About Memory & Dementia

Introduction

As we get older our memory and thinking processes (referred to as cognition) can change with age. For instance, we may occasionally forget where we left our car keys or reading glasses, or from time to time, we may forget an appointment or accidently miss a utility bill payment.  In many cases, these changes do not affect our ability to function normally in everyday life and are simply a mild annoyance which is part and parcel of normal ageing. However, in some cases memory changes can be more pronounced – for instance, an individual may be unable to remember the names of family members or friends, may forget how to prepare everyday meals, or may get lost on route to the local shops and be unable to find their way home.  In these cases the memory problems directly affect the individual’s ability to function in day-to-day life and may suggest the presence of a pathological process such as dementia.  Distinguishing between memory changes caused by normal ageing and those caused by dementia can be challenging; at the RICE centre we have an extensive research programme exploring new techniques for diagnosing and treating dementia. We also run a series of memory clinics to help identify and diagnose individuals with dementia and these clinics are directly informed by the research work carried out at the institute. In the sections below we explore what dementia is and look at the different types of dementia which we see in our clinic regularly.

What is Dementia?

Dementia is the label for a group of progressive (slowly worsening) neurological conditions which significantly affect cognitive abilities (i.e., memory, thinking, language, planning and perception) as well as activities of daily living. Alzheimer’s disease is the most common form of this disorder; however there are over one hundred different varieties of dementia. Individuals over the age of 65 tend be the most likely to be effected by dementia, however some forms of this condition are more likely to be present in individuals below the age of 65 (e.g., see Frontotemporal Dementia below).

Mild Cognitive Impairment

Before discussing the different forms of dementia in greater depth it is very important to highlight that not everyone who has difficulties with their memory will have dementia. The term Mild Cognitive Impairment (or MCI) is used to describe a condition where an individual has subtle, but detectable, problems with memory or other thinking processes but are generally able to function normally in everyday life (i.e., they can prepare meals, manage their finances and maintain familial/social relationships). Assessments carried out in the clinic reveal problems with memory which are slightly greater than would be expected for the individual’s age and educational background however, these problems are not at the level that would be characteristic of dementia.  Often these changes will be quite isolated, for example, only affecting memory but not other thinking processes such as attention or language.  In many cases these mild cognitive changes can result from other treatable conditions such anxiety, depression, stress or other physical illnesses, and not from any specific neurological problem. However, for some people MCI can represent the very earliest stages of Alzheimer’s disease or some other form of dementia.

Alzheimer’s Disease

Approximately half a million people in the United Kingdom currently have a diagnosis of Alzheimer’s disease, making this condition the most common form of dementia. This condition is most frequently seen in individuals over the age of 65 and is more likely to develop with increasing age. Alzheimer’s disease is caused by a specific set of brain changes – the development of amyloid plaques and tau tangles – which disrupt the ability of brain cells to process information. Initially, plaques and tangles tend to form in the areas of the brain which are responsible for memory formation (the hippocampus and medial temporal lobes), but as the dementia progresses they start to spread to other brain regions leading to additional problems with thinking, reasoning and language. The most common cognitive symptom of early-stage Alzheimer’s disease is memory dysfunction; an individual may find it difficult to remember recently experienced information. For example, after a short delay of a couple of minutes an individual may be unable to remember the details of a conversation they have just had. In addition, individuals with Alzheimer’s disease often have problems planning and organising their activities, processing visuospatial information in their environment and recognising family and friends, particularly in the later stages.   

Less commonly the brain changes associated with Alzheimer’s disease (i.e., plaques and tangles) affect areas of the brain responsible for language or visuospatial processing, but leave the regions responsible for memory relatively spared. Two examples of this form of Alzheimer’s disease are: (1) PCA – Posterior Cortical Atrophy, which typically affects the ability to process visual and spatial information and; (2) LPA – Logopenic Progressive Aphasia, which typically causes problems with speech production and language processing. Both of these conditions are far less common than the typical “memory-impaired” form of Alzheimer’s disease.   

Vascular Dementia

Vascular dementia is the second most common form of dementia in the United Kingdom, and accounts for roughly 20% of all cases of dementia. For the human brain to function effectively it requires a consistent supply of oxygen-rich blood, which it receives through a network of blood vessels called the vascular system. In Vascular dementia the blood vessels in the brain become damaged resulting in reduced blood supply to certain parts of the brain. In this condition, changes to the vascular system are usually caused by either a series of very small strokes, or a condition called small vessel disease which damages the tiny blood vessels in the centre of the brain.  Because of the way these vascular changes develop (often quite suddenly), the progression of vascular dementia is different from many other forms of dementia such as Alzheimer’s disease; cognitive decline often occurs in a step-wise pattern with periods of stable functioning followed by a sudden drop in performance which then stabilises to a lower overall level of functioning.  Common symptoms of Vascular dementia include difficulties with concentration and communication, memory dysfunction (although often not to the extent seen in Alzheimer’s disease), symptoms of stroke such as physical weakness or paralysis, periods of acute confusion, and depression. In some people, vascular changes occur alongside Alzheimer’s disease pathology, causing a mixed-form of dementia which shares features of the two primary disorders. This condition tends to me more common in older individuals.

Lewy Body Dementia  

Lewy Body dementia accounts for approximately 10% of all diagnosed cases of dementia in the UK. The disorder tends to be most prevalent in individuals over the age of 65; however it can occur in younger people as well, although this is less common. The condition is caused by the development of Lewy Bodies which are abnormal deposits of protein which form inside nerve cells in the brain.  Lewy Bodies disrupt the communication of nerve cells by interfering with chemical messengers (neurotransmitters) such as acetylcholine and dopamine.  Individuals with Lewy body dementia will often experience vivid visual hallucinations such as seeing animals or people which are not actually present. Periods of fluctuation in performance are also a common characteristic of Lewy Body dementia; tasks which are performed well one day, or at one point in the day, may be performed more poorly the next day, or a few hours later in the same day. Sleep disturbance is often present in this condition; individuals with Lewy Body dementia may experience vivid dreams and night-time restlessness, accompanied by a tendency to fall asleep in the daytime.  Lewy Body dementia shares characteristics of both Parkinson’s disease and Alzheimer’s disease. Individuals may have some of the motor symptoms which are typical of Parkinson’s disease such as muscle stiffness, trembling of the limbs, a tendency to shuffle when walking, loss of facial expression, and changes in the strength and tone of the voice. Like individuals with Alzheimer’s disease, individuals with Lewy body dementia frequently have problems with spatial orientation (i.e., knowing where they are, and navigating in their environment) and memory, although the degree of memory dysfunction is not normally as pronounced. Problems with visuospatial processing and executive functions (i.e., planning and coordinating mentally activities) are prominent features of Lewy Body Dementia. 

Frontotemporal Dementia

Frontotemporal Dementia is relatively rare, accounting for less than 2% of all cases of dementia in the United Kingdom. Unlike Alzheimer’s disease, which becomes more likely with increasing age, Frontotemporal dementia is less common in individuals over the age of 65, and tends to predominantly affect adults between the age of 45 and 65. Even though Frontotemporal dementia is relatively rare, it is the second most common form of dementia in younger adults (Alzheimer’s Disease is the most common).  A number of different changes have been identified in the brains of individuals with Frontotemporal dementia, including the formation of Pick Cells (abnormal deposits of protein which affect the function of brain cells) and cellular changes similar to those seen in Motor Neurone disease. Frontotemporal dementia receives its name from the regions of the brain that are most commonly affected in the condition. Brain degeneration tends to affect the frontal lobes of the brain – which support speaking, planning and controlling behaviour – and the temporal lobes which are responsible for comprehending speech, storing factual information about the world, and memory. Currently three different forms of Frontotemporal dementia are recognised, each of which have quite different clinical presentations, these are: (1) behavioural-variant Frontotemporal dementia; (2) progressive non-fluent aphasia and; (3) semantic dementia.    

(1) Behavioural-variant Frontotemporal dementia (bvFTD) is characterised by personality changes and behavioural disturbances. Some of the most common symptoms include a of loss inhibition (saying or doing things which are socially inappropriate), reduced empathy (problems understanding and responding to the needs of others), problems with planning and organising activities, increased distractibility, changes in food preference (a propensity to eat large quantities of sweet food) and a tendency to develop compulsive rituals (e.g. watching the same movie repeatedly). 

(2) Progressive non-fluent aphasia (PNFA) is characterised by problems with speech production. Individuals may struggle to find the correct words when engaging in conversation. Often individuals will struggle to pronounce words correctly (especially if they have more than two syllables), and their speech will lack appropriate grammar. Problems understanding speech can also be present, especially if the sentence contains complex grammar.

(3) Semantic dementia is characterised by a selective deficit of semantic memory, which is our memory store for factual information about the world around us – e.g., the knowledge that apples are fruit is a semantic memory.  Individuals affected by this condition have difficulty understanding the meaning of written and spoken language, pictures and objects.  In some cases of semantic dementia a mild form of the behavioural changes seen in behavioural-variant Frontotemporal dementia may develop as the condition progresses.



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