Trepanation
Trepanation (also known as trepanning, trephination, trephining or burr hole) is surgery in which a hole is drilled or scraped into the skull, thus exposing the dura mater in order to treat health problems related to intracranial diseases, though in the modern era it is used only to treat epidural and subdural hematomas, as an extreme body modification, and for surgical access for certain other neurosurgical procedures, such as intracranial pressure monitoring.
Trepanation was carried out for both medical reasons and mystical practices for a long time:
evidence of trepanation has been found in prehistoric human remains from Neolithic times onwards, per cave paintings indicating that people believed the practice would cure epileptic seizures, migraines, and mental disorders.  Furthermore, Hippocrates gave specific directions on the procedure from its evolution through the Greek age.
The modern medical procedure of corneal transplant surgery uses a technique known as trepanning or trephining, however the operation is conducted on the eye (not the skull), with an instrument called a trephine.

# History of trepanation

## Trepanation in the Old World
See also Prehistoric Medicine
Trepanation is perhaps the oldest surgical procedure for which there is evidence, and in some areas may have been quite widespread. Out of 120 prehistoric skulls found at one burial site in France dated to 6500 BC, 40 had trepanation holes. Surprisingly, many prehistoric and premodern patients had signs of their skull structure healing; suggesting that many of those that proceeded with the surgery survived their operation.
Trepanation was also practiced in the classical and Renaissance periods. Hippocrates gave specific directions on the procedure from its evolution through the Greek age, and Galen elaborates on the procedure, too.  Doctors in ancient Egypt used the scrapings of the skull to create love potions and other concoctions.
During the Middle Ages and the Renaissance, trepanation was practiced as a cure for various ailments, including seizures and skull fractures. The surgeons who performed these trepanations were probably highly skilled because the survival rate of the operations was high and the infection rate was low.

## Trepanation in pre-Columbian Mesoamerica
In pre-Columbian Mesoamerica, evidence for the practice of trepanation and an assortment of other cranial deformation techniques comes from a variety of sources, including physical cranial remains of pre-Columbian burials, allusions in iconographic artworks and reports from the post-colonial period.
Among New World societies, trephinning is most commonly found in the Andean civilizations such as the Inca. Its prevalence among Mesoamerican civilizations is much lower, at least judging from the comparatively few trepanated crania which have been uncovered.
The archaeological record in Mesoamerica is further complicated by the practice of skull mutilation and modification which was carried out after the death of the subject, in order to fashion "trophy skulls" and the like of captives and enemies.  This was a reasonably widespread tradition, illustrated in pre-Columbian art which on occasion depicts rulers adorned with or carrying the modified skulls of their defeated enemies, or of the ritualistic display of sacrificial victims. Several Mesoamerican cultures used a skull-rack (known by its Nahuatl term, tzompantli ) on which skulls were impaled in rows or columns of wooden stakes.
Even so, some evidence of genuine trepanation in Mesoamerica (i.e., where the subject was living) has been recovered.
The earliest archaeological survey published of trepanated crania was a late 19th-century study of several specimens recovered from the Tarahumara mountains by the Norwegian ethnographer Carl Lumholtz. Later studies documented cases identified from a range of sites in Oaxaca and central Mexico, such as Tilantongo, Oaxaca and the major Zapotec site of Monte Alban. Two specimens from the Tlatilco civilization's homelands (which flourished around 1400 BCE) indicate the practice has a lengthy tradition.
A study of ten low-status burials from the Late Classic period at Monte Alban concluded that the trepanation had been applied non-therapeutically, and, since multiple techniques had been used and since some people had received more than one trepanation, concluded it had been done experimentally. Inferring the events to represent experiments on people until they died, the study interpreted that use of trepanation as an indicator of the stressful sociopolitical climate that not long thereafter resulted in the abandonment of Monte Alban as the primary regional administrative center in the Oaxacan highlands.
Specimens identified from the Maya civilization region of southern Mexico, Guatemala and the Yucatan Peninsula show no evidence of the drilling or cutting techniques found in central and highland Mexico. Instead, the pre-Columbian Maya seemed to have utilised an abrasive technique which ground away at the back of the skull, thinning the bone and sometimes perforating it, similar to the examples from Cholula. Many of the skulls from the Maya region date from the Postclassic period (ca. 9501400), and include specimens found at Palenque in Chiapas, and recovered from the Sacred Cenote at the prominent Postclassic site of Chichen Itza in northern Yucatan.

# Trepanation in modern medicine
Trepanation is a widely accepted treatment for epidural and subdural hematomas, and for surgical access for certain other neurosurgical procedures, such as intracranial pressure monitoring.  Modern surgeons generally use the term craniotomy for this procedure.  In almost all cases, the removed piece of skull is replaced as soon as possible.  If the bone is not replaced, then the procedure is considered a craniectomy.

# Voluntary trepanation
Although considered today to be pseudoscience, the practice of trepanation for other purported medical benefits continues.  The most prominent explanation for these benefits is offered by Bart Huges (also known as Hughes), sometimes referred to as "Dr. Bart Hughes" even though he did not complete his medical degree.  Hughes claims that trepanation increases "brain blood volume" and thereby enhances cerebral metabolism in a manner similar to cerebral vasodilators such as gingko biloba.  No published results of clinical trials of trepanation have supported these claims.  There is an ongoing study involving pre and post operative MRI in a Mexican cosmetic surgery clinic.  Publication of this study is uncertain.
Other modern practitioners of trepanation claim that it holds other medical benefits, such as a treatment for depression or other psychological ailments. In 2000 two men from Cedar City, Utah were prosecuted for practicing medicine without a license after they performed a trepanation on an English woman to treat her chronic fatigue syndrome and depression.
However, most individuals who practice non-emergency trepanation today do so for psychic purposes. A prominent proponent of the modern view is Peter Halvorson, who drilled a hole in the front of his own skull to increase "brain blood volume".  Amanda Feilding performed a self-trepanation with a drill, while her partner Joey Mellen filmed the operation, in the film titled Heartbeat in the Brain.  The film has since been lost.
In a chapter of his book, Eccentric Lives & Peculiar Notions, John Michell describes a British group that advocates self-trepanation, that is, the drilling of a hole in the skull to allow the brain access to more space and oxygen.  The chapter is called "The People With Holes in their Heads".
According to Michell, the Dutchman Bart Huges (sometimes written as "Bart Hughes") pioneered the idea of trepanation.  Huges' 1962 monograph, Homo Sapiens Correctus, is cited by most advocates of self-trepanation.  Among other arguments, he contends that since children have a higher state of consciousness, and children's skulls are not fully closed, that one can return to an earlier, childlike state of consciousness by self-trepanation.  Further, by allowing the brain to freely pulsate, Huges argues that a number of benefits will accrue.
Michell quotes a book called Bore Hole written by Joseph (Joey) Mellen.  At the time the passage below was written, Joey and his partner, Amanda Feilding, had made two previous attempts at trepanning Joey.  The second attempt ended up placing Joey in the hospital, where he was scolded severely and sent for psychiatric evaluation.  After he returned home, Joey decided to try again.  Joey describes his third attempt at self-trepanation:
There is an active advocacy group for the self-trepanation procedure, the International Trepanation Advocacy Group.  Their webpage  includes MRI images of trepanned brains.

# Miscellaneous references
- A Hole in the Head is the 1998 documentary made about trepanation.
- In David Cronenberg's 1981 psychological thriller film Scanners, the leader of the rogue 'Scanner' organisation, Darryl Revok, practiced self trepanation to relieve the pressure of the telepathic voices in his head.
- In Philip Pullman's fantasy series His Dark Materials, trepanning is used by the Tartars to increase consciousness by attracting the mysterious substance called Dust.
- The movie  directed by Darren Aronofsky contains a somewhat graphic self-trepanation scene performed with an electric drill.
- The movie Saw III also contains a graphic trepanation scene.
- In the 2003 film Master and Commander: The Far Side of the World ship surgeon Stephen Maturin performs a trepanation on Joe Plaice whose skull was fractured by a falling piece of the yard arms.
- In the manga and anime One Piece trepanation is mentioned by the doctor Tony Tony Chopper as a method for treating tumours used in ancient times when analysing a skull they found in the wrecks of a pirate ship which fell from the sky.
- "Trephination" is a song by the trash metal band Machine Head.
- "Trepanning" is a song by the rock band Cave In.
- "Trepanation" is also the term used to refer to the process by which the steel in turbine rotors is tested for quality after forging.
- The band Ned's Atomic Dustbin named their 1995 album Brainbloodvolume. The album included a song named "Borehole".
- In the novel Dracula, Abraham Van Helsing uses trepanation to treat the haemorrhage Renfield received when Count Dracula flung him to the ground, in order to bring him back to consciousness.
- In the movie Frankenhooker, Jeffrey Franken (played by James Lorinz) trepans himself with a power drill to calm himself.
- In the movie Ghostbusters, Peter Venkman refers to a past incident when Egon attempted to drill a hole in his own head. Egon replies 'It would have worked if you hadn't stopped me.'
- In the movie X2: X-Men United, it is mentioned that the mother of Ronelio Ramil has drilled a hole in her head to drill out the visions that her son continuously projects into her mind. She did not survive the procedure.
- On the show Dead Like Me, Mason dies and becomes a grim reaper after attempting trepanation on himself while "chasing the ultimate high." 
- On the fourth season House episode "Frozen", Dr. Cate Milton (Mira Sorvino) undergoes a trepanning operation (with a drill press) at the South Pole conducted via webcam.
- On the third season of Grey's Anatomy, Izzie drills burr holes into a patient's head at a ferry boat crash scene.
- On the HBO/BBC series "Rome" season 1, episode 2 the character Titus Pullo undegoes the procedure to relieve him of swelling and to remove a jar fragment from his skull.  WARNING: This is an extremely graphic showing of the procedure.