Sometimes internal imagery can overwhelm the sensory input from external stimuli when sharing neural pathways, or if indistinct stimuli is perceived and manipulated to match one's expectations or beliefs, especially about the environment. This can result in a hallucination, and this effect is sometimes exploited to form an optical illusion.
There are 3 pathophysiologic mechanisms thought to account for complex visual hallucinations theses mechanisms consist of the following:
The first mechanism involves irritation of cortical centers responsible for visual processing (e.g., seizure activity). The irritation of the primary visual cortex causes simple elementary visual hallucinations.
The second mechanism involves lesions that cause deafferentation of the visual system may lead to cortical release phenomenon, which includes visual hallucination.
The third mechanism is the reticular activating system, which has been linked to the genesis of visual hallucinations.
Some specific classifications include: elementary hallucinations, which may entail flicks, specks, and bars of light (called phosphenes). Closed eye hallucinations in darkness, which are common to psychedelic drugs (i.e., LSD, mescaline). Scenic or "panoramic" hallucinations, which are not superimposed but vividly replace the entire visual field with hallucinatory content similarly to dreams; such scenic hallucinations may occur in epilepsy (in which they are usually stereotyped and experimental in character), hallucinogen use, and more rarely in catatonic schizophrenia (cf. oneirophrenia), mania, and brainstem lesions, amongst others.
Another thing that may cause visual hallucinations is prolonged visual deprivation. Which a study was done where 13 healthy people were blindfolded for a period of 5 days and 10 out of the 13 subjects reported visual hallucinations. This finding lends strong support to the idea that the simple loss of normal visual input is sufficient to cause visual hallucinations.
Various theories have been put forward to explain the occurrence of hallucinations. When psychodynamic (Freudian) theories were popular in psychology, hallucinations were seen as a projection of unconscious wishes, thoughts and wants. As biological theories have become orthodox, hallucinations are more often thought of (by psychologists at least) as being caused by functional deficits in the brain. With reference to mental illness, the function (or dysfunction) of the neurotransmitters glutamate and dopamine are thought to be particularly important. The Freudian interpretation may have an aspect of truth, as the biological hypothesis explains the physical interactions in the brain, while the Freudian deals with the origin of the theme of the hallucination. Psychological research has argued that hallucinations may result from biases in what are known as metacognitive abilities.
INFORMATION PROCESSING PERSPECTIVE
These are abilities that allow us to monitor or draw inferences from our own internal psychological states (such as intentions, memories, beliefs and thoughts). The ability to discriminate between internal (self-generated) and external (stimuli) sources of information is considered to be an important metacognitive skill, but one which may break down to cause hallucinatory experiences. Projection of an internal state (or a person's own reaction to another's) may arise in the form of hallucinations, especially auditory hallucinations. A recent hypothesis that is gaining acceptance concerns the role of overactive top-down processing, or strong perceptual expectations, that can generate spontaneous perceptual output (that is, hallucination).
Stages of Hallucination
- Emergence of surprising or warded-off memory or fantasy images
- Frequent reality checks
- Last vestige of insight as hallucinations become "real"
- Fantasy and distortion elaborated upon and confused with actual perception
- Internal-external boundaries destroyed and possible pantheistic (or personally felt or believed, possibly profound, internal spiritual or religious) experience
VISUAL The most common modality referred to when people speak of hallucinations. These include the phenomena of seeing things which are not present or visual perception which does not reconcile with the physical, consensus reality. There are many different causes, which have been classed as psychophysiologic (a disturbance of brain structure), psychobiochemical (a disturbance of neurotransmitters), psychodynamic (an emergence of the unconscious into consciousness), and psychological (e.g. meaningful experiences consciousness), this is also the case in Alzheimer's disease. Numerous disorders can involve visual hallucinations, ranging from psychotic disorders to dementia to migraine, but experiencing visual hallucinations does not in itself mean there is necessarily a disorder. Visual hallucinations are associated with organic disorders of the brain and with drug- and alcohol-related illness, and not typically considered the result of a psychiatric disorder.
SCHIZOPHRENIC HALLUCINATION Hallucinations caused by schizophrenia. Schizophrenia is when one is unable to tell the difference between real and unreal experiences, accompanied by the inability to think logically, have contextually appropriate emotions, and to function in social situations. Scientifically reviewed. 21 October 2012. Web. It has been found that when one experiences a hallucination induced by Schizophrenia, there are many abnormalities that are going on in the brain; Particularly in the region that processes voices in sounds (for those who experience auditory hallucinations) and visual processing. (visual hallucinations). According to studies and experiments conducted by researchers, it was seen that a possible cause for these hallucinations were abnormalities in gray matter and general functioning that combines interpreting sounds, voices and visuals, as well as regulating emotions.
NEUROANATOMICAL CORRELATES Normal everyday procedures like getting an MRI (Magnetic Resonance Imaging) have been used to find out more about auditory and verbal hallucinations. "Functional magnetic resonance imaging (fMRI) and repetitive transcranial magnetic stimulation (rTMS) were used to explore the pathophysiology of auditory/verbal hallucinations (AVHs)" Throughout the exploring through MRI's of patients,there were "lower levels of hallucination-related activation in Broca’s area strongly predicted greater rate of response to left temporoparietal rTMS." What these findings could suggest is that "dominant hemisphere temporoparietal areas are involved in expressing AVHs, with higher levels of coactivation and/or coupling involving inferior frontal regions reinforcing underlying pathophysiology."
Also through fMRI's, it is found that there can be better understandings on why hallucinations happen in the brain, by understanding emotion's and cognition and how it can prompt physical reactions that can help result in a hallucination. It suggests the theory that "motivations in the body and mind can drive us to certain behaviors that we act in, such as survival instinct and intuition" and that they can work in a hand in hand like fashion. It can also be viewed as a symbolic "homeostasis" that can have adverse effects by having these hallucinations and / or mental illnesses. The amygdlada has also been seen to relate to this finding by contributing a "declarative judgement of emotional salience" as well as affecting both "efferent and afferent representational levels of affective autonomic responses in the brain".
PATHOPHYSIOLOGICAL MECHANISMS "The left superior temporal cortex, which supports linguistic functions, has consistently been reported to activate during auditory–verbal hallucinations in schizophrenia patients" The Charles Bonnet Syndrome supports the visual cortex cortex deafferentiation proposal. There is irritation in the visual cortex when hallucination occur, which could suggest why it is reported that images that are not real are seen. Although many sufferers of the Charles Bonnet Syndrome are elderly, it can occur in anyone. The reticular activation system can be used to support the neurotransmitters (dopamine and norepinephrine) effect on hallucinations.
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