"Brain damage" or "brain injury" (BI) is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors. A common category with the greatest number of injuries is traumatic brain injury (TBI) following physical trauma or head injury from an outside source, and the term acquired brain injury (ABI) is used in appropriate circles, to differentiate brain injuries occurring after birth, from injury due to a disorder or congenital malady.
Brain injuries often create impairment or disability which can vary greatly in severity. In cases of serious brain injuries, the likelihood of areas with permanent disability is great, including neurocognitive deficits, delusions (often specifically monothematic delusions), speech or movement problems, and mental handicap. There will also be personality changes. The most severe cases result in coma or even persistent vegetative state. Even a mild incident can have long term effects or cause symptoms to appear years later.
Mental fatigue is a common debilitating experience and may not be linked by the patient to the original (minor) incident. Narcolepsy and sleep disorders are common misdiagnoses.
Brain injury whether from stroke, alcohol abuse, traumatic brain injury, or vitamin B deficiency can sometimes result in Korsakoff's Psychosis, where the individual engages in confabulations. Confabulations involve the inability to separate daydream memory from real memory and the filling in of memory lapses with daydreams. Like all other symptoms of brain injuries, Korsakoff's Psychosis is often mis-diagnosed, in this case as schizophrenia.
Brain injuries occur due to a very wide range of conditions, illnesses, injuries, and as a result of iatrogenesis (adverse effects of medical treatment). Possible causes of widespread (diffuse) brain damage include prolonged hypoxia (shortage of oxygen), poisoning by teratogens (including alcohol), infection, and neurological illness. Chemotherapy can cause brain damage to the neural stem cells and oligodendrocyte cells that produce myelin. Common causes of focal or localized brain damage are physical trauma (traumatic brain injury, stroke, aneurysm, surgery, other neurological disorder), and heavy metals causing poisoning including by mercury and its compounds of lead or blows to the back of skull.
Various professions may be involved in the medical care and rehabilitation of someone who suffers impairment after a brain injury. Neurologists, neurosurgeons, and physiatrists are physicians who specialise in treating brain injury. Neuropsychologists (especially clinical neuropsychologists) are psychologists who specialise in understanding the effects of brain injury and may be involved in assessing the severity or creating rehabilitation strategies. Occupational therapists may be involved in running rehabilitation programs to help restore lost function or help re-learn essential skills. Registered nurses, such as those working in hospital intensive care units, are able to maintain the health of the severely brain-injured with constant administration of medication and neurological monitoring, including the use of the Glasgow Coma Scale used by other health professionals to quantify extent of orientation.
The effects of impairment or disability resulting from brain injury may be treated by a number of methods, including medication, psychotherapy, neuropsychological rehabilitation, snoezelen, surgery, or physical implants such as deep brain stimulation.
Prognosis, or the likely progress of a disorder, depends on the nature, location and cause of the brain damage (see Traumatic brain injury).
In general, neuroregeneration can occur in the peripheral nervous system but is much rarer and more difficult to assist in the central nervous system (brain or spinal cord). However, in neural development in humans, areas of the brain can learn to compensate for other damaged areas, and may increase in size and complexity and even change function, just as someone who loses a sense may gain increased acuity in another sense - a process termed neuroplasticity.
It is a common misconception that a brain injury sustained during childhood always has a better chance of successful recovery than similar injury acquired in adult life. It is contested that in recent studies, severe brain injuries inflicted upon children can be alleviated by the interaction of nicotinamide repropagation in nerve cells. However, the consequences of childhood injury may simply be more difficult to detect in the short term. This is because different cortical areas mature at different stages, with some major cell populations and their corresponding cognitive faculties remaining unrefined until early adulthood. In the case of a child with frontal brain injury, for example, the impact of the damage may be undetectable until that child fails to develop normal executive functions in his or her late teens and early twenties.