Dr Sebastian Crutch, Dementia Research Centre, UCL
Neuropsychology is the branch of psychology that deals with the relationship between the nervous system, especially the brain, and cerebral or mental functions such as language, memory, and perception. In other words, neuropsychologists are interested in how aspects of our behaviour and mental abilities alter following damage to or degeneration of the brain. By testing and measuring our behaviour and abilities, neuropsychologists try to make inferences about the nature, extent and location of the underlying brain cell loss or dysfunction. In this article, we look at the role which neuropsychologists can play in the diagnosis of FTLD and other degenerative conditions. We also explore the motivation for the questions which neuropsychologists ask, and in particular consider the characteristic symptoms associated with damage to different parts of the brain.
The role of the neuropsychologist
When someone presents to their doctor with concerns about their behaviour or mental abilities, there are four main ways in which a neuropsychologist might be able to contribute to the diagnosis, care and support which that person receives.
First, neuropsychologists work to identify and corroborate cognitive problems (difficulties with memory, language and other higher brain functions). The patient, their family and other healthcare professionals may be well aware that the person has a problem with their memory for example, but a neuropsychologist tries to measure that deficit and to place it on a quantitative scale using standardised tests.
Second, they assess whether the person meets established diagnostic criteria for a particular degenerative disease. For example, some criteria for Alzheimer’s disease require a person to demonstrate evidence of impairments not only in memory but also in at least one other area such as language, perception or decision-making. Therefore it is important to assess not only the mental ability for which the person complains of difficulties, but also other skills in order to determine how focal or widespread the problem may be.
Third, particularly for patients with degenerative conditions, neuropsychologists attempt to measure change in cognitive abilities. Having detailed scores can be particularly important in the earliest stages of a disease, when the difficulties are relatively mild. It is sometimes not possible to determine from a single assessment whether someone’s performance on a test at or below the level they would have achieved prior to their illness. So two or more assessments are required in order to determine whether their scores on a particular test stay the same or improve (as might expected for a healthy individual) or decline (as might be expected for someone for a degenerative condition).
Fourth, neuropsychologists have a role to play in helping people with dementia and their families, friends and carers to better understand their difficulties. Sometimes understanding why and how certain problems or difficult behaviours occur can help the person with dementia or particularly those caring for them to accept and adapt to those problems better than when they remain unexplained. For example, people with Posterior Cortical Atrophy (PCA), a rare form of Alzheimer’s disease which affects the back of the brain causing problems with vision, might fail to pass something across the dinner table when asked, not because they are being deliberately unhelpful, but because they simply cannot perceive where the item they have been asked for is located. Similarly, someone with FTD might swear at a stranger in the street, not because they are being deliberately rude, but because the part of the brain which usually acts to inhibit such socially-unacceptable behaviour has been damaged.
Figure 1. The lobes of the brain and their specialised functions.
The specialisation of the brain
It would be a considerable understatement to say that the structure of the brain is complicated. However, by studying behaviour and cognitive abilities in people with both healthy and damaged brains, scientists have been able to determine the principle functions of different brain areas. We look here at how the four lobes of the brain (shown in Figure 1) contribute to our experience of the world, starting at the back of the brain with the occipital lobes.
The occipital lobes
Although the eyes are the source of visual information about the world around us, it is actually the brain which does most of the hard work. The eyes convert sensory information about light into electrical impulses, but these are passed to the brain for interpretation. The occipital lobes are particularly important in the processing of form, colour, motion and location, skills which underpin the brain’s ability to provide us with a complete 3D picture of the world. Therefore, the processing carried out by the occipital lobes enables the brain to perceive the identity of objects (e.g. faces, cars, animals) and to determine their location (e.g. on the left; far ahead). Tests for occipital lobe function include detecting or discriminating shapes and colours, and detecting patterns of coherent movement among arrays of moving dots. Poor performance on tests sensitive to occipital lobe function are common in Alzheimer’s disease but rare in FTLD.
The parietal lobes
The functions of the parietal lobe are somewhat more diverse, and there is a significant difference between the dominant side (the left in most people) and the non-dominant side. The dominant parietal lobe can be thought of as being concerned with things we have to put together into an order or structure. So tasks such as writing and spelling (which require putting letters and words together) and calculation (which involves ordering and combining numbers) are critically dependent on the dominant parietal lobe. This side of the parietal lobe has also been heavily implicated in a condition known as apraxia, an impairment of learned purposive movements, which is tested for by asking people to imitate or pantomime gestures and movements. The non-dominant parietal lobe could be thought of as our '3D centre'. One function of this area is to combine visual information from the occipital lobes into a 3D representation of the object being viewed. Damage to this area leads to a symptom known as visual agnosia, an inability to recognise objects, faces or surroundings. This is the reason the neuropsychologists often ask people to try to identify pictures and degraded or distorted images. The parietal lobes also contribute to our understanding of space, both in terms of our sense of body and personal space (e.g. knowing where our hand is relative to our body), and in terms of calculating the location of objects in external space (e.g. when we are reaching to pick something up). Spatial skills are often tested by asking people to count dots, arrange blocks in a particular order or to perceive which of two squares has a dot exactly in the centre.
Figure 2. Example tests of parietal function.
The temporal lobes
The temporal lobes deal primarily with memory and language functions. Neuropsychologists test for the status of at least two types of memory. Episodic memory which, as its name suggests, is our memory of events or episodes which are recorded with a reference to the time when they occurred (for example: 'I ate eggs for breakfast this morning'). Tests for episodic memory include asking someone to remember as many words as they can from a word list read aloud, or showing someone a series of photos of unfamiliar faces and then asking them to identify those same faces from among a larger sample. By contrast, semantic memory can be thought of as our encyclopaedia for facts and figures about the world (for example: 'Eggs have a shell, are laid by hens, and can be eaten boiled, scrambled or fried'). Episodic memory is compromised to some extent in most forms of dementia but perhaps most profoundly in Alzheimer’s disease. Semantic memory is most selectively and seriously affected in individuals with semantic dementia.
The frontal lobes
The frontal lobes perform multiple different functions yet work in unison to form our executive or management centre. The lateral or outer surfaces of the frontal lobe appear to be critical for organising and planning our actions and learning new tasks. In learning to drive, for example, these brain areas help us put together a very complex sequence of movements, which at first seem difficult and clumsy but gradually become more smooth and automatic. For someone with damage to this area, it is like being a learner all over again with many multi-stage tasks such as cooking and shopping becoming very difficult because the pattern or plan of action has been lost. Damage to these lateral areas can also cause people to get stuck on what they are doing (known as 'perseveration'). The middle portion of the frontal lobe generates our motivation and general impetus. If this part of the brain is affected, people can lose their 'get-up-and-go', becoming lethargic and reluctant to get out of bed or perform a particular activity. Again, it is important to realise that what might be perceived as laziness by some could be a direct consequence of the loss of cells in this area of the brain. The regulation of our behaviour appears to be governed by a third area of the frontal lobes, the orbitobasal area, located in the curvature at the very front of the brain. In healthy people these parts of the brain help to monitor, control and moderate our behaviour: for example, preventing us from saying something rude when someone has really annoyed us. Neuropsychologists probe the integrity of frontal lobe functions with a range of tasks which require attention, decision-making, persistence and inhibition. These include sorting items into categories (e.g. colours and shapes), alternating rapidly between two tasks (e.g. finding numbers and letters), and suppressing pre-potent responses (e.g. naming the colour of the ink a word is printed in rather than reading the word itself). These tasks eventually become difficult for most people with a progressive degenerative condition, but are particularly affected in FTD in the early stages of the disease.
Challenges facing neuropsychologists
Unfortunately of course it’s not quite that simple. Although different parts of the brain are undoubtedly specialised for different tasks, the brain works as a network. Some parts are particularly important for individual skills, but most tests at the neuropsychologist’s disposal in fact require the person being tested to use more than one skill at a time. Take for instance picture naming, a common test used for assessing language abilities and in particular word retrieval skills. In showing someone a picture of a dog and asking them to name it, the neuropsychologist is in fact requiring the person to perceive the picture clearly (its shape, colour, features, etc.), know what it is (i.e. access correct semantic knowledge about dogs), retrieve the correct name, and then to say the name aloud (requiring appropriate pronunciation and coordination of speech muscles to create the correct sound). So many stages underlying such an apparently simple task.
This is one of the reasons why neuropsychologists often ask a lot of questions; they need to assess as many different skills as possible in order to derive the most accurate cognitive profile of the person being tested. Numerous other factors also have to be taken into account, such as the previous abilities of the person being tested, their education, age, mood, tiredness, how long they have had the disease for, whether they have tried the test before, and also how difficult the test is for other people of a similar age and background.
Overall neuropsychology offers a non-invasive window into the brain, providing information which, in coordination with clinical interviews, brain scans and blood tests, can help health professionals to reach a prompt and accurate diagnosis. At its best, neuropsychological assessments can also be used to inform patients and carers about the condition they are facing, and to guide coping strategies and care planning.
Fundamentally, neuropsychologists should be asking questions which increase understanding of how and why challenging behaviours occur, and thus enable carers in particular to focus more upon the person with dementia than the dementia itself. Or, as the Canadian physician William Osler (1849-1919) put it, “Ask not what disease the person has, but rather what person the disease has.”