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Biomedical subjects

A S David

Publications and source records attributed to A S David.

At least 127 records · Page 7Linked to original sources
PubMed1995

Psychotic states arising in late life (late paraphrenia). The role of risk factors.

BACKGROUND: This study explored the association between 'late paraphrenia' and various risk factors such as female gender, sensory impairment, marital status, positive family history of psychoses, and the presence of abnormal neurological signs. It was hypothesised that patients would show significantly more abnormal neurological signs than controls. METHOD: Inclusion criteria for the diagnosis of late paraphrenia were fulfilled by 47 patients, including in-patients, out-patients, day-patients, and those living in the community. Thirty-three age-, sex-, education-, and premorbid IQ-matched elderly controls were recruited from luncheon clubs in Southwark and Lambeth (London, UK). A scale for the assessment of neurological soft and hard signs was developed for this study. The Abnormal Involuntary Movement Scale (AIMS) and the Tardive Dyskinesia Rating Scale (TDRS) were also used. RESULTS: There was a high female-to-male ratio (42:5), and a fourfold increase in the risk of patients having hearing impairment (odds ratio = 4.15, Clodds = 1.36 to 12.63). There was no difference between the two groups in visual difficulties nor in marital status. Patients were approximately ten times more likely to be living on their own (odds ratio = 10.61; Clodds = 3.59 to 31.33) and 16 times more likely to be considered socially isolated (odds ratio = 16.65; Clodds = 5.39 to 51.40). There was no difference between patients and controls in frequency of schizophrenia-like family history. Patients were more likely than controls to exhibit neurological soft signs (z = 4.70; P < 0.001; Cld = 4.61 to 9.63). The presence of abnormal involuntary and tardive dyskinesia movements was associated with the use of antipsychotic medication. CONCLUSION: Women appear to run a greater risk of developing late paraphrenia, especially those who are socially isolated and present with associated hearing impairment. The increased presence of neurological soft signs among patients indicates that brain disease may be a critical factor in the development of psychotic symptoms in late life.

Aged↗
PubMed1994

Schizophrenia and the corpus callosum: developmental, structural and functional relationships.

Several empirical and theoretical connections exist between schizophrenia and the corpus callosum: (1) disconnection symptoms resemble certain psychotic phenomena; (2) abnormal interhemispheric transmission could explain typically schizophrenic phenomena; (3) cases of psychosis have been found in association with complete and partial agenesis of the callosum; (4) experimental neuropsychology with schizophrenic patients has revealed abnormal patterns of interhemispheric transfer; (5) studies using magnetic resonance imaging have shown abnormal callosal dimensions in schizophrenic patients. The evidence in support of these links is discussed critically. Novel neuropsychological approaches in the study of information transfer in the visual modality between the cerebral hemispheres, consistent with callosal hyperconnectivity in schizophrenic patients but not matched psychiatric controls are highlighted. Some suggestions for further work including integrating functional and structural measures are offered.

Agenesis of Corpus Callosum↗
PubMed1994

Regional cerebral blood flow (rCBF) in schizophrenia during verbal memory activation: a 99mTc-HMPAO single photon emission tomography (SPET) study.

Regional cerebral blood flow (rCBF) was investigated in a group of medicated DSM-III-R schizophrenic patients and age, sex and handedness matched normal volunteers using a split-dose 99mTc-HMPAO Single Photon Emission Tomography (SPET) protocol. Measures were taken during the performance of a verbal memory task aimed at activating the left medial temporal lobe, a region repeatedly suggested to be structurally abnormal in schizophrenia. In normal subjects, the performance of the task was associated with significant rCBF increases in the left medial temporal, left inferior frontal and anterior cingulate cortices, and right cerebellum. Despite their significantly poorer performance on the memory task, the degree of medial temporal activation measured in the schizophrenic patients was not significantly different from that found in the control group. This finding suggests that memory deficits in schizophrenia do not necessarily imply failure to activate the left medial temporal lobe as assessed by 99mTc-HMPAO SPET.

Adult↗
PubMed1994

An experimental phenomenological approach to delusional memory in schizophrenia and late paraphrenia.

A preliminary model is described to account for the 'reality testing' of memories (after Johnson & Raye, 1981) in an attempt to explain delusional memory. Two routes are proposed: route one involves evaluation of the factual content of the memories against stored general knowledge. Route two relies on the evaluation of the perceptual and narrative characteristics of memories with the assumption that the stronger these characteristics, the more likely the memory is to be real. The integrity of these routes is examined in four patients with delusional memories, using standardized tests. The results suggest that in these cases, general knowledge is essentially intact while the perceptual characteristics of delusional memories are stronger than real memories which in turn, are stronger than fantasies. This could lead the evaluation system to accept delusional memories as true memories despite their implausibility. The roles of rehearsal and affect are probably important in this and require further study.

Adult↗
PubMed1994

Dysmodularity: a neurocognitive model for schizophrenia.

Hoffman and McGlashan's introduction of the term neurodynamics prompts a neurocognitive account of schizophrenia along the same lines, called "dysmodularity." In cognitive terms dysmodularity describes an impairment in the function of specialized processors due to a breakdown in one of their prime attributes: informational encapsulation. In neural terms dysmodularity implies increased structural and functional connectivity, reduced anatomical specialization such as lateral asymmetries, and increased white matter in relation to gray. Reduced cortical pruning would be one mechanism for dysmodularity. This model is opposite to the excessive pruning model proposed by Hoffman and McGlashan, but we believe it is more firmly supported by the literature, including some articles in the same issue of Schizophrenia Bulletin (Vol. 19, No. 1, 1993).

Attention↗
PubMed1994

Understanding the symptoms of schizophrenia using visual scan paths.

BACKGROUND: This paper highlights the role of the visual scan path as a physiological marker of information processing, while investigating positive symptomatology in schizophrenia. METHOD: The current literature is reviewed using computer search facilities (Medline). RESULTS: Schizophrenics either scan or stare extensively, the latter related to negative symptoms. Schizophrenics particularly scan when viewing human faces. CONCLUSIONS: Scan paths in schizophrenics are important when viewing meaningful stimuli such as human faces, because of the relationship between abnormal perception of stimuli and symptomatology in these subjects.

Attention↗
PubMed1993

Spatial and selective attention in the cerebral hemispheres in depression, mania, and schizophrenia.

Two tachistoscopic tests examining distinct aspects of attention were administered to normal subjects and patients with depression, mania, and schizophrenia. The first examined spatial attentional bias using happy-sad chimeric faces, known to elicit a perceptual bias to the left side of space in normal right-handers provided the right cerebral hemisphere is intact. The second used a lateralized version of the Stroop task, a traditional test of selective attention. Normals showed the expected leftward perceptual bias but showed equivalent susceptibility to the Stroop effect in both visual fields. As previously demonstrated with chimeric faces viewed in free vision, depression and mania were associated with weak and strong biases respectively with schizophrenics showing no bias to either side of space. The relationship between perceptual bias, as assessed by reaction time and absolute performance and the Stroop effect, showed differences according to diagnosis. This may be interpreted as evidence for the dissociability of attentional processes as well as lateralized differences in the pattern of cerebral activation in affective disorders and schizophrenia. The independence of performance variables on these tests in the schizophrenic group points to severe neuropsychological dysfunction.

Adult↗
PubMed1993

Visual imagery and visual semantics in the cerebral hemispheres in schizophrenia.

Divided visual field tasks were given to normal subjects, and patients with schizophrenia and affective disorder, to investigate hemisphere differences in the visual processing of standardised pictorial stimuli. There were two conditions: in the first, subjects were asked to decide whether a common entity represented by a picture was living or non-living, a task involving a categorical judgement based on semantic information; a left hemisphere task. In the second condition, subjects judged whether these depictions represented entities which were bigger or smaller than a cat; a right hemisphere task requiring visual imagery to compare spatial dimensions. It was found that the patient groups, while showing slower reaction time (RT) overall, both displayed a right hemisphere (RH) advantage on the imagery task. Furthermore, the schizophrenics' RHs showed the normal relationship between closeness of size comparison and RT, additional evidence that the visual imagery mechanism is intact. However, these patients failed to show the expected left hemisphere advantage on the visual-semantic task. There was a suggestion that performance on the semantic task was related to the experience of vivid imagery in normals and visual hallucinations in the schizophrenics. The possible contribution of hemispheric imbalance in the production of visual hallucinations from a disordered semantic system is discussed.

Adult↗
PubMed1993

Chronic fatigue in primary care attenders.

From 686 patients attending primary care physicians, 77 were identified by a screening procedure as having chronic fatigue. Of these, 65 were given a comprehensive psychological, social and physical evaluation. Seventeen cases (26%) met criteria for the chronic fatigue syndrome. Forty-seven (72%) received an ICD-9 diagnosis of whom 23 had neurotic depression, with a further 5 meeting criteria for neurasthenia. Forty-nine were 'cases' as defined by the revised Clinical Interview Schedule (CIS-R), and 42 if the fatigue item was excluded. Psychiatric morbidity was more related to levels of social stresses than was severity of fatigue. The main difference between these subjects and those examined in hospital settings is that the former are less liable to attribute their symptoms to wholly physical causes, including viruses, as opposed to social or psychological factors. Identification and management of persistent fatigue in primary care may prevent the secondary disabilities seen in patients with chronic fatigue syndromes.

Adult↗
PubMed1993

Callosal transfer in schizophrenia: too much or too little?

Evidence from diverse sources has pointed to an abnormality in callosal transfer in schizophrenia. To examine this further, a test was devised that measures Stroop interference and facilitation within and between the cerebral hemispheres. 46 heterogeneous schizophrenic patients were tested, and it was found that lateralized Stroop effects were equivalent in the left and right hemispheres and did not differ from normal or psychiatric (affective disorder) control Ss. In control Ss, Stroop effects that required interhemispheric transfer of coded information were reduced relative to those requiring intrahemispheric transfer, whereas among schizophrenic Ss, greater Stroop effects were found in the interhemispheric condition, presumably reflecting increased callosal connectivity. An index of callosal transfer did not correlate with gender, age, or IQ in any of the groups, nor did it relate to clinical characteristics in the schizophrenic Ss. The results support a specific functional abnormality of excessive callosal transfer in schizophrenia, though its role in pathogenesis remains unspecified.

Adult↗
PubMed1993

Auditory-verbal hallucinations and the phonological loop: a cognitive neuropsychological study.

A patient with continuous auditory-verbal hallucinations was studied, in comparison with two cases with a past history of similar hallucinations, from a cognitive neuropsychological perspective. This attempts to place hallucinations in the context of a normal cognitive process which has become disordered. The process in question is the phonological loop, equivalent to inner speech, derived from a model of short-term or working memory. A series of short-term memory tests, assumed to rely on the adequate functioning of the phonological loop, was administered, the results of which broadly conformed to a normal pattern of performance. It is concluded that verbal hallucinations cannot be regarded as involving the phonological loop directly. Other points in the short-term memory/language system at which verbal hallucinations could arise are discussed, as are suggestions for further research of this kind.

Adult↗
PubMed1993

Severe psychiatric disturbance and abnormalities of the corpus callosum: review and case series.

The association between developmental defects of the corpus callosum and major psychiatric disturbance is discussed with a review of published cases. Seven new cases are presented, of which four had clear psychotic symptoms, two receiving a diagnosis of schizophrenia. Of the remainder, one had a developmental disorder affecting social interaction and speech which could be classed as Asperger's syndrome, one had a personality disorder with depressive and conversion symptoms, and the last was an adolescent boy with severe behavioural problems. The difficulties in determining the precise relevance of the callosal anomalies to these clinical manifestations are discussed especially since the prevalence of such anomalies in the population is uncertain.

Adult↗
PubMed1992

Stroop effects within and between the cerebral hemispheres: studies in normals and acallosals.

Interference and facilitation of tachistoscopically presented colour stimuli by adjacent incongruent and congruent colour-words (the Stroop effect) was examined in the right and left visual fields, and centrally, in normal subjects and three acallosals. In the central condition, the word and colour were each separated across the fovea. Normal subjects showed a small left hemisphere advantage for colour naming. The combined Stroop effect (CSE), that is the reaction time difference between incongruent and congruent pairs, was the same in both visual fields but reduced centrally. Furthermore, in the central condition, the CSE was the same regardless of the side on which the word or colour appeared. The reduced CSE in the central condition was exaggerated in one of the acallosals, suggesting that the corpus callosum, by acting as a partial barrier, mediates the interhemispheric Stroop effects. The other acallosals while providing some tentative support for this, showed evidence of lateralized dysfunctions to that their performance was less easily interpreted. The methodology described would appear to have applications in studying the functional characteristics of the corpus callosum in a variety of clinical groups.

Adult↗