Biomedical subjects

David R Hemsley

Publications and source records attributed to David R Hemsley.

11 recordsLinked to original sources

PubMed2006

Schizotypy and creativity in visual artists.

'Every work of art is an uncommitted crime' Adorno (1951). Cited in Julius (2002). Given the putative relationship between creativity and schizotypy/psychoticism, the current study set out to investigate differences in scores on a range of personality and creativity measures between visual artists and non-artists. Results found that the visual artists group scored higher on measures of positive-schizotypy, disorganized-schizotypy, asocial-schizotypy, neuroticism, openness and divergent thinking (uniqueness) than did the non-artist group and lower on agreeableness. These findings lend support to other studies reporting higher schizotypy scores in artistic and creative cohorts, although provide some of the first evidence of higher unusual experiences and impulsive nonconformity scores on the Oxford-Liverpool Inventory of Feelings and Experiences (O-LIFE) in visual artists. The relationship between creativity and schizotypy is discussed in terms of unusual ideas and a propensity to endorse socially undesirable responses.

Adult↗

PubMed2005

The schizophrenic experience: taken out of context?

A currently favored cognitive model of the abnormal behaviors and experiences characteristic of schizophrenia suggests that they may be linked to a disturbance in the effects of context. The present article reviews some of the relevant literature, noting the wide range of experimental paradigms that have been employed. This range of paradigms is both a strength and a potential weakness of the literature because it raises complex issues of definition and the need to distinguish the various ways that context may influence behaviors. This influence may be crucially dependent on specific task parameters. Despite this, a number of phenomena can be plausibly related to changes in the way that context operates: delusions, disorganization, hallucinations, and the loss of a sense of personal identity. Potential links with the neural bases of the disorder are indicated.

Cognition Disorders↗

PubMed2005

Disruption of learned irrelevance in acute schizophrenia in a novel continuous within-subject paradigm suitable for fMRI.

Learned irrelevance (LIrr) is closely related to latent inhibition (LI). In LI a to-be-conditioned stimulus (CS) is prexposed alone prior to the opportunity to learn an association between the CS and an unconditioned stimulus (UCS). In LIrr preexposure consists of intermixed presentations of both CS and UCS in a random relationship to each other. In both paradigms preexposure leads in normal subjects to reduced or retarded learning of the CS-UCS association. Acute schizophrenics fail to show LI. LI is usually demonstrated as a one-off, between-groups difference in trials to learning, so posing problems for neuroimaging. We have developed a novel, continuous, within-subject paradigm in which normal subjects show robust and repeated LIrr. We show that this paradigm is suitable for functional magnetic resonance imaging (fMRI) and gives rise, in normal subjects, to activation in the hippocampal formation, consistent with data from animal experiments on LI. We also report, consistent with previous studies of LI, loss (indeed, significant reversal) of LIrr in acute (first 2 weeks of current psychotic episode) schizophrenics. Chronic schizophrenics failed to demonstrate learning, precluding measurement in this group of LIrr. These findings establish the likely value of the new paradigm for neuroimaging studies of attentional dysfunction in acute schizophrenia.

Adult↗

PubMed2005

The development of a cognitive model of schizophrenia: placing it in context.

This review provides a historical perspective on a model for schizophrenia based on results of experiments derived from learning theory. It was developed by the author in collaboration with Jeffrey Gray and numerous colleagues, (e.g. [Gray, J.A., McNaughton, N., 2000. The Neuropsychology of Anxiety. second ed. Oxford University Press, Oxford; Hemsley, D.R., 1987a An experimental psychological model for schizophrenia. In: Hafner, H., Gattaz, W.F., Janzarik, W. (Eds.), Search for the Causes of Schizophrenia, vol. 1. Springer, New York, pp. 179-188.; Hemsley, D.R., 1993. A simple (or simplistic?) cognitive model for schizophrenia. Behaviour Research and Therapy 31, 633-646]. It contrasts with earlier cognitive formulations [e.g. Hemsley, D.R., 1975. A two stage model of attention in schizophrenia research. British Journal of Social and Clinical Psychology 14, 81-88], which emphasised a weakening of contextually elicited response biases, and lacked a link to potential neural bases of the disorder. The model emphasizes the need to demonstrate patterns of performance that are not interpretable in terms of the well established 'generalized deficit' manifest in schizophrenia. It proposes that the cognitive disturbance is a change in the way stored material is integrated with sensory input and ongoing motor programmes. In particular, spatial and temporal context fail to activate appropriate stored regularities. A number of possible pathways from the cognitive disturbance to the symptoms of schizophrenia are outlined; again the term 'context' is widely employed. Thus, it has been invoked to explain the occurrence of hallucinations, delusions, thought disorder and disruptions in the sense of personal identity. However the term 'context' is ill-defined and the review indicates the variety of ways in which it may exert its influence. These are unlikely to reflect the operation of a unitary mechanism.

Animals↗

PubMed2004

Trials-to-criterion latent inhibition in humans as a function of stimulus pre-exposure and positive-schizotypy.

Latent inhibition (LI) is a phenomenon during which non-reinforced pre-exposure to a stimulus retards later learning of associations with that same stimulus. It has been suggested that LI is a positive function of the amount of stimulus pre-exposure (PE) and that with very small amounts of PE, facilitation rather than inhibition will occur-particularly in high positive-schizotypes. Although LI has been demonstrated as a function of the amount of pre-exposure in animals, human findings have not proved to be so uniform or consistent. The primary objective of the present study was to establish LI as a function of numbers of pre-exposure on visual and auditory trials-to-criterion tasks, with a secondary objective to establish latent facilitation (LF) with very low numbers of pre-exposure in high positive-schizotypes. Results revealed a uniform pattern of learning across pre-exposure conditions, including latent facilitation, on the visual, but not the auditory task. LF was also observed in the high, but not low, scorers in positive-schizotypy with very low numbers of pre-exposure on the visual task.

Acoustic Stimulation↗

PubMed2003

Electrodermal responsivity distinguishes ERP activity and symptom profile in schizophrenia.

BACKGROUND: Traditional averaging of late component Event Related Potentials (ERPs) might obscure important psychophysiological subprocesses underlying schizophrenia disturbances in cognitive functioning. One such subprocess could be the active orientation of attention to significant or novel stimuli. In this study, we used skin conductance responses (SCRs) to index orienting responses (ORs). ERP activity was examined in relation to concomitant ORs in a schizophrenia and nonpsychiatric control group. Schizophrenia responses were considered with respect to the Reality Distortion, Disorganisation and Psychomotor Poverty syndromes. METHOD: Forty schizophrenia and 40 age and sex matched control subjects were tested. The three schizophrenia syndromes were derived from a principal component analysis of Positive and Negative Syndrome Scale (PANSS) ratings. Auditory ERPs (N100, N200, P200, P300) were elicited using a conventional auditory oddball paradigm, and electrodermal SCR data were acquired simultaneously. RESULTS: ERP data were sub-averaged according to the presence/absence of an OR. For both 'with-' and 'without-OR' ERPs, schizophrenia subjects as a group showed reduced N100 (associated with vigilance level) and N200 (associated with response selection) amplitude, and for with-OR responses, they showed an additional reduction in P300 (context processing). Concerning schizophrenia syndromes, Reality Distortion was related primarily to frontal disturbances (earlier N100/N200 latency and decreased P200/P300 amplitude), and Psychomotor Poverty to a generally delayed P300 latency. Similarly delayed P300 in Disorganisation was explained by medication effects. There were no associations with syndromes for without-OR ERPs. CONCLUSION: These results suggest that schizophrenia syndromes are dissociated with regard to both the direction and nature of speed of information processing disturbances, in relation to task-relevant information that produces active orientation.

Adolescent↗

PubMed2003

A demonstration of within-subjects latent inhibition in the human: limitations and advantages.

The magnitude of latent inhibition (LI) (a retardation of associative learning due to prior exposure to the conditioning stimulus) was measured in healthy volunteers using both a within- and a between-subjects version of the task. Reliable LI was demonstrated for the within-subjects paradigm (using a design that fully counter-balanced stimulus of pre-exposure) but the magnitude of the effect was smaller than for the between-subjects version. Measures of schizotypal personality were found to be associated with reduced LI for the between-subjects task, but not for the within-subjects task. We hypothesised that for the within-subjects task learning about the first stimulus-consequence association (usually that for the not pre-exposed (NPE) stimulus) primes learning about the second stimulus, thus reducing the effect of pre-exposure and restricting the range of LI scores. In turn, this restricted range of LI scores does not allow subtle differences on schizotypal personality dimensions to reveal their effect using this within-subjects paradigm. In conclusion, a within-subjects LI task has been developed which is not open to explanation in terms of differences in stimulus salience. However, the limited range of pre-exposure scores in the current within-subject paradigm may severely limit it is use as an indicator of subtle performance changes.

Adolescent↗

PubMed2003

Low dose ketamine increases prepulse inhibition in healthy men.

The N-methyl-D-aspartate (NMDA) antagonist, ketamine, produces neurobehavioural symptoms that mimic aspects of schizophrenia. Prepulse inhibition (PPI) of the startle reflex, a measure of sensorimotor gating, is decreased in chronically ill, medicated schizophrenic patients and in animals treated acutely with NMDA antagonists. We tested the hypothesis that ketamine would produce psychotic symptoms and reduce PPI in healthy humans. Twenty male volunteers received placebo and ketamine in a within-subject, double-blind, cross-over design with 0.23 mg/kg ketamine hydrochloride or saline as a loading dose, followed by 0.5 mg/kg ketamine or saline over 45 min. Prepulse to pulse intervals were 30 ms and 120 ms. The Brief Psychiatric Rating Scale (BPRS) and the Clinician Administered Dissociative States Scale (CADSS) were administered. Ketamine produced a significant increase in PPI and significantly reduced startle magnitude, but did not alter habituation. Ketamine produced significant increases in BPRS and CADSS scores, with symptoms mimicking the negative and disorganisation symptoms of psychosis. In contrast to effects in rodents, this low dose of ketamine produced an increase in PPI despite producing psychopathological symptoms consistent with the NMDA psychosis model. These findings suggest that the cognitive and PPI changes of NMDA antagonists are not consistently linked at a phenomenological or neurochemical level.

Acoustic Stimulation↗

PubMed2002

The partial reinforcement extinction effect in humans: effects of schizophrenia, schizotypy and low doses of amphetamine.

The partial reinforcement extinction effect (PREE) was studied in human subjects. It has been suggested that the PREE depends on neural mechanisms critical to the cognitive dysfunction which underlines acute schizophrenia. We therefore predicted that the PREE should be reduced, through decreased resistance to extinction in the partial reinforcement (PR) condition, in various types of individual: (a) healthy volunteers given low doses of oral amphetamine; (b) those in the acute (but not chronic) phase of a schizophrenic illness and; (c) healthy volunteers with high scores on personality measures of schizotypy. Despite obtaining robust demonstrations of PREE in all experiments, none of these predictions were confirmed. A single, low dose, of amphetamine had no effect on either continuous reinforcement (CR) or partial reinforcement (PR). Acute and chronic schizophrenic patients showed a reduced PREE compared to controls. However this was due to increased resistance to extinction in the CR groups. Finally, high schizotypy scores were associated with greater PREE, attributable to both decreased extinction in the CR condition and increased extinction in the PR condition. The results of these experiments on human PREE provide no support that PREE is a valid paradigm with which to explore the cognitive dysfunction underlying schizophrenia.

Acute Disease↗

PubMed2002

Perceptual organization deficits in psychotic patients.

It has been proposed that a characteristic of schizophrenic processing is an abnormality of top-down processing. The relationship between impaired top-down processing and symptoms of reality distortion was investigated using a 'degraded interference' task. In this task, fragmented stimuli (Stroop words, control words and crosses) are presented on a computer screen, and the extent to which they are visually integrated is inferred by their interfering properties. It was predicted that psychotic individuals would fail to show an interference effect with degraded Stroop stimuli. This predicts the absence of a delay in reaction time in the experimental condition, which therefore cannot be attributed to a generalized deficit. A sample of inpatients experiencing positive symptoms was compared to a healthy control group. The results provided support for a deficiency in top-down processing, with the psychotic group failing to show the significant degraded interference effect found in the healthy controls. Degraded interference was associated with low verbal IQ, but with no other symptomatic or demographic variables.

Adult↗

PubMed2000

The relationship between cognitive inhibition and psychotic symptoms.

Cognitive models of schizophrenia have highlighted deficits of inhibitory attentional processes as central to the disorder. This has been investigated using "negative priming" (S. P. Tipper, 1985), with schizophrenia patients showing a reduction of negative priming in a number of studies. This study attempted to replicate these findings, but studied psychotic symptoms rather than the broad diagnostic category of schizophrenia. Psychotic individuals exhibiting positive symptoms were compared with asymptomatic psychiatric patients and with a normal control group. As predicted, the symptomatic group failed to show the usual negative priming effect, which was present in the asymptomatic and normal groups. A modest but significant correlation was found between negative priming and delusions. Neither diagnosis, nor affective or negative symptoms, nor chronicity, nor medication, was related to negative priming. These data replicate previous findings that positive symptoms are related to a reduction in cognitive inhibition, although considerable variability was observed among the psychotic patients.

Adult↗