Neuropsychological Assessment Research Paper

1. Basic Concepts In Clinical Neuropsychology

The main areas of cognitive function which are affected by damage or dysfunction of brain structures are perception, orientation, motor abilities, attention, language, memory, and executive function, as well as affect and social behavior. Perception refers to the processing of stimuli and sensations from the external environment and the body. Perceptions involve the visual, audititory, tactile, and olfactory domains but most of our knowledge has derived from studies of the visual system. Visual perception is disrupted after lesions to the posterior regions of the brain, the occipital and temporal cortex. Specific lesions can disrupt the processing and perception of color, shape, or movement of objects, or lead to specific problems in recognizing faces or the meaning of objects.

With respect to complex motor abilities apraxia is an important concept. Apraxia refers to the inability to execute purposeful acts on verbal command and the inability to immitate gestures (Benton 1994).

Orientation refers to the specific awareness of a person in relation to time, place, situation and other people. Orientation requires intact attentional and perceptual abilities. Impairments of orientation are among the most frequent symptoms of brain disease (Lezak 1995). Transient loss of orientation is a common consequence of global disruption of brain function due to traumatic brain injury. Its duration depends upon the severity of the injury.

Attention is the ability to focus a ‘mental spotlight’ on sensory inputs, motor programs, memories, or internal representations (Kolb and Wishaw 1996), and also involves the capacity to concentrate on a task for a given period of time. Impairments in attentional functions are often observed as a result of diffuse brain damage (such as Alzheimer’s disease) and in a range of neuropsychiatric diseases such as schizophrenia or depression (Maruff and Pantelis 1999). Attentional problems are also seen in developmental disorders such as Attention Deficit Hyperactivity Disorder. A particularly striking form of an attentional deficit is contralateral neglect. Stimulus neglect is the failure to detect or to attend to stimuli in the visual space or body side contralateral to a parietal brain lesion in the absence of sensory deficits. In most cases neglect of the left side occurs after a right hemisphere lesion.

Another basic concept in neuropsychology is memory. Memory deficits are observed after traumatic brain injury, stroke, and in most neurodegenerative and neuropsychiatric diseases. There is general agreement that memory representation in the brain involves several subsystems, which are associated with different neuroanatomical structures. The most influential contemporary memory model is the ‘multiple memory systems approach’ proposed by Squire (1987). Declarative or explicit memory refers to information, which has been encoded in a specific spatiotemporal context (e.g., a name, face, or story) and can be assessed by conscious recollection. Semantic memory refers to knowledge about the world, whereas episodic memory mainly involves autobiographical information. Implicit or non-declarative memory refers to the influence of prior experience on behavior, even if such experiences are not remembered or cannot be ‘declared.’ Typical examples are the acquisition of motor and nonmotor skills or priming effects (Daum and Ackermann 1997). The brain area which mediates declarative memory formation is the hippocampus and related structures (Squire 1987). Non-declarative memory is dependent on a range of other areas, e.g., the basal ganglia and the neocortex (Daum and Ackermann 1997).

Another important concept of memory theories is working memory. Working memory is responsible for the integration of multiple stimuli, and the short-term maintenance of an active representation of information. Thus, working memory plays an important role in complex tasks such as learning, comprehension, and reasoning. There is general agreement about the fact that the prefrontal cortex mediates working memory functions (Fuster 1989). Working memory consists of two subsystems. One system is important for processing language and is called the phonological loop whereas the visuospatial sketch pad is important for processing visuospatial information. These two subsystems are controlled by an attentional control system, the central executive (Baddeley 1998).

Executive functions refer to supervisory abilities involved in the planning, initiation, maintenance, and adjustment of goaldirected behavior. They are activated whenever the routine selection of operations is insufficient and inappropriate. They are thus important for reasoning and problem-solving. The prefrontal cortex is critically involved in the supervision or execution of cognitive processes and is therefore involved in executive control (Mayes and Daum 1997). Disorders of language are frequently observed after damage to the left hemisphere of the brain. Two areas are of particular importance for language processing. One is Broca’s area and lies in the left frontal lobe. This region is essential for the expression of language whereas Wernicke’s area, which lies in the temporal lobe, is important for language comprehension. Impairments of verbal abilities, which are affected in the comprehension of language, are referred to as aphasia. Damage to Broca’s area leads to difficulties in language production with a milder impairment of comprehension. In Wernicke’s aphasia, the main symptom is a deficit in the comprehension of spoken language.

Changes in affect, personality and social behavior are also frequent sequelae of brain dysfunction. Emotional and personality changes can be the direct result of brain damage. Examples are apathy and loss of interests and initiative, but also loss of tact and inappropriate social behavior, which may occur after frontal lesions (Kolb and Wishaw 1996). Emotional problems may also result from insight in the cognitive problems, which occur after brain damage, and the resulting life changes. Emotional and personality changes are most frequently due to an interaction between brain damage and the reaction to disability.

2. Neuropsychological Standard Tests

The most common approach to clinical neuropsychological assessment is the use of standard test batteries such as the ‘Wechsler Adult Intelligence Scales’ (Lezak 1995) and the ‘Luria-Nebraska Neuropsychological Battery (see Lezak 1995). In this approach, the same tests are administered, irrespective of the specific lesion or disorder in an individual patient (Benton 1994). The use of such test batteries has several advantages e.g., normative reference data and the possibility to compare profiles across various neurologic conditions (Levin 1994). A more recent procedure involves the exploration of an individual’s clinical history, including detailed information about the site and extent of the lesion, or the severity of the disease and the administration of a series of specific tests. Individual problems and areas of preservation of cognitive function are assessed in relation to specific damage, which allows the development of an individual rehabilitation program.

2.1 Assessment Of Global Intellectual Functions

The most widely used test of general abilities is the ‘Wechsler Intelligence Scale’ (Wechsler 1987). The test includes six verbal tests and five performance tests. An overall IQ score is generally derived from these subtests. In addition, IQ scores can be derived separately from the verbal tests and the performance tests. Damage to the right hemisphere leads to a reduced performance IQ, whereas lesions to the left hemisphere tend to depress the verbal score.

2.2 Visuoperceptual Capacities

Perceptual tests primarily assess visuoperceptual and visuospatial abilities. Clinical investigations have shown that visual impairments are mainly associated with diseases and dysfunction of posterior regions of the right hemisphere.

Visual abilities are frequently assessed by tasks requiring the copy of line drawings. Examples are the complex figure or the ‘Benton Visual Retention Test’ (see Lezak 1995). Tests of shape, object, and visual space perception are assessed by the ‘Visual Object and Space Perception Test’ which includes e.g., the recognition of objects from silhouettes or the appreciation of the selective position of dots in a spatial arrangement (Warrington and James 1991).

A variety of tests have been developed for face recognition. The stimulus material is often comprised of familiar and unfamiliar faces. Face recognition is typically impaired in patients with damage of the right hemisphere. Tests, such as the ‘Florida Affect Battery,’ not only require basic processing of faces e.g., in face matching tasks, but also the recognition of emotional facial expressions (Bowers et al. 1992).

2.3 Attention

A common test for measuring attentional capacity is ‘Digit span,’ a subtest of the ‘Wechsler Intelligence Scale’. Random sequences of numbers are read aloud and have to be reproduced by the subject in forward or backward order. A visuo-spatial analogue is the ‘Corsi Block-tapping test’. In this test, the sequence of spatial positions of wooden cubes which are fixed on a board has to be reproduced. Frequently used concentration tests are ‘Digit Symbol’ a subtest from the ‘Wechsler Intelligence’ or ‘letter cancellation tests’. More recent tests have focused on the assessment of everyday attentional requirements, such as the ability to efficiently check phone books or maps. One of the most widely used ecologically valid instruments is the ‘Test of Everyday Attention’ by Robertson et al. (1996).

2.4 Memory

Memory profiles (e.g., differences in verbal or visual memory abilities, short-term, or long-term memory) are determined in batteries consisting of a range of different memory tests. A typical example is the ‘Wechsler Memory Scale’ (Wechsler 1987). Everyday memory abilities form the basis of the ‘Rivermead Memory Test’ (Wilson et al. 1985). Test demands are e.g., remembering a new route, a newspaper article, a hidden object, or an appointment.

An alternative approach to test batteries is to administer a range of different individual tests. To assess verbal memory, typically word lists, stories, or paired associates are presented, which have to be recalled or recognized immediately or after a delay interval of up to one hour (for a summary see Lezak 1995). Visual or spatial memory is assessed by the immediate and/or delayed recall of geometrical figures, spatial positions, or the recognition of visual patterns or faces.

2.5 Language

Tests of verbal abilities have been developed to tap the functional efficiency of the left hemisphere and to assess aphasia. One example is the vocabulary test, a subtest of the ‘Wechsler Intelligence Scale’, which assesses the ability to define common concepts. The ‘Token Test’ was developed to assess comprehension of spoken instructions. It measures the capability to carry out commands of varying complexity (e.g., ‘touch the blue square and the white square’). ‘Verbal Fluency’ is evaluated by the quantity of words that can be produced from a range of categories, e.g., names of countries or animals. Aphasic patients almost always perform badly. In addition, verbal fluency has been shown to be a sensitive indicator of left frontal lesions or neurodegenerative disease.

Brief screening instruments, such as the ‘Aphasia Screening Test’ and the ‘Multilingual Aphasia Examination’, allow an efficient assessment of aphasia (see Lezak 1995). The ‘Multilingual Aphasia Examination’ provides performance profiles concerning different aspects of language such as naming, repetition, verbal fluency, understanding, and spelling. Comprehensive instruments such as the ‘Boston Diagnostic Aphasia Examination’ (Goodglass and Kaplan 1983) assess a variety of specific aspects of language performance and allow the differential diagnosis of different aphasic syndromes.

2.6 Executive Functions

Frequently used tests of executive functions are the ‘Wisconsin Card Sorting Test,’ the ‘Stroop test’ (see Lezak 1995), and the recently developed ‘Hayling Test’ (Burgess and Shallice 1997). The ‘Wisconsin Card Sorting Test’ requires the detection of sorting rules (color, shape, and number of elements) and the modification of such rules in response to feedback. The ‘Stroop Test’ and the ‘Hayling Test’ assess the ability to suppress habitual responses. In the Stroop test, color words that are printed in a different color, have to be read aloud; the color of the written words has to be inhibited (e.g., the word ‘red’ printed in green). The Hayling Test requires the completion of sentences by unrelated words, obvious semantically related completions have to be suppressed. Further tests of executive function involve planning or problem solving within the context of complex puzzles such as the ‘Tower of London Task’ (see Lezak 1995).

2.7 Affect And Personality

Changes in personality or emotional processing play an important role in neuropsychological assessment, since they may affect performance on cognitive tests to a considerable degree. Depression in particular, is often observed after brain damage. The ‘Beck Depression Inventory’ assesses the degree and severity of depression and is frequently used in neuropsychological assessment (Beck 1987). The ‘Minnesota Multiphasic Inventory’ measures personality and emotional adjustment and is thought to be sensitive to affective disorders (Butcher et al. 1989) Minnesota Multiphasic Personality In entory (MMPI). Changes in social behavior and social interactions are inferred on relatives’ reports and behavioral observations in the testing situation.

3. Clinical Groups

Within the context of neuropsychological assessment, three main groups of clinical conditions can be differentiated. The first group includes people suffering from localized brain damage due to stroke, head trauma, or infections such as herpes simplex. Their cognitive problems vary and largely depend on the site and extent of the brain damage. The second group comprises people with neurological, mainly neurodegenerative diseases, such as Parkinson’s disease, Alzheimer’s disease, and multiple sclerosis (see Lezak 1995). In Parkinson’s disease the most frequently reported cognitive deficits are executive dysfunction, working memory deficits, and visuo-perceptual problems. Alzheimer’s disease is associated with episodic memory impairment, accompanied by language deficits, visual–spatial problems, and changes of personality. In multiple sclerosis the cognitive impairment affects a broad range of functions such as memory, learning, attention, concentration, reasoning, speed of information processing, and executive functions.

In recent research neuropsychological deficits have also been reported in psychiatric diseases, in particular in depression and schizophrenia. These findings make an important contribution to our understanding of the relation between cognitive impairments and psychiatric symptoms, and may help to identify predictors of the course of the illness (Keefe 1995). Neuropsychological impairments in schizophrenia comprise deficits in attention, executive functions, verbal memory, and learning (Keefe 1995). Attentional problems have been attributed to a failure in the selection of relevant from irrelevant emotions and cognitions.

In depression impairments of memory, executive functions, attention, and concentration have been reported. Therefore problems mainly occur on tasks which require effortful processing (Keefe 1995).

4. Specific Problems Of Neuropsychological Assessment

Neuropsychological tests are often very demanding and are dependent upon a high degree of compliance, motivation, and cooperation. They require the ability to understand and to follow instructions, and to concentrate for a considerable period of time. The potential influence of nervousness and test anxiety on cognitive performance also needs to be taken into account. The financial, emotional, and social advantages of illness and injuries may encourage malingering which poses a problem for neuropsychological assessment (Lezak 1995). Malingering individuals often show impairments that are greater than would be expected by chance or by a patient’s medical and social history. In addition, errors are made that are unrelated to the lesion or complaint. The analysis of inconsistencies with repeated testing may also contribute to the detection of malingering (Lezak 1995). Advances in functional imaging techniques and the combination of neuroimaging and neuropsychological assessment procedures will be of considerable help if psychological and organic aspects of cognitive dysfunction have to be distinguished.

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