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Biology 202
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Visual Hallucinations: Another Argument for Brain Equals Behavior

Jennifer Cohen

A hallucination is defined as a sensory perception in the absence of an externally generated stimulus (4). They are different from illusions in that in an illusion an external object actually exists and is perceived, but is misinterpreted by the individual (4). Main forms of hallucinations are be visual, auditory, and olfactory, but since we have been discussing vision and interpretation of reality lately this paper will focus only on those that are visual. And I will attempt through the examination of two different types of visual hallucinations - release hallucinations and those experienced by schizophrenics - to make an argument for brain equals behavior.

Much work has been done to find the exact cause of hallucinations and what is going on in the brain when they occur. Some progress has been made. Charles Bonnet syndrome is the onset of hallucinations in psychologically healthy individuals who have recently become blind or seeing impaired. These are called release hallucinations because it is thought that they are 'released' or instigated by the, "removal of normal visual afferent impute to association cortex"(5). Experiments involving direct stimulation of the temporal lobe, and fMRI's taken during hallucinations have indicated that - at least for complex hallucinations - the cause may be that corresponding visual areas in the brain are activated in the absence of inhibition due to visual input. In other words, this is an example of the chicken with its head cut off - apparently normal visual input to areas of the brain responsible for interpreting different things may be the only thing that keeps us from experiencing hallucinations of this kind (5). An fMRI study of persons with Charles Bonnet syndrome found a very high correlation between the types of hallucinations experienced by these patients and increased activity in the corresponding visual area of their brains. For example, patients hallucinating in color showed activity in an area known to be the color center in the fusiform gyrus while a patient hallucinating in black and white showed activity outside of this region (3). Likewise, activity was found in the middle fusiform gyrus which responds to visual objects in a patient who hallucinated objects, and in the collateral sulcus which responds to visual textures in patients who hallucinated things like fences and brickwork (3). So it seems that whatever is responsible for hallucinations of this sort stimulates them through the same means we use to interpret our visual reality under normal circumstances.

These hallucinations are experienced identically to normal seeing, however they are distinguishable from reality because of their content and the fact that they often appear in clearer and greater detail than Charles Bonnet patients (whose visions have been impaired or lost) would naturally see (3). These "release" hallucinations are often not reported to doctors and psychologists because the individuals experiencing them are aware that what they are seeing are hallucinations and are afraid of being judged as crazy by those people that they might tell (5).

These are different from the visual hallucinations experienced by people suffering from schizophrenia because schizophrenics most often cannot differentiate their hallucinations from reality. It was hypothesized that in schizophrenics hallucinations occurred as a result of "confusing external and internal stimulus sources" (2). In a study conducted to test this hypothesis, it was found that hallucinations might be a result of a higher level of vividness of patients' mental imagery. In addition, the more impaired a patient's affinity for reality discrimination, the higher the severity of the hallucinations (2).

This poses another interesting argument for "brain equals behavior". When I first read about Charles Bonnet syndrome I thought I'd found a contradictory example. It seemed to me that if these patients were experiencing hallucinations that are sensorilly identical to seeing and yet are able to distinguish them and not respond as if they were real then they were behaving in opposition to what their brain was trying to tell them.

But what becomes clear when we look at schizophrenic hallucinations is that people suffering from Charles Bonnet syndrome are not acting contrary to their brain function. Rather they have and are still driven by other parts of their brain that tell them that the hallucination isn't real. Schizophrenics cannot do this. Even if they know they hallucinate, they still cannot tell their hallucinations apart from reality (1). Their hallucinations affect their behavior because they have nothing in their brain telling them not to be affected by them. Charles Bonnet sufferers do, and an important thing to remember is that just because they don't respond to their hallucinations as if they were real does not mean that they do not affect their behavior. These people do take notice of their hallucinations; they watch them, spend time interpreting them, and often think about them afterwards. This is behavior different than that which would be exhibited in a non-hallucinating individual and so their altered brain function does indeed influence their behavior.

The most fundamental detail, however, which flew completely over my head when I was first looking at this problem, is that the hallucinations themselves are a behavioral manifestation of brain function. Just as is interpreting reality the way we do. Sight as we know it is a result of neural functioning and so may be thought of as a behavior. By this logic, a deviation in the way we see or perceive also produces perception that is a type of behavior.

So as is shown here by the examples of schizophrenic hallucinations versus those experienced in Charles Bonnet syndrome, you do not have to act as if your hallucinations are real in order to be responding to them behaviorally. Indeed, all you have to do is have them in order to behave as your brain is telling you to. So yet again in an attempt to find an argument for something more I guess I have found one more thing that argues brain does indeed equal behavior.

WWW Sources

1)abcNEWS.com. , New Treatments for Schizophrenia

2)British Journal of Clinical Psychology 2000,Perception, mental imagery, and reality discriminations. . .

3)The Anatomy of Conscious Vision

4)Introduction to Psychopathology

5)Survey of Opthalmology




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