Biomedical subjects

P Maruff

Publications and source records attributed to P Maruff.

At least 55 records · Page 3Linked to original sources

PubMed2000

The neuropsychology of preclinical Alzheimer's disease and mild cognitive impairment.

Subjects in the preclinical stages of Alzheimer's disease (AD) typically record neuropsychological performance between that of healthy older individuals and demented patients. More specifically, deficits on measures of verbal episodic memory are commonly reported in these patients, while other cognitive functions (e.g. language, praxis and executive function) seem to be spared. A similar neuropsychological profile is observed in elderly subjects with mild cognitive impairment (MCI), a disorder that is attracting increasing research interest. Evidence from lesion and functional imaging studies, as well as volumetric imaging in probable AD and MCI patients, suggests that the cognitive deficits observed in these disorders may be related to medial temporal lobe dysfunction. An issue currently under investigation is whether MCI represents the preclinical stages of AD or a distinct and static cognitive aetiology. In an attempt to address this issue, present investigations are adopting a convergent approach to the detection of preclinical AD, where multiple risk factors are considered when making a diagnosis.

Alzheimer Disease↗

PubMed2000

The effect of an external load on the force and timing components of mentally represented actions.

The chronometry of real and imagined movements was investigated in a group of eight subjects under varying conditions. The visually-guided pointing task was used to investigate the speed for accuracy trade-offs that occur as target size is varied for both real and imagined performance. The task was performed both with and without an external load of 2 kg. For the no-load condition and load conditions, the speed for accuracy trade-off for both real and imagined performance conformed to Fitts' law. Movement durations of real movements remained largely unaffected by the addition of the load, however, movement durations of imagined movements increased significantly with the addition of the load. These patterns of results suggest that the weight disrupted the force calculation component of imagined movements but not the relative timing.

Adult↗

PubMed2000

Spatiotemporal distribution of facilitation and inhibition of return arising from the reflexive orienting of covert attention.

Currently, there is debate regarding both the spatial and temporal relationship between facilitation and inhibition of return (IOR) components of attention, as observed on the covert orienting of visual attention task (COVAT). These issues were addressed in a series of experiments where the spatial and temporal relationships between cue and target were manipulated. Facilitation occurred only when the stimulus onset asynchrony (SOA) was short and there was temporal overlap between cue and target. IOR occurred only when SOA was long and there was no temporal overlap between cue and target. Facilitation encompassed the cued location and all locations between the cue and fixation, whereas IOR arose for the entire cued hemifield. These findings suggest that the facilitation and IOR found on COVATs that use noninformative peripheral cues are separable and stimulus-driven processes.

Adult↗

PubMed2000

Goal-directed selective attention and response competition monitoring: evidence from unilateral parietal and anterior cingulate lesions.

Competing visual stimuli lead to slower responses to targets. This response competition must be resolved before correct responses are executed. Neuroimaging suggests that response competition monitoring may be subserved by an integrated neural network including the anterior cingulate cortex (ACC). In this study, 1 patient with a parietal lesion (Patient J.S.) and 1 with an ACC lesion (Patient G.M.) were presented with 2 flanker tasks; 1 required verbal identification of color targets, and the other required an opposite response to targets (e.g., see red and say "green"); a control group was also tested. For controls, perceptually incongruent flankers interfered with the ability to inhibit prepotent responses to targets. Patient J.S. performed in a similar manner, even when flankers appeared in the neglected field. Patient G.M. demonstrated reduced interference effects for contralesional flankers. Results are discussed in terms of goal-directed selective attention and response competition monitoring.

Adult↗

PubMed2000

Magnetic resonance spectroscopy and schizophrenia: what have we learnt?

OBJECTIVE: Magnetic resonance spectroscopy (MRS) has been increasingly used to investigate the in vivo biochemistry of particular regions of the brain in patients with schizophrenia. We review the literature and discuss the theoretical constructs that form the presumed impetus for these studies in light of the current methodological limitations. Future directions are noted. METHOD: The available published literature in English formed the basis for this review. RESULTS: The results of 31P-MRS have been interpreted as reflecting a relative increase in cell membrane degradation in prefrontal cortical regions at certain phases of schizophrenia. 1H-MRS studies, though less consistent, provide evidence suggestive of a decrease in neuronal cell mass in the hippocampal region, which supports the findings of volumetric studies. Both groups of MRS studies support a neuro-developmental hypothesis of brain dysfunction in schizophrenia. However, current methodological problems limit the reliable interpretation of MRS data. A clear understanding of the methodology and its reliable interpretation is yet to emerge. CONCLUSIONS: MRS remains a research instrument that is yet to be fully utilised in schizophrenia research. A few replicated findings are emerging, although the interpretation of these spectroscopic findings needs to be validated.

Brain↗

PubMed2000

Issues associated with the identification of cognitive change following coronary artery bypass grafting.

OBJECTIVE: Coronary artery bypass grafting (CABG) is a surgical procedure used to treat individuals with ischaemic heart disease and to relieve angina. Disruption to the central nervous system (CNS) has frequently been reported by patients who have undergone CABG. METHOD: The following paper is a review of the literature that has examined the effects of CABG on the CNS. RESULTS AND CONCLUSIONS: It becomes apparent that issues about the incidence and severity of post-CABG cognitive decline are still unresolved. First, the cause of post-CABG CNS change has not yet been established, although the presence of changes to brain microvasculature as a result of the presence of microemboli appears to be a likely factor. Second, while some studies have reported high rates of poor performance on neuropsychological tests postoperatively, these reports are often subject to confounds such as variability in postoperative testing intervals, the definition of decline and the neuropsychological test batteries used. Finally, improvements in surgical techniques and changes in patient characteristics may have changed the real nature and prevalence of post-CABG cognitive decline. The review finishes with a series of recommendations for the neuropsychological study of CABG.

Cardiopulmonary Bypass↗

PubMed1999

Attentional modulation of implicit processing of information in spatial neglect.

Patients with parietal lesions often fail to identify stimuli in the contralesional field (i.e. neglect) but may nevertheless demonstrate implicit processing of neglected stimuli. Explanations of implicit processing in neglect range from intact preattentive mechanisms, to intact higher level categorical processing. Such theories assume implicit processing in neglect is passive and not subject to attentional modulation. We investigated implicit processing in a neglect patient US) using a flanker task in which targets differed on two dimensions simultaneously (i.e. coloured letters). Controls demonstrated interference effects only from goal-relevant dimensions of flankers. JS showed a similar pattern of results even when flankers appeared in his neglected field, suggesting that implicit processing of neglected stimuli can be modulated by behavioural goals.

Aged↗

PubMed1999

Asymmetries between dominant and non-dominant hands in real and imagined motor task performance.

Motor imagery is a dynamic state in which an individual mentally simulates the performance of a specific motor action or motor task. Recent behavioural and neuroimaging evidence suggests that the same neurocognitive networks control real and imagined movements. This hypothesis was tested by investigating whether motor asymmetries related to cerebral dominance also occurred for imagined movements. Fifty subjects performed the visually guided pointing task of Sirigu et al. [Sirigu, A., Duhamel, J., Cohen, L., Pillon, B., Dubois, B. and Agid, Y., The mental representation of hand movements after parietal cortex damage. Science, 1996, 273, 1564-1567.] using their dominant and non-dominant hands. Analysis of group data indicated that both real and imagined movement conformed to Fitts' law. Analysis of individual data indicated that asymmetries arising from motor dominance in real movements also occurred for imagined movements. However, the relative slowing and error associated with the non-dominant hand was greater for imagined movements than for real movements. These asymmetries support the hypothesis that real and imagined movements are represented within the same neurocognitive networks but suggest that asymmetries in performance related to handedness are greater for imagined movements. In addition, while the visually guided pointing task provides a useful test of the ability to make imagined movements, asymmetries in the speed and reliability of imagined performance are significantly greater than those for real performance.

Adolescent↗

PubMed1999

Facilitation and inhibition arising from the exogenous orienting of covert attention depends on the temporal properties of spatial cues and targets.

On the covert orienting of visual attention task (COVAT), responses to targets appearing at the location indicated by a non-predictive spatial cue are faster than responses to targets appearing at uncued locations when stimulus onset asynchrony (SOA) is less than approximately 200 ms. For longer SOAs, this pattern reverses and RTs to targets appearing at uncued locations become faster than RTs to targets appearing at the cued location. This facilitation followed by inhibition has been termed the biphasic effect of non-predictive peripheral spatial cues. Currently, there is debate about whether these two processes are independent. This issue was addressed in a series of experiments where the temporal overlap between the peripheral cue and target was manipulated at both short and long SOAs. Results showed that facilitation was present only when the SOA was short and there was temporal overlap between cue and target. Conversely, inhibition occurred only when the SOA was long and there was no temporal overlap between cue and target. The biphasic effect, with an early facilitation followed by a later inhibition, occurred only when the cue duration was fixed such that there was temporal overlap between the cue and target at short but not long SOAs. In a final experiment, the duration of targets the temporal overlap between cue and target and the SOA were manipulated factorially. The results showed that facilitation occurred only when the SOA was short, there was temporal overlap between cue and target and the target remained visible until the subject responded. These results suggest that the facilitation and inhibition found on COVATs which use non-informative peripheral cues are independent processes and their presence and magnitude is related to the temporal properties of cues and targets.

Adult↗

PubMed1999

Abnormalities of imaged motor sequences in children with developmental coordination disorder.

The chronometry of real and imagined movements was investigated in a group of children with developmental coordination disorder (DCD) and a group of matched controls. The visually-guided pointing task was used to investigate the speed for accuracy trade-offs that occur as target size is varied for both real and imagined performance. In the control group, the speed for accuracy trade-off for both real and imagined performance conformed to Fitts' law. In the DCD group only real movements conformed to Fitts' law. This pattern of performance suggests that children with DCD have an impairment in the ability to generate internal representations of volitional movements. This may reflect part of a general impairment in the processing of efference copy in DCD.

Analysis of Variance↗

PubMed1999

Executive function and attention deficit hyperactivity disorder: stimulant medication and better executive function performance in children.

BACKGROUND: Executive function deficits have been reported repeatedly in children with Attention Deficit Hyperactivity Disorder (ADHD). Stimulant medication has been shown to be effective in improving cognitive performance on most executive function tasks, but neuropsychological tests of executive function in this population have yielded inconsistent results. Methodological limitations may explain these inconsistencies. This study aimed to measure executive function in medicated and non-medicated children with ADHD by using a computerized battery, the Cambridge Neuropsychological Test Automated Battery (CANTAB), which is sensitive to executive function deficits in older patients with frontostriatal neurological impairments. METHODS: Executive function was assessed in 30 children with ADHD: 15 were stimulant medication naive and 15 were treated with stimulant medication. These two groups were compared to 15 age, sex and IQ matched controls. RESULTS: The unmedicated children with ADHD displayed specific cognitive impairments on executive function tasks of spatial short-term memory, spatial working memory, set-shifting ability and planning ability. Impairments were also seen on spatial recognition memory and delayed matching to sample, while pattern recognition memory remained intact. The medicated children with ADHD were not impaired on any of the above executive function tasks except for deficits in spatial recognition memory. CONCLUSIONS: ADHD is associated with deficits in executive function. Stimulant medication is associated with better executive function performance. Prospective follow-up studies are required to examine these effects.

Adolescent↗

PubMed1999

Impairment of olfactory identification in obsessive-compulsive disorder.

BACKGROUND: Olfactory identification ability has been associated with processing in the orbitofrontal cortex (OFC), an area that has been implicated in the pathophysiology of obsessive-compulsive disorder (OCD). Although olfactory sensitivity is normal in patients with OCD, no study has investigated olfactory identification in this disorder. METHODS: A group of 20 subjects with OCD and 23 age- and education-matched controls performed a standardized test of olfactory identification. They also performed computerized tests of spatial memory span, spatial working memory and spatial recognition memory that have been shown previously to be sensitive to cognitive deficits in patients with OCD. RESULTS: Performance on the olfactory identification task, spatial recognition task and spatial span task was significantly worse in the OCD group than controls. CONCLUSIONS: While impairment in spatial cognition is consistent with previous studies of OCD, its significance for brain-behaviour models of OCD is unclear. However, the finding of abnormal olfactory identification in patients with OCD is consistent with the hypothesis that there is a disruption to processing at the level of the OFC in the disorder.

Adult↗

PubMed1999

Abnormalities of internally generated saccades in obsessive-compulsive disorder.

BACKGROUND: We aimed to utilize tests of saccadic function to investigate whether cognitive abnormalities in obsessive-compulsive disorder (OCD) arise from a dysfunction of inhibitory processes or whether they reflect a more general difficulty in guiding behaviour on the basis of an internal representation of task goal. METHODS: Twelve patients with OCD and 12 matched controls performed a visually-guided saccade task, a volitional prosaccade task and an antisaccade task. The latency and gain of saccades was compared between groups for the three saccade tasks. The number of antisaccade errors was also calculated and compared between groups. RESULTS: There was no difference for antisaccade error rates between the groups. The latency of visually guided saccades did not differ between groups, however the latency of both volitional prosaccades and antisaccades was significantly slower in the patients with OCD than in controls. The difference in latency between volitional prosacades and antisaccades, however, was equal between groups. CONCLUSIONS: These results suggest that patients with OCD have an abnormality in guiding behaviour on the basis of an internal representation of the task goal, rather than a problem with inhibiting reflexive behaviour.

Adult↗

PubMed1999

Norms and the effects of demographic variables on a neuropsychological battery for use in healthy ageing Australian populations.

OBJECTIVE: The current study examined the performance of a healthy ageing population on the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) neuropsychological test battery in order to determine norms for use in an Australian setting. The effects of age, education, gender and mood on cognitive performance in healthy older individuals were also explored. METHOD: The CERAD neuropsychological battery was administered to a sample of healthy elderly subjects (n = 243). Subjects also completed an anxiety inventory and a depression scale. Means and standard deviations of different age, gender and education groups are reported as normative data. A Principal Components Analysis (PCA) was also calculated. Linear regression was applied to the five factors extracted from the PCA using age, education, gender and mood as independent variables. RESULTS: All recorded means were within 1 SD of those reported in the original CERAD normative study. Five factors that loaded on measures of memory and learning, language, praxis and executive function were extracted. The independent variables age, education and gender all had significant effects on cognitive performance. However, mood had no such effect. CONCLUSIONS: Risk factors for cognitive decline indicated by the CERAD battery include age, education and gender. Anxiety and depression are not associated with CERAD cognitive performance. The CERAD battery is a valid and reliable neuropsychological tool that may assist in the detection and diagnosis of Alzheimer's disease in Australian populations.

Adult↗

PubMed1999

The effects of age and mood on saccadic function in older individuals.

To investigate the effect of age and mood on saccadic function, we recorded prosaccades, predictive saccades, and antisaccades from 238 cognitively normal, physically healthy volunteers aged 44 to 85 years old. Mood levels were measured using the State-Trait Anxiety Inventory and Center for Epidemiological Studies Depression Scale inventories. Small, but significant, positive relationships with age were observed for the mean latency and associated variability of latency for all types of saccades, as well as the antisaccade error rate. Saccade velocity or accuracy was unaffected by age. Increasing levels of depression had a minor negative influence on the antisaccade latency, whereas increasing levels of anxiety raised the antisaccade error rate marginally.

Adult↗

PubMed1999

Covert orienting of visual spatial attention in attention deficit hyperactivity disorder: does comorbidity make a difference?

Attentional performance in children with attention deficit hyperactivity disorder (ADHD) with and without comorbid disorders was examined using the Covert Orienting of Visuospatial Attention Task (COVAT) and the Continuous Performance Task (CPT). The relationship between these two tasks was also examined. The results showed no overall differences on the attention tasks between children with ADHD alone and those with ADHD plus other disorders. Compared to non-ADHD control children, children with ADHD showed a deficit in the disengage operation of covert visuospatial attention, suggesting a difficulty in the endogenous mode of orienting. The ADHD children also showed a general performance deficit on the CPT. Although there was a general slowing on both attention tasks in the ADHD group, there was no relationship between invalid cue effect sizes on the COVAT and the CPT measures. These results indicate that these two attention tasks may be tapping both similar and independent underlying cognitive processes in ADHD.

Journal Article↗

PubMed1998

Investigating form and colour perception in blindsight using an interference task.

Patients with striate cortical damage causing a hemianopic field defect can nevertheless demonstrate residual visual capacities in their blind field. Previous research investigating blindsight required patients to respond explicitly to stimuli appearing in the blind field by making forced choice judgements. We present data from a patient with a left occipital lesion resulting in a homonymous hemianopia, using the flanker task. This patient displayed a significant flanker congruency effect (FCE) for colour and letter stimuli even when they appeared in the blind field. A control patient with a lesion of the right thalamus showed no FCE in the blind field. This suggests that thalamo-extrastriate neural pathways are necessary for residual functioning in blindsight.

Aged↗

PubMed1998

Cognitive deficits in obsessive-compulsive disorder on tests of frontal-striatal function.

BACKGROUND: Although neuropsychological and neuroimaging studies of obsessive-compulsive disorder (OCD) have implicated the frontal cortex and subcortical structures in the pathophysiology of the disorder, few studies have examined cognitive function in patients with OCD on tasks validated in the assessment of frontal lobe and subcortical dysfunction. METHODS: The accuracy and latency of executive and visual memory function was assessed in 23 nondepressed OCD patients and 23 normal healthy controls matched for age, sex, education, and estimated IQ. RESULTS: The patients with OCD performed within the normal range on tasks of short-term memory capacity, delay dependent visual memory, pattern recognition, attentional shifting, and planning ability; however, specific cognitive deficits related to spatial working memory, spatial recognition, and motor initiation and execution were observed in the patient group. These deficits were not correlated with aspects of the patients' intellectual functioning or comorbid psychological symptoms, suggesting that the impairments were related to the specific clinical features of OCD. CONCLUSIONS: Patients with OCD showed specific cognitive deficits on tasks of executive and visual memory function. The pattern of impaired performance in these patients was qualitatively similar to the performance of patients with frontal lobe excisions and subcortical pathology on the same test battery, suggesting that the underlying pathophysiology of the disorder could best be conceptualized as reflecting dysfunction of frontal-striatal systems.

Adult↗