Dementia and the Implications of Resulting Altered Neurophysiology on the Concepts of Reality and the Self

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Biology 202, Spring 2005
Second Web Papers
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Dementia and the Implications of Resulting Altered Neurophysiology on the Concepts of Reality and the Self

Liz Bitler

Currently, over 20 million people are affected by dementia (1). Dementia occurs in individuals when the activity of brain cells is altered and the brain functions differently. Language ability, memory capabilities, visual-spatial perception, emotional behavior or personality, and/or cognitive skills may be altered as a result of dementia (2). Because dementia results in an altered mind state, it is a topic of much interest in the consideration of neurophysiology and brain function in terms of the I-function. That is to say, what is it about the changes in the brain associated with dementia that result in changes in the mind?

Dementia is associated with several different diseases, many of which have both specific and overlapping physiological sources and symptoms. Generally, it can be stated that dementia is caused by altered levels of neurotransmitters (3), damage to tissues from either vascular (2) or metabolic (4) causes, or damage to neural cells from the entanglement of neurons or intracellular lesions (1). The general symptoms associated with dementia include: memory loss, lack of attention, confusion, decrease in problem-solving skills, decreased judgment capabilities, hallucinations, delusions, altered sensation or perception, agnosia, altered sleep patterns, motor system impairment, disorientation, impaired language ability, and personality changes (such as increased irritability, poor temper control, anxiety, depression, self-centeredness, inappropriate mood, inability to function in social or personal situations, decreased ability to care for oneself) (2).

Alzheimer's Disease (AD)

Alzheimer's disease affects approximately 4 million people (5), and nearly 50% of all people over the age of 85 (6). It is the most common disease associated with dementia. There are several sources of AD in the elderly. Recently, it has been found that there is a strong correlation between high cholesterol (due to the apolipoprotein-E4 allele, which results in increased levels of amyloid beta-peptide) and AD (7). One of the neurological changes frequently observed in patients with AD is neuritis plaques, which occur when protein deposits build up on neurons and prevent them from properly functioning, or destroy them completely (8). Plaque on ACh containing nerve cells (which contain the amyloid protein) are particularly damaging to the proper functions of the brain and result in altered levels of ACh, a neurotransmitter, which may then result in altered levels of awareness and subsequent dementia (9). ACh has been linked to the efficiency of interpreting sensory and cognitive information, as well as for sustaining the sensation of experience and awareness (3). Another particularly interesting cause of AD is the presence of abnormal tau genes. The tau gene (FTDP-17) is linked to chromosome 17, and may become filamentous and result in entangled neurons. The entangled neurons then form masses in the brain and prevent normal functioning (1). AD may also be caused by neuronal and synapse loss (3) or other deficits in the cholinergic system (which is discussed in greater detail below.)

Lewy Body Dementia (LBD)

Lewy Body Dementia is the second most frequent cause of dementia. This disease is marked by the presence of Lewy bodies in various regions of the brain (10). Lewy Bodies are abnormal neural structures that result from the deposit of one of three possible proteins: alpha synuclein, parkin and/or ubiquitin (9). Other noted neurological alterations associated with LBD include changes in the basal ganglia (9), which result in a reduction in the number of cholinergic projections to the thalamic reticular nucleus, which then in turn results in a reduction of the potential cholinergic neurotransmission. Decreased ACh activity has also been observed in patients with LBD, and this may be tied in with the decreased function of cholinergic neurotransmission. Specific to LBD is the correlation between hallucinations and decreased cholinergic function, as well as "absence episodes," during which the individual experiences a lowered level of consciousness while awake. (3)

Vascular Dementia

Vascular dementia accounts for 10-20% of all cases of dementia (5). It occurs when there is a loss of brain function as a result of a stroke or a series of small strokes (2). Multi-infarct dementia (MID) is the most common type of vascular dementia. MID is specifically the resulting damage of multiple regions of the brain from a lack of oxygen (11). A stroke takes place when blood flow is disrupted, causing an inefficient amount of blood to be delivered to the brain to sustain neural activity (5). Because MID is caused by strokes, the causes reflect those of strokes, such as smoking, high blood pressure, and diabetes (2).

Parkinson's Disease (PD)

PD is another disease that is marked by dementia. Deficits in cholinergic neurotransmission are largely responsible for the effects of PD. This may occur in one of various manners. There may be a loss of pedunoculopontine cholinergic neurons (3), which equates to a loss of the neurons that produce important neurotransmitters such as dopamine, norephinephrine, or ACh (9). There may also be other problems in the neurotransmission process, such as an inability for the ACh transporting ions to bind to receptor molecules (3). Similarly to some observed patients with AD, there is also a presence of abnormal tau genes in a sizable proportion of patients with PD (1).

Fronto-temporal Dementia (FTD) aka Pick's Disease and Binswanger's Disease

Little is known about either Pick's Disease or Binswanger's Disease other than a few possible causes, which have been identified because of similar observations in patients with other dementia-causing neurological conditions. Among the proposed causes of Pick's disease are the filamentous tau (1) and resulting neuro-fibrillary tangles (9) and also observed atrophy in the frontal and temporal lobes (12). Cardiovascular lesions have been observed in the white matter of Binswanger's Disease patients, and the dementia has been attributed to that particular neural structure damage. Specific dementia symptoms of Binswanger's Disease patients are memory loss, loss of cognitive function, and notable mood changes. (13)

Cholingelic System

The cholingelic system is of much importance to the study of dementia because it is an extensive neurotransmitter system that has been shown to affect conscious awareness. The system consists of projections throughout the central nervous system, particularly in the cortex and the thalamus. (3) Experimentation results show that altering the cholinergic inputs results in an alteration of cognitive function. More importantly for the discussion of dementia, it has been observed that abnormalities in the regulation of such inputs results in an increased likelihood of acquiring attentional dysfunctions. (14)

Discussion of Possible Implications

Dementia results from altered neurology of and individual, and it provides a clear example for the concept that as the neurology of an individual is altered, their perceptions and cognition of the world around them is altered as well. Because one's concept of reality is tailored to their particular experiences and understanding of the world, each person has a different idea of what is "real." However, it is important to note that there are some underlying facts beyond individual different realities. For example, when presented with a painting, two individuals may perceive the same painting very differently. Yet it remains undisputed by any individual with normal neurological functioning that they perceive the painting in front of them, that is to say that they can see it or reach out and touch it (the argument as to whether or not it is really there should be left to Descartes and Kant.) One of the most devastating results of dementia is the loss of the underlying reality. People with dementia may go beyond perceiving a painting differently to not perceiving it at all, or even to perceiving a painting that doesn't exist. When the topic of dementia is brought up among friends and families of those affected, many say that their loved ones are no longer themselves. They may loose their ability to remember names, places, and events, their behavior may change drastically, and their realities may become completely altered from their previous conceptions. If what makes a person unique and an individual is their I-function and their distinct perceptions and cognitions of the world, then dementia has the ability of killing an individual on a level much greater than the physical death due to associated diseases.