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Biomedical subjects

J Currie

Publications and source records attributed to J Currie.

At least 19 recordsLinked to original sources
PubMed2002

Frontal atrophy correlates with behavioural changes in progressive supranuclear palsy.

Regional brain volumes were measured in 21 patients with progressive supranuclear palsy (PSP), 17 patients with Parkinson's disease and 23 controls using 3D MRI-based volumetry. Cortical, subcortical and ventricular volume measures were correlated with global indices of motor disability and cognitive disturbance. All MRI measures, including hippocampal volume, were preserved in Parkinson's disease. Patients with PSP could be distinguished from both Parkinson's disease and controls by whole brain volume loss, ventricular dilatation and disproportionate atrophy of the frontal cortex. Caudate nucleus volume loss additionally differentiated PSP from controls, but was modest in severity and proportionate to whole brain volume loss. The present study identifies disease-specific differences in the topography of brain atrophy between PSP and Parkinson's disease, and has potential implications for the in vivo radiological differentiation of these two disorders. In PSP, the variance in frontal grey matter volume related to measures of behavioural disturbance, confirming the use of behavioural tests for ante-mortem case differentiation and suggesting that intrinsic cortical deficits contribute to these clinical disturbances.

Aged↗
PubMed2001

Contextual abnormalities of saccadic inhibition in children with attention deficit hyperactivity disorder.

Abnormalities of executive function are observed consistently in children with attention-deficit hyperactivity disorder (ADHD), and it is hypothesised that these arise because of disruption to a behavioural inhibition system. Executive and inhibitory functions were compared between unmedicated and medicated children with ADHD (combined type), age-matched healthy children and healthy adults. Executive functions were measured using a test of spatial working memory shown previously to be sensitive to ADHD and to stimulant medication. Inhibitory functions were measured using an ocular motor paradigm that required individuals to use task context to control the release of fixation. Context was set according to the probability that a target would appear at either of the two locations. In one block, targets appeared on 80% of trials. In the other block, targets appeared on 20% of trials. The ability to control the release of fixation was inferred from the fixation offset effect (FOE), or the difference in saccade latency when the current fixation is offset 200 ms prior to the onset of the saccade target (gap condition), compared with when there is no offset (overlap condition). Although the healthy children made more errors on the spatial working memory task than the healthy adults, there was no difference between the two groups in their ability to control fixation using context. Both showed a larger FOE when target probability was low. As expected, the unmedicated ADHD group made more errors on the spatial working memory test than the healthy children, although spatial working memory performance was normal in the medicated ADHD group. However, both the unmedicated and medicated ADHD groups were unable to modulate the FOE according to context, and this was due to their inability to voluntarily inhibit saccades when there was a low target probability. These data suggest that the context-based modulation of fixation release is not controlled by the same systems that control executive function. Furthermore, deficits in executive function and inhibitory control appear independent in children with ADHD.

Attention Deficit Disorder with Hyperactivity↗
PubMed2001

Responses of magnocellular neurons to osmotic stimulation involves coactivation of excitatory and inhibitory input: an experimental and theoretical analysis.

How does a neuron, challenged by an increase in synaptic input, display a response that is independent of the initial level of activity? Here we show that both oxytocin and vasopressin cells in the supraoptic nucleus of normal rats respond to intravenous infusions of hypertonic saline with gradual, linear increases in discharge rate. In hyponatremic rats, oxytocin and vasopressin cells also responded linearly to intravenous infusions of hypertonic saline but with much lower slopes. The linearity of response was surprising, given both the expected nonlinearity of neuronal behavior and the nonlinearity of the oxytocin secretory response to such infusions. We show that a simple computational model can reproduce these responses well, but only if it is assumed that hypertonic infusions coactivate excitatory and inhibitory synaptic inputs. This hypothesis was tested first by applying the GABA(A) antagonist bicuculline to the dendritic zone of the supraoptic nucleus by microdialysis. During local blockade of GABA inputs, the response of oxytocin cells to hypertonic infusion was greatly enhanced. We then went on to directly measure GABA release in the supraoptic nucleus during hypertonic infusion, confirming the predicted rise. Together, the results suggest that hypertonic infusions lead to coactivation of excitatory and inhibitory inputs and that this coactivation may confer appropriate characteristics on the output behavior of oxytocin cells. The nonlinearity of oxytocin secretion that accompanies the linear increase in oxytocin cell firing rate reflects frequency-facilitation of stimulus-secretion coupling at the neurohypophysis.

Animals↗
PubMed2001

Memory decline in healthy older people: implications for identifying mild cognitive impairment.

BACKGROUND: Criteria for mild cognitive impairment require objective evidence of a memory deficit but do not require objective evidence of memory decline. Application of these criteria may therefore result in the misclassification of older patients with memory decline as normal because their neuropsychological test performance at a single point in time may be within normal limits. This study aimed to identify and characterize older people with memory decline. METHOD: Word list delayed recall (WLDR) test performance was assessed on five occasions during a 2-year period in a cohort of healthy older individuals. Older people with declining (n = 35) and nondeclining (n = 66) WLDR scores were identified. Both subgroups were then compared on apoE genotype, Clinical Dementia Rating, and neuropsychological test performance at the fifth assessment. RESULTS: Thirty-four percent of the group with declining memory recorded a Clinical Dementia Rating of 0.5, compared with 5% of the nondeclining memory group. No between-group differences were observed in cognitive domains other than memory, self-reported cognitive failures, or the proportion of each group carrying the apoE epsilon 4 allele. CONCLUSIONS: A large proportion of healthy older individuals show memory decline, which may represent the early stages of a potentially more severe cognitive impairment. Further investigation is necessary to determine the relationship between apoE genotype, self-reported cognitive impairment, and memory decline in older people.

Aged↗
PubMed2001

The ability to execute saccades on the basis of efference copy: impairments in double-step saccade performance in children with developmental co-ordination disorder.

The double-step saccade task (DSST) was used to test the hypothesis that children with developmental co-ordination disorder (DCD) who experience deficits in motor imagery have difficulty processing the visual spatial consequences of intended movements using efference copy signals. In order to ensure that the second saccade in the DSST was executed in the absence of visual cues and had to be programmed on the basis of extra-retinal information (efference copy), we analysed only those double-step ensembles where latency plus duration of first saccades was greater than 240 ms (total presentation time of the targets). No significant differences between DCD and control children were evident on measures of latency of first saccades, intersaccadic interval and first saccade error. As predicted, children with DCD who have impaired motor imagery demonstrated specific deficits on the DSST where efference copy had been used to program the saccade sequence. More specifically, these children were less accurate in terms of final eye position on second saccades. Our results raise the possibility that abnormalities in the processing of efference copy signals could underlie motor clumsiness in the majority of children with DCD. Furthermore, the origin of this deficit in efference copy probably exists at the level of the parietal lobe.

Child↗
PubMed2001

Abnormalities of motor and praxis imagery in children with DCD.

In an earlier study using the visually guided pointing task (VGPT) the authors showed that the timing of imagined movement sequences in children with developmental coordination disorder (DCD) does not conform to the conventional speed-for-accuracy trade-off (or Fitts' law [P.M. Fitts, Journal of Experimental Psychology 47 (1954) 381-391]) that occurs when the distance and accuracy requirements of movements are varied [P. Maruff, P.H. Wilson, M. Trebilcock, J. Currie, Neuropsychologia 37 (1999b) 1317-1324]. The present study sought to replicate this earlier finding and to examine (using a weight manipulation) whether this deficit was also attributable to inaccurate programming of relative force. The chronometry of real and imagined movements was investigated in a group of 20 children with DCD aged between 8 and 12 years and a group of controls matched on age and verbal IQ (VIQ). Movement duration was tested for real and imagined movements using the preferred hand, with the VGPT performed under two load conditions: with and without the addition of a weight attached to a pen. Group means of each subjects' mean movement duration were calculated and plotted against target width for each of the four conditions [Movement type (2) x Load (2)] and a logarithmic curve was fitted to the data points. In the control group, the speed-for-accuracy trade-off for both real and imagined performance conformed to Fitts' law under each load condition. In the DCD group only real movements conformed to Fitts' law. Moreover, the effect of load differed between groups--for real movements, movement duration did not differ between load and no-load conditions for either group, while for imagined movements, movement duration increased under the load condition for the control group only. These results replicate and extend the results of our earlier study. This pattern of performance suggests that children with DCD have an impairment in the ability to generate internal representations of volitional movements which may reflect an impaired ability to process efference copy signals. The ability to programme both relative force and timing appears to underly this difficulty. Results have implications for the use of (guided) motor imagery training in order to facilitate the development of motor skill in children with DCD.

Child↗
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

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

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↗