Memory Disorders

The study of memory loss in people with amnesia has created much of the knowledge of memory we know today. Besides amnesia, there are many other memory disorders, nearly all of which are caused by damage or injury to parts of the brain involved in memory processing.

 Agnosia

Agnosia is failure to recognize certain objects, persons or sounds. Familiar objects lose their relevance. Sometimes the geometric features of a face or object can be perceived, but the person does not know what the object is used for or if the face is familiar or not. Hearing or vision can be exclusively affected. Agnosia is usually caused by damage to the brain from neurological disorder (commonly in the occipital or parietal lobes), strokes, dementia or neurological disorders. Types of agnosia include visual, auditory, prosopagnosia, somatosensory and simultanagosia. Agnosia can disturb routine activities and affect overall quality of life. Although there is no direct cure, occupational or speech therapy can sometimes improve the condition. Underlying diseases should be identified so they can be corrected.

 Amnesia

Also called amnestic syndrome, amnesia is a condition where one’s memory is lost or disturbed. Amnesia is an oft-used plot device in novels and films, where the victim forgets who he or she is. Real-life amnesia is usually not so dramatic, and self-identity is often preserved. People with amnesia find it hard to form new memories and learn new information. Memories are scattered all over the brain, and damage to any area of the brain involved in memory processing can cause amnesia. Injury to structures of the limbic system (which controls memory and emotions) including the thalamus and the hippocampal formations affect memory processing.

Amnesia caused by brain injury is called organic or neurological amnesia. Some causes include brain inflammation (encephalitis) from infection or reaction to cancer, brain tumors in the areas that control memory, stroke, degenerative brain disorders like Alzheimer’s or dementia, alcohol abuse and lack of oxygen in the brain from heart attack or carbon monoxide poisoning. A type of amnesia called psychogenic or dissociative amnesia is caused by severe emotional trauma (for example, victims of violence), leading to the usually brief loss of personal information and memories. Scientists are investigating neurotransmitters involved in memory processing, but the complexity of the brain make it unlikely that any one drug can solve all memory problems. Currently, no drugs exist to treat most types of amnestic syndrome. Occupational therapy can help the patient learn new information and provide memory training. Mobile devices also help patients to remind them of tasks like taking medications on time.

Alzheimer’s Disease

The most common form of dementia is incurable and degenerative. The disease is progressive, growing from mild to worse. There is substantial loss of neurons, causing a

decline in memory functions and intellectual and social skills. Age is the greatest risk factor for Alzheimer’s, followed by family history, sex (women are more likely to suffer because they live longer) and lifestyle factors. Alzheimer’s is usually diagnosed in people over 65 years of age, but it can occur earlier (early-onset Alzheimer’s). Common symptoms include the inability to acquire new memories and the difficulty in recalling recent events. The brains of Alzheimer’s victims show plaques and tangles. Plaques are protein clumps that kill cells by interfering with cell communication, among other things. Tangles are twisted tau proteins that interfere with the transport of nutrients to cells, causing the cells to die. Drugs cannot cure Alzheimer’s, but they can treat memory symptoms by boosting cell to cell communication.

Dementia

Dementia is not a disease but a group of symptoms characterized by loss of cognitive ability beyond that caused by normal aging. Dementia occurring before the age of 65 is known as early-onset dementia. Dementia can be the result of brain injury, bodily damage or disease. Alzheimer’s disease is the most common cause of progressive dementia in people age 65 and older. Vascular dementia is the second most common type of dementia, where there is a problem with arteries supplying the brain and heart. This can be caused by high blood pressure, stroke, infection and amyloid protein build-up in the blood vessels of the brain. Lewy body dementia is characterized by the presence of abnormal protein clumps in the brain. Frontotemporal dementia is a less common type of dementia where nerve cells in the frontal and temporal lobes (areas associated with personality and behavior) of the brain degenerate. One form of frontotemporal dementia is Pick’s disease, where tangles of tau protein form in the brain. Other disorders linked to dementia are Huntington’s disease, dementia pugilistica (also called boxer’s dementia, caused by repetitive trauma to the head), Creutzfeldt-Jakob disease, and HIV-related dementia. No standard treatment exists for dementia, but certain drugs can slow or sometimes halt its progress.

 Huntington’s Disease

Huntington’s is an inherited disease that causes the progressive breakdown of nerve cells in the brain. Short term and long term memory are also affected, including episodic, procedural and working memories. Huntington’s is caused by an inherited defect in one gene. A person has a 50 percent chance of inheriting the disease if one of his or her parents has the disease. There is no drug that can cure Huntington’s or alter its course, but medications can improve motor and psychiatric symptoms.

Wernicke-Korsakoff’s Syndrome

Also called wet brain, this is a combination of Wernicke’s encephalopathy and Korsakoff’s amnesic syndrome. Both are generally considered different stages of the same disorder; Wernicke’s is the acute phase and Korsakoff’s is the chronic phase. The syndrome often

causes changes in vision, loss of muscle coordination and impaired memory. Thiamine (vitamin B1) deficiency related to alcohol abuse and/or food malabsorption is the primary cause. Korsakoff psychosis often develop as Wernicke’s symptoms fade. Other causes are AIDS, heart failure, long-term dialysis, very high thyroid levels, malignant cancers and extreme vomiting in pregnant women. Drugs can control symptoms and can prevent the disorder from getting worse, but loss of memory and thinking skills may be permanent.

Parkinson’s Disease

Parkinson’s is a progressive nervous system disorder that affects movement and belongs to the group of motor system disorders. Lack of dopamine, lack of norepinephrine and the presence of protein clumps called Lewy bodies are found in brains of people with Parkinson’s. There are four main disease symptoms: tremor, stiffness of limbs, slow movements and impaired balance. Other symptoms can include depression, mood changes, sleep disruptions and others. The exact cause of Parkinson’s is unknown, but genes and environmental factors play a role. Genetic mutations and exposure to toxins and viruses may be triggers. Age is a major risk factor for the disease, which usually begins in middle or late life. Men are more likely to develop Parkinson’s rather than women.

Hyperthymestic Syndrome

Also known as hyperthymesia or piking syndrome, hyperthymestic syndrome is a condition where the affected individual has superior autobiographical memory. The person may spend large amounts of time thinking about their past or they may have an extraordinary ability to recall specific events from their past life.