There are a number of rare mental disorders, with a variety of causes ranging from brain damage to deterioration. Foreign accent syndrome has an effect on language, while hemispheric malpractice causes changes in vision. Capgras and Korsakov syndromes both have a profound effect upon memory, while still other disorders can cause paralysis, delusions, and other significant physical and emotional changes.
Foreign accent syndrome is one of several rare mental disorders that occur due to damage in the left side of the brain, where language control originates. Individuals may speak with an accent from a different country or even develop his or her own language. Some patients may begin speaking an unrecognizable language that is a mixture of several different languages that the individual has experienced.
Some rare mental disorders may also affect the memory. Capgras syndrome deals with identification. An individual suffering from this disease will see the face of a loved one, but feel they are an impostor. When a stranger is present the individual will sometimes react as if that person is familiar. Scientists believe Capgras syndrome occurs because of a disconnection with visual recognition and emotional memory.
Korsakov syndrome is another disorder that affects memory. This is commonly caused by chronic alcoholism, and causes amnesia of short term memory. The individual cannot remember new experiences or facts, and can only recall memories and information stored before the disorder began.
Hemispheric malpractice is caused by deterioration of the parts of the brain that deal with vision. Patients will only be able to see things in half. For example, patients suffering from this disorder will only see half of a book page, eat half of a meal, or tie one shoe but not the other.
Some rare mental disorders may also cause paralysis. Anasognosia results in paralysis of the left side of the body due to damage of the brain's right side. There are some instances in which the individual has a paralyzed left side but firmly believes that the left arm has moved and performed tasks, even though the arm cannot move.
Research has uncovered rare mental disorders that affect social skills as well. Olfactory reference syndrome, or ORS, is a mental disease in which patients believe they exude an offensive body odor when they do not. This belief causes individuals to become anti-social, and some have been known to contemplate suicide.
The walking corpse syndrome, or Cotard delusion, is a neuropsychiatric disorder. Patients believe that key internal organs in their bodies do not exist or are dead. In some very rare instances, they may also believe in their immortality, with symptoms ranging from mild to severe. This disorder is thought to be due to a disconnection in the brain, similar to Capgras syndrome.