Relationship between Clinical and Experimental Neuropsychology - Essay Example

Clinical and Experimental Neuropsychology Relationship between Clinical and Experimental Neuropsychology ____________________ Professor Name: ____________________ Dated: April 28, 2007-04-28 Any suspect of change in behaviour usually felt after brain damage or brain injury or any abnormality arising from brain disorder is called 'Clinical Neuropsychology' (CN) while experimental neuropsychology (EN) deals with the study of investigating human nervous system, thereby conducting laboratory assessment of human beings. The framework for component processes of neuropsychology demonstrates its application in three domains which are interdependent on one another: memory, spatial attention, and visual imagery. It is through these three domains that relationship between experimental and clinical perspectives can be integrated within a powerful and clarifying framework. (Maruish & Moses, 1997, p. 60) It can be said that EN deals with the proven methods of verifying CN with the help of conducting various tests and experiments not only on humans but also to some extent on animals. The relationship between clinical and experimental neuropsychology contains many aspects which are clear from the study of various psychosocial domains of brain diseases. In every cognitive domain there are aspects of language, visual perception, memory attention, and abstract reasoning, it is possible to find intriguing examples of dissociations within a specific cognitive function or otherwise curious distortions of the normal process. (Maruish & Moses, 1997, p. 59) The association between CN and EN can be depicted from those cases which are within any given cognitive function and are aware of the fact that a whole range of things can go wrong in not tested; conversely, a specific deficit in memory, attention, or language can manifest itself in a variety of interesting ways. The relationship highlights and bridges the gap between those particular disorders to its assessment. Intelligence Loss of intellectual power is a common consequence of brain disease. EN assessment of the patient with a degenerative neurological condition often incorporates the administration of an individual intelligence test. While Clinical measures make use of different scales to confirm the patient's intelligence. An example of the application of this procedure is the National Adult Reading Test (NART) (H. E. Nelson, 1982). Here the patient is asked to read aloud 50 words with irregular pronunciation (thyme, ache), in order to verify the test. The ability to pronounce words correctly is not lost until a late stage in dementia and underlying this procedure is the assumption that the number of pronunciation errors reflects past learning capability or intelligence. Memory and Amnesia It is quite difficult to make a clear distinction between psychological and neuropsychological approaches to memory. On one hand, many psychological concepts about memory have drawn on anecdotal observations of memory impairment in brain-damaged individuals, while, on the other, CN and EN psychologists have adopted many of the ideas about the structure and processes of memory from psychological investigations. If there is a difference in emphasis, it is that psychological research into memory function has tended to focus more on the structure and integrity of memory in 'normal' individuals, whereas the neuropsychological approach has concentrated primarily on the effects of brain damage or injury on memory function. Language Disturbances in language function are a frequent consequence of the 'dementing' process. Other language disorders include diseases like Aphasia which is commonly associated with the progression of Alzheimer's disease, but is also reported in patients with other degenerative conditions. Most comprehensive neuropsychological examinations of patients with dementing conditions involve some tests of the integrity of communication functions. Therefore it is clear that CN and EN are interlinked with each other through verification and proven tests. Now EN requires a variety of standardised procedures for the assessment of aphasia. Most of the aphasia tests comprise a collection of tasks designed to identify deficits in the patient's receptive and expressive language, nonverbal communication, reading, and writing. These are the different channels through which communications may be received, interpreted, and responded to, and are systematically evaluated using a variety of standardised clinical tests. The difficulty level of these tests is typically within the scope of most people with suspected or mild to moderate levels of dementia. (Knight, 1992, p. 40) Cognitive Functions Dementia in the context of CN is usually seen by clinicians as a global deterioration in intellectual and memory capacity. However, the neuropsychological assessment of patients with degenerative brain diseases typically involves testing a range of cognitive skills. EN requires various tests of spatial abilities, visuomotor impairments, and measures of frontal lobe functioning. EN requires many of the tests which are commonly employed to assess other cognitive functions and are encountered as the neuropsychological impairments seen in the various degenerative diseases. One exception, however, is the Wisconsin Card Sorting Test (WCST) which is possibly the most commonly employed measure of frontal lobe damage. The most common indicators of performance are the number of categories (or changes in rule) learned and the number of perservative errors. Perseveration is defined as the continued use of an old rule after a change to the new one has been made. Poor performance on the WCST has most commonly been attributed to frontal lobe damage (Lezak, 1983). Depression and Cognition The measurement of depression in elderly patients is the most frequent formal assessment of personal functioning undertaken by CN. Knowing something of a patient's current emotional status is often an important part of a neuropsychological assessment for a variety of reasons. First, depression may present as a reaction to the onset or progression of a chronic neurological condition and provide an indication of failure to adapt or cope. Such a reactive depression is treatable and the circumstances leading to its development need to be explored through EN. Depression has been particularly associated with Parkinson's disease, although it can occur in conjunction with many disorders. In addition, elderly patients may be so severely depressed that their cognition is impaired, and they be mistakenly diagnosed as having an organic dementia. Depressed patients often report severe cognitive deficits, which may be taken as a sign of dementia, however, in practice; many depressed elderly patients who consent to testing usually have scores on memory and intelligence tests in the normal range. (Knight, 1992, p. 44) That means there is no need of EN. In certain respects, however, the CN approach and methodology is quite distinct from that of cognitive neuropsychology. Whereas clinical neuropsychologists develop models that are anatomically referenced to specific cortical regions, cognitive neuropsychologists generate hypothetical models that more closely resemble flow diagrams. These serve as templates (hypotheses) that attempt to account for known cases of brain damage, but which must be amended if other cases come to light that do not fit. Cognitive neuropsychologists therefore put great weight on detailed case study of individuals with very specific brain damage, eschewing research based on groups of individuals on the grounds that brain damage is infinitely variable. Some researchers such as Caramazza (1984) also take issue with Fodor's assumption of localisation, pointing out that similar lesions do not always generate similar deficits. As a consequence, cognitive neuropsychological models may make no reference at all to possible underlying brain regions. (Stirling, 2002, p. 11) Visual Object Recognition Neuropsychology deals with the distinction between 'sensation' and 'perception' which sounds clear, but it is, to some extent, artificial, because a good deal of 'processing' of visual input takes place almost as soon as light enters the eye. In the retina, a network of cells interacts to provide the brain with evidence of contrast, colour and boundaries (edges). Retinal output, in the form of millions of nerve impulses, travels via the optic nerve and tract to the lateral geniculate nuclei (one on each side) of the thalamus. Here, information from the two eyes begins to coalesce, with input from the central fovic retinal regions being separated from peripheral retinal regions. Most lateral geniculate output is relayed on to the primary visual cortex where two vast 'sheets' of cells (in the left and right occipital lobes) map out the entire visual field. Cells in this region are arranged in columns and respond preferentially, and in some cases exclusively to particular types of visual input, such as the orientation of lines, whether the input conveys information about colour, or contrast, and so on. (Stirling, 2002, p. 155) Neuropsychologists tend to be more interested in the processes after sensory registration that leads to perception. In order to begin to understand these stages of processing, we need to look beyond V1 and V2 of the occipital lobe to other cortical regions that are implicated in the interpretation of visual sensation. There are separate cortical regions to deal with colour and movement, and additional regions to coordinate reading, object recognition and probably facial recognition too. In fact, visual areas seem to be scattered throughout the occipital, parietal and even temporal lobes. (Stirling, 2002, p. 155) There is substantial evidence that these areas divide (to some extent) into two separate processing streams, commonly referred to as the 'what' and 'where' streams (Ungerleider & Mishkin, 1982). Some brain disorders that seem to be anatomically and functionally linked to one or other stream are of interest in their own right, but they also provide clues about the sort of visual perceptual processing that must occur in 'intact' brains. Visual Perception In the mammalian brain, there is extensive output from the occipital lobes to other cortical regions that is carried primarily by two major fibre bundles. The inferior route follows a ventral course (round the side and particularly underneath) into the temporal lobes, whereas the superior route takes a dorsal course (over the top) into the posterior regions of the parietal lobes. EN has helped many researchers to suggest and prove by conducting laboratory research. In 1982, Ungerleider and Mishkin suggested that these anatomically distinct routes could also be distinguished in terms of the types of 'processing' they mediated. On the basis of data gleaned largely from lesion studies and electrical recording in monkeys, they proposed that the ventral stream is specialised for object recognition and perception, whereas the dorsal stream is specialised for spatial perception - i.e. for determining the locations of objects and their positions relative to one another and to the viewer. (Ungerleider & Mishkin, 1982) In the mammalian brain, there is extensive output from the occipital lobes to other cortical regions that is carried primarily by two major fibre bundles. The inferior route follows a ventral course (round the side and particularly underneath) into the temporal lobes, whereas the superior route takes a dorsal course (over the top) into the posterior regions of the parietal lobes. Ungerleider and Mishkin also suggested that these anatomically distinct routes could be distinguished in terms of the types of 'processing' they mediated. On the basis of data gleaned largely from lesion studies and electrical recording in monkeys, they proposed that the ventral stream is specialised for object recognition and perception, whereas the dorsal stream is specialised for spatial perception - i.e. for determining the locations of objects and their positions relative to one another. (Stirling, 2002, p. 155) Although Ungerleider and Mishkin's model was initially well received, but EN enabled the model to undergo both anatomical and conceptual revision as more has been learned about cortical regions involved in visual perception. Anatomically, it is certain that more cortical modules (i.e. functionally and anatomically distinct localised cortical regions, of which more than 30 have now been identified) are involved in the two streams than was initially thought. Moreover, modules within the two streams appear to interact with one another (i.e. send and receive projections) rather more extensively than Ungerleider and Mishkin anticipated. Finally, there is growing evidence that a third pathway, projecting into the superior temporal sulcus area (STS) is involved. The role of this stream is unclear, but the neurons in the STS that it projects to are poly-sensory, meaning that they respond to inputs from multiple sensory channels. It is therefore likely that this route is important in the integration of perceptual information about stimuli arising from different sensory inputs, such as appearance and touch. (Boussaoud, Ungerleider, & Desimone, 1990). The emergence of Cognitive Neuropsychology Approach It is through the combination of CN and EN that has made the cognitive neuropsychology approach successful by careful observation and neuropsychological testing, it is possible to distinguish between subtly different forms of language dysfunction. The neuro-imaging approach has not only tended to reinforce, but also to extend, classic models of how the brain processes language. In this approach, which is exemplified in the work of Caplan (1992) and Ellis and Young (1996), researchers try to understand the true nature of language disturbances in relation to underlying cognitive dysfunctions. Although this approach has evolved from the psycholinguistic approach reviewed earlier, it differs in two important respects. First, it tries to relate language and cognitive processes, and, secondly, it focuses on pathologies of language rather than normal language. (Ellis & Young, 1996) Because cognitive neuropsychologists focus on specific language impairments, syndromal (multi-faceted) conditions like Broca's and Wernicke's aphasia are of little direct interest. Indeed, although researchers are divided on the matter, some, at least, argue that studying groups of people with Broca's or Wernicke's aphasia is pointless because the conditions are both broad and poorly defined. Ellis and Young (1996) argue that as brain damage is inherently variable, potentially informative individual differences are lost in 'group' based research (Caramazza, 1984), so it makes more sense to conduct detailed case study investigations on individuals with very specific language impairments. Dronkers' approach in EN has shown that it is possible to draw conclusions about brain-language relations if one has access to aphasic individuals with carefully characterised symptoms/features and anatomically accurate information about brain lesions. The work of her group indicates that in addition to Broca's and Wernicke's areas and the arcuate fasciculus, many other regions, mainly on the left in the temporal lobe, contribute to both receptive and expressive language functions. Like Levelt, Dronkers et al. (2000) acknowledge that the neuropsychology of language has, for too long, been guided by an oversimplified model of how the brain deals with language. The emerging model must integrate the new language areas with the traditional ones, but also factor in attentional, executive and working memory processes in order to provide a more realistic framework of brain-language networks. (Dronkers, 2000) There are two modes of access for the development of the concept of attention and its functions. The first mode of access is through experimental research, where specific concepts are often based on circumscribed paradigms. Another mode of access is made possible by neuropsychological research: here the development of a differentiated concept of attention is usually based on the analysis of deficit patterns in individual cases of pathology. The results of experimental research and the neuropsychological analyses do not automatically lead to an identical perspective. Experimental concepts, which are usually based on specific paradigms, are in general operationally and thus unequivocally defined. However, the neuropsychological analyses of deficit patterns are limited because the deficits are intertwined with other intact or impaired cognitive processes, and because of the functional complexity of the diagnostic tools that are used. But we have to admit that the concepts derived from experimental paradigms with normal subjects do not automatically have a functional neuropsychological parallel. In other words, they are not always sufficient to explain specific deficit patterns observed in brain-injured patients. From a clinical perspective, attention processes are of central importance especially because of their significance for all other cognitive functions. Even more so, because according to findings to date, in addition to impairments in memory, impairments in attention are among the most common consequences of brain damage of very different kinds of etiologies. (Bohnen et al., 1995) However, the analysis of attentional performance plays a key role in psychological research in general and in neuropsychology in particular. The problem has been approached from different directions: purely experimental research in normal functioning, neurophysiological and neuroanatomical studies in animals and humans, neuropsychological studies of brain-injured subjects and, recently, through investigations of attentional processes using neuroimaging techniques. The various research approaches have led to an increasingly fine-meshed view of attentional performance, and in the process the number of different aspects of attentional performance has became quite large. For example, the following aspects have been discussed: focused attention, selective attention, control, vigilance, sustained attention, concentration, arousal, alertness, divided attention, capacity, effort, alternating attention, attentional shift, flexibility, lapses of attention, fatigability, inhibition, supervisory control, and speed of information processing. None the less, as of yet, there is no generally accepted consensus about the classification of specific attentional functions. Of course, the consistent use of these concepts in neuropsychology would be desired; however we are still far from such a standardised usage. This is surely less an expression of a lack of agreement and more likely the consequence of the fact that, despite all the intensive efforts deployed, until now we have not yet fully understood the phenomena underlying what we call attention. This is not only a theoretical problem but also a clinical one, because it raises questions as to which impairments in sub processes we can expect in patients with brain damage or brain disease, what diagnostic tools we should use, and which treatment of specific deficits in attentional performance we should take into account. (Leclerq & Zimmermann, 2002, p. 61) In a clinical context, a screening examination should be brief and sensitive to disorders secondary to a cerebral lesion, whereas, in a rehabilitation setting, the assessment should be large and exhaustive, with verbal or auditory and visual stimuli, in order to determine all relevant areas of weakness and strength. For general screening, when the goal is to identify persons with general neuropsychological disorders, a sensitive test such as SDMT should be selected. However, this test is not very specific, and so is of little value to the examiner hoping to delineate a specific attention disorder. (Leclerq & Zimmermann, 2002, p. 200) In EN the tasks are designed for the specific domain of research. Since the paper-and-pencil tests are so universally used, they could also provide further application as a baseline assessment in order to define inclusion or exclusion criteria. Neuropsychological Assessment in the light of Strengths and Weaknesses The neuropsychological approach relies on the use of tests in which poor performance may indicate either focal (localised) or diffuse (widespread) brain damage. Whether CN or EN, neuropsychological assessment serves several purposes. First, it can give a 'neuro-cognitive' profile of an individual, identifying both strengths and weaknesses. For example, an individual's initial assessment may highlight a specific problem with spatial memory set against a background of above average IQ. Since many tests are 'standardised', a person's performance can be readily compared with scores generated by other age or sex matched respondents (a process known as norm referencing). This can be referred to CN. A second advantage is that repeated testing over time can give an insight into changes in cognitive functioning that may relate either to recovery after accident/injury or the progression of a neurological illness. This can be categorised by EN. CN and EN Assessment Tests Usually, a series of tests (called a test battery) will be given. One widely used battery is the Halstead-Reitan, which includes measures of verbal and non-verbal intelligence, language, tactile and manipulative skills, auditory sensitivity, and so on (Reitan & Wolfson, 1993). Some of the tests are very straight-forward: The tapping test, which assesses motor function, requires nothing more than for the respondent to tap as quickly as possible with each of his/her fingers for a fixed time period on a touch sensitive pad. The Corsi block-tapping test measures spatial memory using a series of strategically placed wooden blocks on a tray. A third test measures memory span for sets of digits. The Luria-Nebraska test battery (Luria, 1966) is an even more exhaustive procedure taking about two to three hours to administer, and including over 250 test items. Poor performance on one particular test may signal possible localised damage or dysfunction, while poor across-the-board performance may indicate generalised damage. For example, inability to recognise objects by touch (astereo-gnosis) may be a sign of damage to the parietal lobes. A poor verbal test score (compared with a normal non-verbal test score) may indicate generalised left hemisphere damage. The WAISR is particularly useful in this respect because the eleven component tests segregate into six verbal and five performance sub-tests, from which it is possible to derive separate verbal and non-verbal estimates of IQ. (Stirling, 2002, p. 25) Dissociations and Double Dissociations Neuropsychologists typically try to design studies that provide evidence of the differential performance of brain-damaged and control subjects because such studies can inform structure-function relationships just like the relationship between CN and EN. Consider the following example: The right frontal lobe is thought to be important for memorising designs. To test this hypothesis, a researcher assesses memory for designs (MemD) and memory for words (MemW) in a group of people with known right frontal damage and a second group of non brain-damaged controls. Hypothetical results at first glance seem to support the hypothesis because the right frontal subjects appear to be selectively impaired on the MemD condition. Many neuropsychological investigations employ this sort of design, and use the evidence of a (single) dissociation between groups in the MemD but not the MemW as support for the hypothesis. (Stirling, 2002, p. 25) Researchers interested in understanding relation between CN and EN considers brain function and its relations to psychological function on a wide range of investigative techniques. By introducing lesion and ablation, electrical stimulation and recording, and the structural and functional in-vivo imaging procedures, scientists have been successful in understanding relationship between CN and EN. Consideration is also given to the burgeoning use of neuropsychological testing. Researchers have moved rapidly from an era in which analysis of brain structure could usually only be assessed after the person had died to an era in which the various in-vivo imaging techniques are quickly becoming almost as commonplace as X-radiography: their use in combination with neuropsychological procedures is a particularly promising research area. (Stirling, 2002, p. 29) References Bohnen, N.I., Jolles, J., Twijnstra, A., Mellink, R. and Wijnen, G. (1995). Late neurobehavioral symptoms after mild head injury. Brain Injury, 9, 27-33 Boussaoud, D., Ungerleider, L.G., & Desimone, R. (1990). Pathways for motion analysis: cortical connections of the medial superior temporal and fundus of the superior temporal visual areas in the macaque. Journal of Comparative Neurology, 296, 462-495. Caramazza, A. (1984). The logic of neuropsychological research and the problem of patient classification in aphasia. Brain and Language, 21, 9-20 Dronkers, N.F., Redfern, B.B., & Knight, R.T. (2000). 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E. (1982). The National Adult Reading Test. Windsor, England: NFERNelson Reitan, R.M., & Wolfson, D. (1993). The Halstead-Reitan Neuropsychological test battery: Theory and clinical interpretation. Tucson AZ: Neuropsychology Press Stirling John, (2002) Introducing Neuropsychology: Psychology Press: New York. Ungerleider, L.G., & Mishkin, M. (1982). Two cortical visual systems. In D.J. Ingle, M.A. Goodale and R.J.W. Mansfield (Eds.), Analysis of visual behaviour (pp. 549-586). Cambridge, MA: MIT Press Read More