Visual[edit]

Visual hallucination is the 'seeing of things that are not there'[3] which can also (according to some definitions) include

'seeing things that are there, incorrectly' (Illusions).

Auditory[edit]

Main article: Auditory hallucination

Auditory hallucinations (also known as paracusia)[4] are the perception of sound without outside stimulus. Auditory

hallucinations can be divided into two categories: elementary and complex. Elementary hallucinations are the perception

of sounds such as hissing, whistling, an extended tone, and more. In many cases, tinnitus is an elementary auditory

hallucination. However, some people who experience certain types of tinnitus, especially pulsatile tinnitus, are actually

hearing the blood rushing through vessels near the ear. Because the auditory stimulus is present in this situation, it does

not qualify as a hallucination.

Olfactory[edit]

Phantosmia is the phenomenon of smelling odors that aren't really present. The most common odors are unpleasant

smells such as rotting flesh, vomit, urine, feces, smoke, or others. Phantosmia often results from damage to the nervous

tissue in the olfactory system. The damage can be caused by viral infection,brain tumor, trauma, surgery, and possibly

exposure to toxins or drugs.[13] Phantosmia can also be induced by epilepsy affecting the olfactory cortex and is also

thought to possibly have psychiatric origins.[citation needed] Phantosmia is different from parosmia, in which a smell is actually

present, but perceived differently from its actual smell.

Olfactory hallucinations can also appear in some cases of associative imagination, for example, while watching a romance

movie, where the man gifts roses to the woman, the viewer senses the roses' odor (which in fact does not exist).

Olfactory hallucinations have also been reported in migraine, although the frequency of such hallucinations is unclear.[14][15]

Tactile hallucinations[edit]

Tactile hallucinations are the illusion of tactile sensory input, simulating various types of pressure to the skin or other

organs. One subtype of tactile hallucination, formication, is the sensation of insects crawling underneath the skin and is

frequently associated with prolonged cocaine or amphetamineuse[16] or with withdrawal from alcohol or benzodiazepines.

However, formication may also be the result of normal hormonal changes such as menopause, or disorders such

as peripheral neuropathy, high fevers, Lyme disease, skin cancer, and more.[16]

Gustatory[edit]

This type of hallucination is the perception of taste without a stimulus. These hallucinations, which are typically strange or

unpleasant, are relatively common among individuals who have certain types of focal epilepsy, especially temporal lobe

epilepsy. The regions of the brain responsible for gustatory hallucination in this case are the insula and the superior bank

of the sylvian fissure.[17][18]

General somatic sensations[edit]

General somatic sensations of a hallucinatory nature are experienced when an individual feels that his body is being

mutilated i.e. twisted, torn, or disembowelled. Other reported cases are invasion by animals in the person's internal organs

such as snakes in the stomach or frogs in the rectum. The general feeling that one's flesh is decomposing is also

classified under this type of hallucination.[19]

Hallucinations can be caused by a number of factors.

Hypnagogic hallucination[edit]

Main article: Hypnagogia

These hallucinations occur just before falling asleep, and affect a surprisingly high proportion of the population (in one

survey 37% of the respondents experienced them twice a week [20]). The hallucinations can last from seconds to minutes,

all the while the subject usually remains aware of the true nature of the images. These may be associated

with narcolepsy. Hypnagogic hallucinations are sometimes associated with brainstem abnormalities, but this is rare.[21]

Alice-in-Wonderland syndrome (AIWS, named after the novel written by Lewis Carroll), also known as Todd's syndrome[1] or lilliputian hallucinations, is a disorienting neurological condition that affects human perception. Sufferers may experience micropsia, macropsia, or size distortion of other sensory modalities. A temporary condition, it is often associated with migraines, brain tumors, and the use of psychoactive drugs. It can also present as the initial sign of the Epstein-Barr Virus (see mononucleosis).[2] Anecdotal reports suggest that the symptoms of AIWS are fairly common in childhood,[citation needed] with many people growing out of them in their teens. It appears that AIWS is also a common experience at sleep onset. Alice in Wonderland Syndrome can be caused by abnormal amounts of electrical activity causing abnormal blood flow in the parts of the brain that process visual perception and texture.[3]

hallucination /hal·lu·ci·na·tion/ (hah-loo″sĭ-na´shun) a sense perception (sight, touch, sound, smell, or taste) that has no basis in external stimulation.hallu´cinativehallu´cinatory

haptic hallucination  tactile h.

kinesthetic hallucination  a hallucination involving the sense of bodily movement.

somatic hallucination  a hallucination involving the perception of a physical experience with the body.

hypnagogic hallucination  one occurring just at the onset of sleep.

hypnopompic hallucination  one occurring during awakening.

tactile hallucination  one involving the sense of touch.

Anterograde amnesia refers to the inability to create new memories due to brain damage, while long-term memories

from before the event remain intact. The brain damage can be caused by the effects of long-term alcoholism, severe

malnutrition, stroke, head trauma, surgery, Wernicke-Korsakoff Syndrome, cerebrovascular events, anoxia or other

trauma.[16] The two brain regions related with this condition are medial temporal lobe and medial diencephalon.

Anterograde amnesia can't be treated with pharmacological methods due to neuronal loss.[17] However, treatment

exists in educating patients to define their daily routines and after several steps they begin to benefit from their

procedural memory. Likewise, social and emotional support is critical to improving quality of life for anterograde

amnesia sufferers.[17]

Retrograde amnesia refers to inability to recall memories before onset of amnesia. One may be able to encode new

memories after the incident. Retrograde is usually caused by head trauma or brain damage to parts of the brain

besides the hippocampus. The hippocampus is responsible for encoding new memory. Episodic memory is more

likely to be affected than semantic memory. The damage is usually caused by head trauma, cerebrovascular

accident, stroke, tumor, hypoxia, encephalitis, or chronic alcoholism. People suffering from retrograde amnesia are

more likely to remember general knowledge rather than specifics. Recent memories are less likely to be recovered,

but older memories will be easier to recall due to strengthening over time.[18] Retrograde amnesia is usually temporary

and can be treated by exposing them to memories from the loss.[19] Another type of consolidation (process by which

memories become stable in the brain) occurs over much longer periods of time/days, weeks, months and years and

likely involves transfer of information from the hippocampus to more permanent storage site in the cortex. The

operation of this longer-term consolidation process is seen in the retrograde amnesia of patients with hippocampal

damage who can recall memories from childhood relatively normally, but are impaired when recalling experiences

that occurred just a few years prior to the time they became amnesic. (Kirwan et al.,2008)

Post-traumatic amnesia is generally due to a head injury (example: a fall, a knock on the head). Traumatic

amnesia is often transient, but may be permanent or either anterograde, retrograde, or mixed type. The extent of

the period covered by the amnesia is related to the degree of injury and may give an indication of the prognosis

for recovery of other functions.