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Biomedical subjects

R G Brown

Publications and source records attributed to R G Brown.

At least 73 records · Page 4Linked to original sources
PubMed1992

Effect of practice on performance of a skilled motor task in patients with Parkinson's disease.

Parkinson's disease leads to a breakdown in the execution of highly practised, skilled movements such as walking and handwriting. The improved execution of skilled movements with practice can be understood as a process of schema learning, the determining of the relevant parameters of the specific movement. The ability of patients with Parkinson's disease and age matched normal control subjects to improve their performance, with practice, on a skilled motor task, doing up buttons, was assessed. The task was assessed on its own and with simultaneous foot tapping. Both groups showed an initial improvement in the task on its own and deterioration in performance when buttoning with foot tapping. The amount of interference, however, decreased with practice, particularly in the patients with a 2 Hz tapping rate. The results suggest that patients with Parkinson's disease are capable of schema learning but require more practice than control subjects to achieve comparable levels of performance. This may be a reflection of the fundamental motor dysfunction of the disease rather than a specific learning deficit.

Adult↗
PubMed1992

Regional cerebral blood flow abnormalities in depressed patients with cognitive impairment.

Depression with cognitive impairment, so called depressive pseudodementia, is commonly mistaken for a neurodegenerative dementia. Using positron emission tomography (PET) derived measures of regional cerebral blood flow (rCBF) a cohort of 33 patients with major depression was studied. Ten patients displayed significant and reversible cognitive impairment. The patterns of rCBF of these patients were compared with a cohort of equally depressed non-cognitively impaired depressed patients. In the depressed cognitively impaired patients a profile of rCBF abnormalities was identified consisting of decreases in the left anterior medial prefrontal cortex and increases in the cerebellar vermis. These changes were additional to those seen in depression alone and are distinct from those described in neurodegenerative dementia. The cognitive impairment seen in a proportion of depressed patients would seem to be associated with dysfunction of neural systems distinct from those implicated in depression alone or the neurodegenerative dementias.

Bipolar Disorder↗
PubMed1991

Determining the cause of anemia. General approach, with emphasis on microcytic hypochromic anemias.

In the vast majority of cases, the cause of microcytic hypochromic anemia is clearly suggested by the patient history, physical examination results, red cell indexes, and peripheral blood smear. Thus, further diagnostic testing, if necessary, can be very selective. When the underlying cause of anemia is obscure, the serum ferritin concentration should be measured first. If it is normal or increased, serum iron and free erythrocyte protoporphyrin levels can be determined. The serum iron level is low in anemias caused by iron deficiency and chronic disease but normal or elevated in those resulting from the thalassemias, hemoglobin E disorders, and lead toxicity. The free erythrocyte protoporphyrin level is elevated with iron deficiency, the anemia of chronic disease, and lead toxicity but normal with thalassemias and hemoglobin E disorders. Results of these two test indicate which of the more specific tests is most likely to yield the correct diagnosis.

Adolescent↗
PubMed1991

Normocytic and macrocytic anemias.

Differential diagnosis of normocytic and macrocytic anemias is guided by the patient history, physical examination results, reticulocyte count, and specific red blood cell abnormalities identified on the peripheral smear. In some cases this information is sufficient for diagnosis. When further tests are needed, a stepwise approach, as described by the author, ensures maximum cost-effectiveness without sacrificing diagnostic accuracy.

Anemia↗
PubMed1991

Dual task performance and processing resources in normal subjects and patients with Parkinson's disease.

In recent years, there has been a growing consensus among investigators that the presence or absence of external cues guiding behaviour and attention is an important factor in determining whether or not deficits are found in patients with Parkinson's disease (PD). In an earlier study, the authors suggested that the pattern of impaired and intact performance could be explained in terms of differential resource demands of the tasks, combined with depleted levels of central processing resources in PD patients. Two experiments are reported, both employing dual-task paradigms. The first assessed, in normal subjects, the relative processing demands of a cued and an uncued version of the Stroop task. The results supported the proposal that the noncued task made greater demands on the subject's limited processing resources. Further, performing a resource demanding secondary task concurrently with the Stroop test produced, in normal subjects, the same pattern of impaired performance as that reported previously in PD patients. In the second experiment the same dual-task paradigm was employed with a group of PD patients and normal aged-matched controls. Only the patients showed an increase in reaction time on the Stroop task when performing a resource demanding secondary task. The patients also showed an interfering effect with concurrent foot tapping but not with an articulatory suppression task. The results were taken to support the hypothesis that PD patients have depleted central processing resources. In considering the present data, alternative explanations for the results are considered, in particular the possibility that they represent a deficit in switching processing resources between two tasks as the combined demands outweigh available resources.

Adult↗
PubMed1990

Structural studies of the capsular polysaccharide from Aerococcus viridans var. homari.

The capsular polysaccharide from Aerococcus viridans var. homari has been investigated, using n.m.r. spectroscopy, methylation analysis, and specific degradations as the main methods. The polysaccharide is composed of tetrasaccharide repeating-units having the following structure. (Formula; see text) In this structure, D-QuiN stands for 2-amino-2,6-dideoxy-D-glucose (quinovosamine). Two of the three acidic sugars found, namely, L-altruronic acid and 4-O-[(S)-1-carboxyethyl]-D-glucose, have not been found in any other natural source. As evident from the n.m.r. spectra, the L-altruronic acid is not present in the 1C4 conformation, but flips to a conformation close to this on carboxyl reduction.

Carbohydrate Sequence↗
PubMed1990

Cognitive function in Parkinson's disease: from description to theory.

From the large body of empirical evidence on cognitive function in Parkinson's disease, a number of attempts have been made to describe the characteristics of the deficits and the conditions under which they are observed. This review considers descriptions limited to specific domains of cognition such as visuospatial function, memory and 'frontal' function, and more general descriptions relating to 'set-shifting', sequencing, temporal ordering and recency discrimination, the locus of cognitive control and bradyphrenia. Later in the paper an attempt is made to provide some theoretical framework for the various descriptions. Two theories are discussed representing contrasting, but complementary approaches. The first is a 'psychological' theory in which the concept of depleted processing resources is suggested as a possible mechanism to explain the observable deficits. The second is a neurobiological model that attempts to integrate information from diverse sources to provide a model for the neuroanatomical and neurochemical substrate that may underlie some of the behavioural deficits.

Caudate Nucleus↗
PubMed1990

Psychiatric morbidity in patients with Parkinson's disease.

Forty patients with Parkinson's disease underwent a detailed assessment of their psychiatric state using a standardized, semi-structured interview, the Present State Examination. Analysis of the interviews yielded a profile of depressive and neurotic syndromes. Comparing the results with population norms, however, revealed that the patients were distinguished only by high levels of depressed mood and loss of interest and poor concentration. In the majority of patients the range and severity of symptoms fell below the criteria for 'caseness'. Only four patients could be allocated to an ICD-9 class, two to 'neurotic depression', one to 'anxiety state' and one to 'phobic state'. This rate was almost identical to that found in the general population. Broader indices of psychiatric morbidity were related to the patients' levels of disability and cognitive function.

Activities of Daily Living↗
PubMed1990

Sexual function in patients with Parkinson's disease and their partners.

Sexual function in patients with Parkinson's disease has received virtually no attention. There are many reasons (physical, psychological and social), why such patients might experience problems within their sexual relationships. A group of patients and their partners completed a series of self-report measures, aimed at assessing sexual function and a range of factors which might be associated with any difficulties. The results revealed a high level of dysfunction, not just in the patients but also in their partners. Most effected were the couples in which the patient was male. A range of problems were reported by both patients and their partners. These were, in turn, associated with a range of variables relating to the disease, psychological and social factors. No simple causal model was suggested, and a multimodal therapeutic approach might be expected to have most benefit.

Activities of Daily Living↗
PubMed1989

Dirofilariasis.

Explore the source record for details and available documents.

Animals↗
PubMed1989

Accuracy of self-reported disability in patients with parkinsonism.

For the patient, the most important aspect of parkinsonism is the degree to which the disease interferes with daily living. The patient's self-report may be the only way in which such information can be obtained. Depression and cognitive impairment, however, may influence that self-report. In the present study, three ratings of disability, from the patient, a relative, and an independent observer, showed high levels of agreement. The patients' cognitive function made a small but significant contribution to the accuracy of their self-report judged against the relative's rating. Depression, however, played no role. Agreement between patients and relatives for individual items on the disability questionnaire was reasonably high. The results suggest that patients with parkinsonism can provide accurate self-report of their level of disability, even in the presence of depression and cognitive impairment.

Activities of Daily Living↗
PubMed1988

An investigation of the phenomenon of "set" in Parkinson's disease.

It has been suggested that patients with Parkinson's disease have a basic deficit in shifting "set." Previous authors have used this hypothesis as an explanation for deficits on a range of cognitive tasks. An experiment was conducted to investigate this phenomenon. A reaction time paradigm was used in which the subject had to make left-right decisions under two stimulus conditions. Both patients and controls showed a facilitation in performance with repetition within each block of trials, followed by a deterioration in performance when the stimulus type switched. Furthermore, the shapes of the reaction-time functions were equivalent in both groups, suggesting that the patients had no deficit in either switching or establishing set in this task. In contrast, they were impaired on the Wisconsin Card Sorting Test. This dissociation suggests that patients with Parkinson's disease do not have a generalized deficit in switching set. It is suggested that patients with Parkinson's disease are impaired on tasks where they have to rely upon internal control for the regulation of behaviour, but are relatively unimpaired on tasks where external cues are available.

Aged↗
PubMed1988

Determination of protein size in chromatography column eluants by on-line photon correlation spectroscopy.

The dynamic light scattering technique of photon correlation spectroscopy has been used to determine biomacromolecule hydrodynamic radius in solutions flowing at rates similar to those experienced in liquid chromatographic separation systems. Such analyses can be performed rapidly (less than 5 s). The potential of the technique as an on-line noninvasive monitor for liquid chromatography is discussed.

Light↗
PubMed1988

Depression and disability in Parkinson's disease: a follow-up of 132 cases.

Patients with Parkinson's disease, 132 in number, were followed up after approximately one year, and measures of depression and disability re-administered. Depression was common on both occasions, and was characterized by dysphoria, pessimism and somatic symptoms, but not guilt or self-blame. Depression and disability were associated on both occasions. The relationship between changes in disability and depression across time was complex. In trying to understand changes in depression, the absolute change in disability may be less important than the relative change and rate of change. The results were discussed in relation to findings from other disease groups, and the implications for the clinical management of depression in Parkinson's disease.

Activities of Daily Living↗
PubMed1988

'Frontal' cognitive function in patients with Parkinson's disease 'on' and 'off' levodopa.

A wide range of cognitive impairments can be observed in patients with Parkinson's disease. A close parallel exists between these deficits and those found following damage to prefrontal cortex. Anatomical evidence is reviewed which reveals a complex pattern of neuronal circuits connecting the frontal cortex and basal ganglia. All these circuits are in some way dependent upon dopamine, suggesting that changes in the levels of dopamine stimulation may alter performance on 'frontal' tests. To test this hypothesis, a group of patients with Parkinson's disease were assessed both on and off levodopa treatment, on a range of tests selected from the human and animal experimental literature as being sensitive to disruption of prefrontal cortex. A variable pattern of results was obtained. On one test, a measure of verbal fluency, patients were impaired, compared with normal controls, only when off levodopa. On two measures, associative conditional learning and subject-ordered pointing, patients were impaired only when on levodopa, while on the final measures, the Wisconsin Card Sorting Test, patients were impaired both on and off levodopa. Two mechanisms are discussed to explain these results, one based on the effects of dopamine depletion, and the other based on the adverse effects of dopamine overstimulation. The results suggest that different areas of prefrontal cortex are involved in the tasks employed, and that functional levels of dopamine in separate areas of cortex and caudate may differ crucially in Parkinson's disease.

Aged↗
PubMed1988

Internal versus external cues and the control of attention in Parkinson's disease.

In recent years, several attempts have been made to characterize the nature of the cognitive deficits shown by patients with Parkinson's disease. It has been suggested variously that they have difficulty in switching cognitive set, in performing effortful (or controlled) as opposed to automatic tasks, or that their impairment is found in tasks which maximize the amount of 'self-directed task specific planning'. It is proposed that this latter distinction may be reformulated in terms of the degree of internal versus external attentional control which is required by the task. An experiment is described which attempted to manipulate this parameter. A version of the Stroop colour-word test was used, in which the words 'red' and 'green' were presented in the complementary coloured 'ink'. Subjects responded either to the colour of the ink in which the word was written or the colour named by the word. The relevant attribute changed at intervals during the course of the experiment. In one condition, the relevant stimulus attribute was cued before each trial. In another condition, subjects had to remember which attribute was currently relevant. Results revealed that patients with Parkinson's disease were impaired mainly on the second version of the task which required internal attentional control. The results are discussed in relation to the models of Working Memory (Baddeley, 1986), and attentional control (Norman and Shallice, 1980). Exploration of these models leads to the formulation of a theory in which the crucial determinant of cognitive impairment in Parkinson's disease is reduced resources in the Supervisory Attentional System. Provided the demands of the task are within the patient's available attentional resources the patient may not show any deficit. If, however, the attentional demands exceed available resources, as in tasks which depend upon internal cues, then deficits will be observed.

Attention↗