain from the body, suspend it in a vat of life-sustaining liquid, and connect its neurons by wires to a supercomputer which would provide it with electrical impulses identical to those the brain normally receives. According to such science fiction stories, the computer would then be simulating a virtual reality (including appropriate responses to the brain's own output) and the person with the "disembodied" brain would continue to have perfectly normal conscious experiences without these being related to objects or events in the real world.
Growing an isolated brain
Isolated biological "brains", grown from cultured neurons which were originally separated, have been developed. These are not the same thing as the brains of organisms, but they have been used to control some simple robotic systems.
Teams at the Georgia Institute of Technology and the University of Reading have created neurological entities integrated with a robot body. The brain receives input from sensors on the robot body and the resultant output from the brain provides the robot's only motor signals.
Isolated brains in fiction
The concept of a brain in a jar (or brain in a vat) is a common theme in science fiction:
- The final novel in C.S. Lewis's "Space Trilogy," That Hideous Strength, uses the isolated brain of Francois Alcasan, an Algerian radiologist guillotined for murder, as a plot device. At some point in the novel, it is revealed that Alcasan's artificially-perfused head is used to allow evil intelligence to communicate with humans directly.
- Many people in the Ghost in the Shell manga and anime franchise possess cyberbrains, which can sustain a modified human brain within a cybernetic body indefinitely.
- In the Fallout series of games, isolated brains are used to control robots.
- In the Captain Future anime, the character "Prof. Simon Wright" is a human brain living in a transparent case 
- The Mi-go aliens in the Cthulhu Mythos of H. P. Lovecraft, first appearing in the story "The Whisperer in Darkness" (1931), can transport humans from Earth to Pluto (and beyond) and back again by removing the subject's brain and placing it into a "brain cylinder", which can be attached to external devices to allow it to see, hear, and speak.
- In Alexander Beliaev's novel Head of Prof. Dowell (1925), Professor Dowell discovers a way of keeping heads of dead people alive and even to give them new bodies. After his death Dowell himself becomes a subject of such an experiment
- In Donovan's Brain (see term), the 1942 science fiction novel by Curt Siodmak (filmed three times in different versions: 1942, 1953 and 1962), the brain of a ruthless millionaire is kept alive in a tank where it grows to monstrous proportions and powers.
- In Roald Dahl's short story "William and Mary" (1960), after William's death his brain is kept alive on an artificial heart.
- The Ruinators, later known as the Demiurges, are the immensely cyborgized alien society in the Humans as Gods, the 1966–1977 sci-fi trilogy by Sergey Snegov. They use the isolated brains of the highly intelligent species Galaxians as the organic supercomputers in charge of the Metrics Stations, the primary and most secret military defense structure of the Ruinators' Empire. The brains are being extracted from the prisoners' babies and grown artificially in the spheres filled with the nutrient liquid. Among the most important characters of the 2nd and 3d novels comes the Brain of the Third Planet, later known as Vagrant or Voice, who has somehow developed self-consciousness and later rebelled against the Ruinators. Due to the Vagrant's fervent desire for a life of those embodied, the Brain has been surgically put into the dragon body, whose inherent brain was destroyed in the recent battle. Vagrant enjoyed a sentient dragon's life for a few decades after that, until the body grew too senile, and on the threshold of the dragon's death the brain was removed again to assume control over a starship.
- In the 1970s Doctor Who serial The Brain of Morbius, Solon, an authority on micro-surgical techniques, transplants Morbius's brain into an artificial translucent brain cylinder casing. Additionally, in the modern Doctor Who series (2005–present), the recurring antagonists known as the Cybermen are presented as human brains (in one instance, an entire human head) encased in mechanical exoskeletons, connected by an artificial nervous system; this is ostensibly done as an "upgrade" from the comparatively fragile human body to a far more durable and longer-lasting shell. Another group of modern Who foes, the Toclafane, were revealed to be human heads encased in flying, weaponized spheres, the final forms of humans from the far future who turned to desperate measures in order to survive the conditions of the impending heat death of the universe.
- In the Legends of Dune prequel trilogy to the novel Dune, Cymeks are disembodied brains that wear robotic bodies.
- The mad scientist in the French movie The City of Lost Children has a "brain in a vat" for a companion.
- In RoboCop 2, the brain, eyes, and much of the nervous system of the Detroit drug lord Cain is harvested by OCP officials to use in their plans for an upgraded "RoboCop 2" cyborg. These systems are stored in a vat shortly after the surgery, where the disembodied Cain can still see the remains of his former body being discarded before being placed into the fitted robotic skeleton.
- The B'omarr Monks, of the Star Wars Universe, would surgically remove their brains from their bodies and continue their existence as a brain in a jar. They believe that cutting themselves off from civilization and all corporeal distractions leads to enlightenment. These monks are easily identified in Return of the Jedi as the spider like creature that walks past C-3PO as he enters Jabba’s Palace.
- In the animated series Futurama, numerous technological advances have been made by the 31st century. The ability to keep heads alive in jars was invented by Ron Popeil (who has a guest cameo in "A Big Piece of Garbage") and also apparently Dick Clark of Dick Clark’s New Year’s Rockin’ Eve fame still doing the countdown in the year 2999, has resulted in many political figures and celebrities being active; this became the writers' excuse to feature and poke fun at celebrities in the show.
- A brainship is a fictional concept of an interstellar starship. A brainship is made by inserting the disembodied brain and nervous system or malformed body of a human being into a life-support system, and connecting it surgically to a series of computers via delicate synaptic connections (a Brain–computer interface.) The brain "feels" the ship (or any other connected peripherals) as part of its own body. An example, The Ship Who Sang (1969) short story collection by science fiction author Anne McCaffrey is about the brainship Helva.
- The video game Cortex Command revolves around the idea of brains being separated from physical bodies, and used to control units on a battlefield.
- The science fantasy television series LEXX includes a robot head containing human brain tissue. Also whenever the current Divine Shadow body dies his brain is removed and placed in a device that allows him to speak and kept with rest of the Divine Predecessors.
- In the Doctor Who episodes "The End of the World" and "New Earth," Lady Cassandra is an isolated brain attached to a canvas of skin with a face.
- In the movie Blood Diner, two cannibal brothers bring their uncle's (isolated) brain back to life to help them in their quest to restore life to the five-million-year-old goddess Shitaar. Their uncle's brain instructs them to collect the required parts to resurrecting Shitaar – virgins, assorted body parts from whores, and the ingredients for a "blood buffet".
- In the science fiction comedy film The Man with Two Brains, the protagonist, a pioneering neurosurgeon, falls in love with a disembodied brain that was able to communicate with him telepathically.
- The Outer Limits episode "The Brain of Colonel Barham" details the story of a dying astronaut, Colonel Barham. It is decided to separate his brain from his body and keep it alive, with neural implants connecting it to visual and audio input/output for the mission. But without a body, the brain becomes extremely powerful and megalomaniacal.
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