Welcome to the educational program Memory Impairment: Risk Factors. This program will provide a basic understanding of how memory works and the different kinds of memory. It will also discuss some risk factors for memory loss and how they can interfere with normal memory functioning.
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You may view the topics in order as presented, or click on any topic listed in the main menu to be taken to that section.
We hope that you enjoy this program and find it useful in helping both yourself and those you care for. There are no easy answers when it comes to the care of another, as every situation and person is different. In addition, every caregiver comes with different experiences, skills, and attitudes about caregiving. Our hope is to offer you useful information and guidelines for caring for someone with dementia, but these guidelines will need to be adjusted to suit your own individual needs. Remember that your life experiences, your compassion and your inventiveness will go a long way toward enabling you to provide quality care.
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How Memory Works
Let’s take a look at what happens in the brain to make memory possible. Several specialized areas in the brain, such as the hippocampus, are responsible for processing, storing, and retrieving memories. Although there is a lot of research on how memory works, much is still unknown. The important things to remember about memory is that it is subjective, and people only store information that they are paying attention to.
The brain is made up of trillions of nerve cells, called neurons. Each of these nerve cells has antenna-like structures called axons and dendrites that reach out to other axons and dendrites. This reaching out establishes the pathways of information that allow communication between nerve cells in different parts of the brain and the body.
Millions of nerve cells make up what is called the gray matter of the brain, which forms the outer portion of the brain. Gray matter contains the processing centers for the brain’s functions. In Alzheimer’s disease, it is primarily the gray matter that is lost in various parts of the brain.
The deeper white matter of the brain is made up of the fibrous axons that reach out to other nerve cells. These axons are covered with a myelin sheath, which is a whitish fatty coating that insulates them, allowing signals to travel more efficiently along the nerve fiber. Millions of these myelinated nerve fibers form a structure called the corpus callosum, which connect the left and right sides of the brain to allow efficient communication between them. In some forms of dementia, such as vascular dementia, areas of the myelin sheath usually suffer damage and break down, causing the brain to lose its ability to transmit information.
How Memory Works (Part 2)
When babies are born, they do not have fully developed brains. The nerve fibers do not have fully developed insulation called myelin sheaths. Because of this, thoughts and memories are erratic. As the myelin sheath develops, the nerve cells, also called neurons, are able to send signals more efficiently and form connections with other nerve cells.
Forming connections and networks of nerve cells is a tricky process because the axon of one nerve cell is not physically connected to other nerve cells, but rather, there is a minuscule space between them called a synapse. When a signal in a nerve cell travels from the dendrite to the cell body and onto the end of an axon, chemicals called neurotransmitters are released. Neurotransmitters leave the axon and cross the synapse to get picked up by a dendrite of the next neuron. When enough neurotransmitters are picked up by the receiving nerve cell, it triggers a signal that travels down this new nerve cell to cause the release of new neurotransmitters from its axon. This cascade of nerve cell firing and neurotransmitter release is how one nerve cells sends a signal to the next nerve cell and so on.
The signal that travels from the dendrite to the cell body and axon is called an action potential. A complex pattern of action potentials through networks of nerve cells and pathways is how information is stored and transmitted in the brain.
In Alzheimer’s disease, the brain produces less neurotransmitters, affecting the ability to transmit information and make new connections between nerve cells. Over time, nerve cell networks and pathways are damaged and lost, resulting in loss of the abilities to understand, learn new information, and retrieve old information.
How Memory Works (Part 3)
Memory is the ability to retain and recall information. Memory and learning are closely related and involve complex processes of information association and storage. For example, a child can learn a new word by pairing a visual image with auditory sound information, which causes two pathways of brain cells in the brain to fire at the same time. For example, if the child sees a bird and hears someone say “dove,” an association between the visual and auditory pathways is made, and learning occurs. The more this information is rehearsed, the better the memory for this association.
In order to become a memory, all information must go through three steps: Encoding, which is the process of registering the information; Storage, which creates a permanent record of the encoded information; and Retrieval, which is calling back the stored information.
Information is first acquired, then passed into short-term memory. Short term memory allows recall for a period of several seconds to a minute without rehearsal. The rehearsal or repeated exposure to information can lead to memory consolidation, which is the process by which recent or short-term memories are transformed into long-term memories.
Memory consolidation occurs through repeated firing of pathways in the brain that strengthens connections between a network of nerve cells and their pattern of firing, giving meaning to information and storing it.
With continued rehearsal, or repeated firings between a network of nerve cells, the connections become stronger, allowing the information to remain in storage forever in some cases.
After information is encoded and stored, information must be retrievable in order to remember it. Retrieval is a process of accessing stored memories. There are four types of memory retrieval.
Recall involves being able to access the information without being provided with any part of the memory. For example, answering fill-in-the-blank questions on a test require recall of information.
Recollection involves reconstructing a memory of a fact or event using pieces of memories, and oftentimes, clues, logical structure, and narrative. An example that involves recollecting information is answering an essay question. Recognition is identifying information as a memory after experiencing it again. For instance, answering multiple choice or matching questions require recognition of learned information.
Relearning involves relearning information that has been previously learned, which often strengthens the memory and makes it easier to remember and retrieve the information in the future.
Retrieved information is often not a faithful reproduction of the original information. During retrieval, people use a variety of strategies to generate a consistent and coherent memory, including comparison, inferences, shrewd guesses, and suppositions. Research shows that people tend to reorder, reconstruct and condense information to fit their own perceptions. It is not a conscious process, as when someone lies, but it is an unconscious process influenced by the rules that people acquire through their experiences, education, culture and beliefs. These rules automatically transform information as it is perceived as well. As individuals grow and develop, family values, culture, and education allow them to specialize their brains to process and use information in terms of their own unique values, knowledge, and behaviors.
Types of Memory
There are many different types of memory. The four main types are sensory memory, explicit memory, implicit memory, and spatial memory.
Sensory memory is a type of short-term memory for sensory information after the original stimulus is no longer there. It is based on information that is received through the sensory organs: the eyes, nose, skin, tongue, or ears.
The two most common types of sensory memory are iconic memory, or the brief mental picture after seeing something, and echoic memory, or the brief mental echo of a sound after it is heard. For example, iconic memory can be the memory of a phone number that you looked up in a phonebook just before picking up the telephone and dialing the number.
Another type of memory is called explicit memory, or the “what it is” of information. Explicit memory, also referred to as declarative memory, involves the conscious, intentional recollection of information and past events. It includes knowing that the world is round and that spring follows winter. Explicit memories encompass acquired knowledge and facts about the world, people, places, objects, and events including life events that can be recalled and talked about. Explicit memory can be broken down even further into episodic memory and semantic memory.
In contrast to episodic memory, semantic memory refers to the memory of meanings, understandings, and other concept-based knowledge that is not unrelated to specific experiences. It is the generic, context-free, encyclopedic knowledge that a person acquires over a lifetime about things. In semantic memory, the brain stores information about words, what they mean, and how they are used.
The good news is that aging is not associated with loss of semantic memories. This store of memories become a part of the general knowledge base that people usually can’t recall learning. So if an elderly person is given enough time, the quality of the recalled semantic memories are adequate.
Implicit Memory and Spatial Memory
Implicit memory involves remembering things without being aware that you are remembering them. It is an automatic or an unconscious form of memory. Previous experiences help in performing a task, so that your performance improves with repetition, but you are consciously aware of these previous experiences. There are many forms of implicit memory. One form is called procedural or motor memory, which refers to knowing how to physically perform tasks, such as walking, riding a bicycle, tying shoelaces, and dressing. Implicit memories are commonly lost in the later stages of Alzheimer’s disease.
The last type of memory is spatial memory. It is the part of memory that stores information about one’s environment and its spatial orientation. Spatial memory appears to decline with aging. For example, finding an address even in a familiar part of a city becomes harder for the elderly. Missing a step, bumping into objects, getting lost in the parking lot become more frequent occurrences with aging. Awareness of where parts of the body are in space and where one is in relation to other people or dangerous objects become more difficult for elders and can become potential hazards.
Because these types of memories are distinct, impairment of one may not involve the impairment of another. For example, a person might be able to recall words, events, and stories, but not be able to manipulate the information to devise a plan and carry it out. This knowledge can be an important factor in caregiving. When caring for someone with dementia, caregivers should try to de-emphasize the types of memories that are impaired, and try to exercise the person’s retained types of memories.
The term, risk factor or predisposing factor, refers to anything that increases the vulnerability for a condition. For example, obesity and a positive family history are risk factors for adult-onset or type II diabetes..
The known risk factors for memory problems associated with or without Alzheimer’s disease include family history, lower education level, older age, history of head trauma, illness, medications, including alcohol or illicit drugs, vision or hearing impairment, and uncontrolled chronic medical conditions, such as congestive heart or kidney failure.
Familial Alzheimer’s disease (FAD) or Early-onset Alzheimer’s affects less than 10% of those with Alzheimer’s disease and usually develops before age 65. If one parent has FAD, then the children have a 50/50 chance of developing it.
The majority of Alzheimer’s disease cases are late-onset, which usually develops after age 65. Late-onset Alzheimer’s disease has no known cause, however, genetic factors do appear to play a role in its development.
Several genes have been identified that appear to increase the risk for the disease, including a gene called Apolipoprotein E4 (or ApoE4). Another gene, ApoE2, appears to decrease the risk of developing the disease. At this time, there is no effective way to modify one’s genetic risk of developing Alzheimer’s disease.
Although the reason is not clearly understood, education level appears to influence the onset of Alzheimer’s disease. Some studies have shown that low education levels is related to an increased risk for Alzheimer’s, whereas higher education levels appear to have a protective effect against the disease. These studies suggest that learning and intellectual exercises can prevent or delay memory loss and the onset of Alzheimer’s disease.
Soon after the brain reaches maturity in a person’s 20s, it begins losing nerve cells (or neurons), though the loss is not noticeable until the 50s, or 60s. This loss of neurons causes a slowing of brain functioning, which accompanies an overall slowing of all body and physiologic processes, such as thinking, walking, and healing.
This generalized slowing of physical and mental processes due to aging has been addressed in terms of a noise model of signal detection. The noise model doesn’t refer to actual sound, but rather it refers to the random activity of brain cells. Information from our eyes and ears have to be processed against the background of this random brain activity, and anything that causes errors in this process is considered noise. Though noise is present at all ages, it seems to increase with age, contributing to less efficient and less accurate information processing and performance among the elderly.
Let’s discuss some of the specific aging factors that affect memory. These factors include physical changes to the body and brain, and psychological or social changes associated with aging.
Many medical conditions that become more common with aging can increase one’s risk of memory issues and Alzheimer’s disease. These include heart disease, strokes, high blood pressure, high cholesterol, diabetes, and hormonal imbalances. Many of these risk factors result in damage to blood vessels and reduce blood flow to the brain, which can result in brain damage and death. High blood sugar and insulin levels are also directly damaging to brain cells. Therefore, controlling these medical conditions is essential to reducing the risk of and memory impairment and Alzheimer’s disease.
Aging itself is associated with physical changes that can directly and indirectly affect memory. These include changes to the heart, blood vessels, lungs, kidneys, brain, and sensory systems. Aging results in a decline in the elasticity of the heart muscle and a thickening and hardening of the arteries, which can contribute to hypertension and inefficient circulation. Inefficient circulation can interfere with the essential blood supply to the brain, causing a weakening in brain functioning. This decrease in functioning can cause forgetfulness and confusion. A less efficient heart can also result in lowered endurance and greater fatigue, which can affect motivation and attention span, elements essential for learning and memory to occur.
In an equally direct way, changes in the lungs due to aging can severely affect thinking and memory. With aging, the lung’s capacity to exchange oxygen and carbon dioxide decreases. This can reduce the amount of oxygen to the brain, which can damage brain cells and reduce functioning. Additionally, reduced gas exchange can cause a back up of carbon dioxide in the brain, which can become toxic to brain cells.
Aging also causes a decline in the efficiency of the kidneys, which means that toxins and drugs may not get properly broken down and excreted from the body. Toxins can build up in the body and brain to hinder functioning and cause damage, which can be permanent. Because the brain is so vulnerable to toxins, confusion and forgetfulness may be the first signs of kidney problems. Poor bladder control may not affect memory per se, but preoccupation with it will affect attention and cause self-consciousness, which, in turn, can affect memory.
Physical Factors (Continued)
Psychological factors often associated with aging can also affect memory. Cautiousness, short attention span, loneliness and depression are a few of these. Decreased motivation stemming from lack of stimulation, lack of opportunity to use knowledge in everyday life and prejudices against the elderly contribute to the self-fulfilling prophecy of forgetfulness and confusion in the elderly person. This can result in low self-esteem and indifference to new information and practicing remaining skills.
In addition, old age is a time when people lose family and friends who have been part of their support systems, suffer losses in their mobility and other capacities. This can also erode confidence and self-esteem, resulting in an uneasy view of the physical and human environments.
Depression is the most frequently diagnosed mental illness in those over 65. One of the common complaints of depressed individuals is difficulty with memory. People with depression have difficulty with concentration. They are also preoccupied with concerns, which causes them to withdraw their attention from their environment. This inattention causes them to miss the clues that orient them to their environment. The combination of poor concentration and inattention can result in memory problems that can mimic dementia.
Depression can result from medical causes. Among the elderly, this can include medications and their side effects, chronic illness, such as heart and lung diseases that restrict blood circulation, and chronic pain, such as with arthritis.
Another reason that elders are susceptible to depression is that aging is associated with a decline in the body’s production of mood elevating substances. Older people also face changes in their body image, physical and mental abilities, careers, and the loss of loved ones. Often, the elderly are also socially isolated and lack the support system to help them deal with these changes. These factors can increase the risk of depression, which can lead to memory issues.
Anxiety and Stress
Anxiety and stress affect memory much in the same way as depression, by narrowing the perceptual field and decreasing concentration and attention span.
Though stress is a normal reaction to the many challenging experiences people face day to day, stress can become excessive or chronic and interfere with memory as well as cause serious health problems. Excessive or chronic stress or anxiety impacts the body, mind, and behavior.
Stress affects one’s values, attitudes and priorities about learning. Therefore managing stress and anxiety levels is critical for optimizing memory and mental functioning.
The brain’s health affects the entire body’s ability to function. If the brain is not able to function properly, it can impair language, understanding, memory, movement, immune function, and the sense of well-being. The brain is very sensitive to changes in its homeostasis. For example, infections in the brain or spinal column can cause delirium with hallucinations and delusions.
Any illness that causes pain, discomfort, or fever can cause concentration and memory issues. Aging is associated with many health issues that can cause chronic or severe pain, such as arthritis and compression fractures. Pain and discomfort can affect a person’s attitude and mental functioning.
A history of severe head trauma also increases the risk of memory problems and Alzheimer’s disease. This is likely due to the brain damage that often occurs with head injuries. Brain damage reduces the healthy brain reserve and results in earlier appearance of symptoms following further damage to the brain from aging or Alzheimer’s disease. In this case, prevention is the best approach to reducing this risk factor.
Any condition that compromises the ability of the brain to function properly can cause confusion and memory difficulties.
Another common cause of confusion and memory problems is drugs. The elderly use more medications than other age groups due to various conditions associated with aging. They also tend to use medications in combinations, increasing the possibility of adverse drug reactions.
The elderly are particularly susceptible to the adverse effects of drugs due to changes in the body associated with aging. All medications have side effects, and some can cause symptoms of dementia, such as confusion and memory issues. For example, many medications prescribed for depression, hyperactivity, schizophrenia, and other psychiatric illness can impair mental function.
Some people may experience memory problems and confusion while suffering withdrawal from a drug they have suddenly stopped taking. For example, a person dependent on alcohol or a prescription medication may suffer dementia-like symptoms when they stop drinking or miss a dose of the medication.
Now let’s discuss precipitating factors. A precipitating factor is an event or condition that elicits or contributes to the occurrence of a problem or to a critical decline of a condition. A woman with controlled diabetes, for example, may have her house burglarized and therefore feel stressed and eat erratically, precipitating a diabetic coma. Many unexpected and traumatic events can precipitate confusion and memory problems. We will discuss a few of these including physical trauma, personal or financial loss, dehydration, fluid retention, fecal impaction, fever and infection.
Physical trauma to any person can be very disorienting. The possible loss of blood, mobility, consciousness, and the loss of confidence that occurs when one’s expectations of safety and permanence have been violated can precipitate confusion and memory impairment. Even an elective surgical procedure is a traumatic experience with the unfamiliar environment, anesthesia, and cutting into the body. For example, confusion in elderly persons following hip fractures or surgical procedures is a common occurrence. The immobility, dependence, and loss of functional ability can be psychologically devastating as well as physically debilitating.
Personal or financial loss, such as the loss of a job can be very traumatic and result in memory difficulties. Many people are also traumatized when a loved one dies, and the grieving process can result in depression, lowered immune function, insomnia, and confusion in some individuals.
Dehydration and malnourishment can occur in older individuals with depression or a physical illness. Not only is the body depleted of essential fluids and nutrients, dehydration can cause toxins to build up in the blood and the brain, resulting in memory problems and confusion.
Precipitating Factors (Continued)
Other precipitating factors the can cause sudden confusion and memory problems include fluid retention and fecal impaction. Confusion can result from the stress of the retention, fluid and electrolyte imbalances, or a metabolic disturbance that affects the transportation of oxygen in the blood. Fluid retention and fecal impaction can occur more frequently among the elderly, especially those with dementia, and should always be considered when confusion occurs.
Mild Cognitive Impairment (MCI)
Mild cognitive impairment (MCI) is a term that refers to mental deficits that do not significantly interfere with a person’s functioning or daily life. MCI can include memory problems, slower thinking, and a reduced ability to learn. Individuals with MCI have forgetfulness beyond what one would expect for their age, but it is not severe enough to be called dementia.
Normal memory problems are generally associated with aging and are often characterized by such things as misplacing a book or car keys, forgetting someone’s name, or forgetting to pick up something at the store. In contrast, the memory loss that is associated with MCI is more severe and involves persistent problems in recalling important information. People with MCI may score poorly on memory tests, but this does not affect other aspects of their lives. Their memory and other functions may stay the same until death, though in some cases, the symptoms can worsen and develop into a dementia.
MCI appears to be a transitional state between normal memory and Alzheimer’s disease in some people. In a sense, MCI can be considered a risk factor for Alzheimer’s. Therefore preventing or treating MCI could be one approach to decreasing the risk of developing Alzheimer’s. Therefore MCI is being researched actively for treatments and preventive measures.
Alzheimer’s disease is just one of the diseases classified as an irreversible dementia. Though the specific cause may vary, irreversible dementia is associated with a massive loss of brain cells. This loss begins in specialized areas but eventually spreads to all regions of the brain. Irreversible dementias generally have a long, unremitting downhill course that ultimately results in death. Another class of dementias are called reversible dementias, because they can be can be reversed with treatment.
Reversible dementia can develop for several reasons including chronic medical conditions, such as heart disease and lung disease. When the heart is not working efficiently, such as in the case of congestive heart disease, the transport of oxygen and nutrients essential to brain function is limited. Chronic lung conditions such as emphysema or other form of chronic obstructive pulmonary disease, reduce the efficient exchange of oxygen and carbon dioxide in the lungs, causing carbon dioxide to buildup in the brain and reducing the supply of oxygen necessary for the brain to function properly.
Kidney and liver diseases can also cause reversible dementia. The kidneys and liver process and metabolize liquids, food, and medications. When these essential organs are diseased, they are unable to process the many toxins in the blood, which eventually cause damage to the brain.
Hormonal imbalances can cause confusion and abnormal behaviors as well as many other symptoms. For example, thyroid disease is relatively common cause of dementia among the elderly. Cushing’s disease, which causes and imbalance of hormones from the adrenal gland can also cause dementia.
Poor nutrition and vitamin deficiency can also cause reversible dementia. Brain cells require vitamins and minerals to maintain their health. The B vitamins, for example, are important in the maintenance of healthy nerves and blood cells. Folate, B6 & B12 deficiencies can contribute to cognitive decline and dementia.
Lastly, medications and substance abuse can impair mental function and cause reversible dementia. Unfortunately, as people age, they become more likely to develop adverse reactions from medications and drugs. Therefore it is important to carefully monitor medication and drug use, including alcohol.
Reversible Dementias (Continued)
It is critical that anyone showing signs of dementia, such as confusion, memory difficulties, and impaired function, be examined by a health care professional to determine the cause of the symptoms. Without a proper diagnosis and appropriate treatment, dementia that could have been improved or reversed may become irreversible with permanent brain damage.
It is important to avoid unnecessarily labeling a person with Alzheimer’s disease without a proper diagnosis. When individuals get labeled, others begin to interact with them differently. Labeled people can lose confidence and become more dependent, causing the symptoms to worsen and possibly lead to an irreversible dementia. It is also important to recognize that not all memory difficulties are due to Alzheimer’s disease or other form of dementia.
Why is forgetting perceived so negatively? In most societies, forgetfulness is associated with old age and poor mental functioning. The truth is that forgetfulness occurs at any age and under many different circumstances. And in reality, forgetting is not all bad. It would be distressing to remember every experience you ever. The ability to forget is an important function of the brain. But trying to control the degree of forgetfulness by controlling some of the risk factors for memory impairment may be a healthy goal.
In summary, memory formation and retrieval involve a complex process of relaying signals through a network of nerve cells and pathways. Information processing and storage require attention and concentration. The main types of memory are sensory, explicit, implicit, and spatial. Explicit memory includes episodic and semantic memories. Aging is associated with a decline in most forms of memory, particularly working memory, which is needed for information analysis and speech comprehension. Semantic and implicit memories remain largely intact with normal aging.
The risk factors for memory impairment include family history, lower education level, older age, history of head trauma, illness, medications, including alcohol or illicit drugs, vision or hearing impairment, uncontrolled chronic medical conditions, and psychological factors such as depression and stress.
Precipitating factors include physical trauma, personal or financial loss, dehydration, urinary or fecal retention, fever, and infection.
Mild cognitive impairment and reversible dementias can develop into irreversible dementia, such as Alzheimer’s disease.
Reversible dementias can be caused by many things including chronic medical conditions, vitamin deficiencies, and medications.
By controlling some of the known risk factors for memory impairment, it may be possible to prevent or limit memory loss.
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Written by: Catherine M. Harris, PhD, RNCS (University of New Mexico College of Nursing)
Edited by: Mindy J. Kim-Miller, MD, PhD (University of Chicago School of Medicine)
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