Brain disorders

Brain disorder is a generic term for any and all of the numerous disorders associated with the human brain, including infections, stroke, seizures, trauma, cancer and other life-threatening diseases, autoimmune diseases, inherited disorders, neurodegenerative conditions, and growths such as tumors.

Most forms of mental illness, particularly those that are chronic, severe, or progressively debilitating (such as untreated schizophrenia) are also categorized as brain disorders. The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) is the most commonly used diagnostic reference tool in the United States for psychiatric illness; the International Classification of Diseases, Part 10 (ICD-10), which is used for both physical and mental illness, is used worldwide.

There are several types of infectious process that may directly affect brain function or cause brain diseases, the most common of which are: brain abscesses or infections within the structures of the brain; encephalitis, in which the brain tissue becomes inflamed as the result of a viral syndrome; and meningitis, which may be caused either by bacterial infection or a viral syndrome and results in inflammation of the lining of the spinal cord or brain tissue.

When an area of the brain experiences an abrupt interruption or cessation of blood flow during a stroke, the affected tissue often dies or is irreparably damaged, affecting the part(s) of the body controlled by that brain region. Bleeding in the brain, which may cause stroke or brain damage, can be caused by a ruptured aneurysm (extremely swollen blood vessel), subdural hematoma (usually trauma-related bleeding on the surface of the brain causing increased intracranial pressure), epidural hematoma (bleeding between the skull and the dura matter covering the brain), or any other type of bleeding inside the brain (intracerebral hemorrhage). Swelling in the brain caused by any means causes increased pressure and may result in stroke as well.

Seizures, whether caused by a seizure disorder such as epilepsy or occurring in isolated form such as febrile seizures (seizures caused by a very high fever during an illness), are considered brain disorders. When not well controlled or when lasting for more than just a couple of minutes, seizures can cause lasting damage to the brain. Seizures may be caused by infection, tumors, increased intracranial pressure, infections of the brain, stroke, or head trauma as well.

A significant head injury may result in increased pressure or bleeding within the brain. Traumatic brain injury, when moderate or severe, often results in lasting damage to the brain with resultant loss of cognitive or other (motor, visual, etc.) function, possible seizure disorder, mood and personality changes, and loss of function in the body regions associated with the damaged brain area. A concussion, depending upon severity, typically results in severe headaches and/or vision and memory problems and causes temporary changes in brain function; it may be associated with temporary loss of consciousness and changes in mental status.

Any abnormal growth within the brain or skull is called a tumor, but not all brain tumors are caused by cancer. Any unusual growth or excess fluid within the brain causes increased intracranial pressure. There are many types of cancer that either originate within the brain or metastasize from elsewhere (produce secondary tumors) and create cancerous lesions in the brain. Hydrocephalus is an increased amount of cerebrospinal fluid remaining inside the skull rather than circulating. It causes increased pressure and may result in permanent damage unless removed. Quite often in cases of hydrocephalus, a surgical procedure is performed in which a tube called a shunt is placed inside the skull to drain excess fluid from the brain into the abdominal cavity, where it can be harmlessly reabsorbed. A shunt may be permanent or a temporary drain may be used, depending on the cause of the hydrocephalus.

See also Alzheimer's disease ; Brain injuries ; Dementia ; Minimal brain dysfunction .


In the 1970s and 1980s, John Lorber, a neuroanatomist at Sheffield University in England, studied the effects of hydrocephalus (water on the brain) on individuals’ cognitive functions. Hydrocephalism occurs when pressure from cerebrospinal fluid causes the skull to enlarge, leading to loss of brain matter and causing impaired intellectual and physical faculties for many individuals with the condition. However, Lorber found that in some cases individuals with virtually no cortex (the outer layer of the brain) may experience little mental impairment.

In 1980, an article about Lorber's research was published in the journal Science, under the title “Is Your Brain Really Necessary?” The study centered on a student at Sheffield University who was observed to have a slightly above average head size. When Lorber examined him using neuroimaging, he was surprised to find that the student had virtually no brain. Most of his cranium was filled with cerebrospinal fluid. Despitethis, he had an IQ of 126, an honors degree in mathematics, and appeared to be well-adjusted socially. The student's cortex measured only a millimeter or so in thickness, compared to the normal 4.5 centimeters. This may seem extraordinary, but in fact there are similar anecdotes in historical medical literature. Lorber endeavored to gather a large set of data to explain this phenomenon.

Lorber specialized in patients with spina bifida, a congenital condition in which the spine does not fuse correctly, leaving nerve tissue exposed. Individuals with this condition often have hydrocephalism as a result. He conducted scans on 600 patients and found that of the most severe group (in which ventricle expansion and cerebrospinal fluid make up 95% of the space in the cranium), half had IQs greater than 100.

Lorber concluded from the studies that there must be a great deal of redundancy in the brain, as is the case in the liver and kidneys. Critics dispute these claims of spare capacity in the brain, saying that although there is generally plasticity and reallocation of functions in the brain in response to minor lesions, there is not redundancy. Others say that Lorber exaggerated the extent to which his subjects were lacking brain matter. Kenneth Till, a former neurosurgeon at the Great Ormond Street Hospital for Sick Children in London argues that “interpreting brain scans can be very tricky. There can be a great deal more brain tissue in the cranium than is immediately apparent.” He takes issue with Lorber's characterization of the patient as having “virtually no brain.” However, Lorber says, “I can't say whether the mathematics student has a brain weighing 50 grams or 150 grams, but it is clear that it is nowhere near the normal 1.5 kilograms.”

Lorber subsequently addressed a conference of pediatricians with a presentation entitled “Is Your Brain Really Necessary?” Although he concedes that this hyperbolic title was designed to get attention, and was an exaggeration, he maintains that his studies of hydrocephalic patients have demonstrated that the brain can function in conditions previously thought impossible. His studies have shown that even individuals who are severely lacking in cortical tissue may experience little noticeable mental impairment.



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