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Ian H Robertson

Publications and source records attributed to Ian H Robertson.

At least 37 records · Page 2Linked to original sources
PubMed2006

Cognitive rehabilitation interventions for neglect and related disorders: moving from bench to bedside in stroke patients.

The spatial neglect syndrome, defined by asymmetric attention and action not attributed to primary motor or sensory dysfunction and accompanied by functional disability, is a major cause of post-stroke morbidity. In this review, we consider the challenges and obstacles facing scientific researches wishing to evaluate the mechanisms and effectiveness of rehabilitation interventions. Spatial neglect is a heterogeneous disorder, for which consensus research definitions are not currently available, and it is unclear which of the deficits associated with the syndrome causes subsequent disability. We review current opinion about methods of assessment, suggest a rational approach to selecting therapies which requires further study, and make systems-level and theoretical recommendations for building theory. We lastly review some creative questions for consideration in future research.

Animals↗
PubMed2005

Capture by misleading information and its false acceptance in patients with traumatic brain injury.

Exposure to misleading information, presented after a critical episode, can alter or impair memory reports about that episode. Here, we examine vulnerability to misleading information in patients with traumatic brain injury (TBI). The ability to initiate an effective retrieval strategy and inhibit irrelevant or interfering information requires participation from the prefrontal cortices, which are susceptible to damage following brain injury. We report that TBI patients are more prone to interference effects produced by misleading information during a cued-recall task and are more likely to accept this information as the product of 'remembering' compared with healthy controls. The results are consistent with a model proposing that patients are captured by highly accessible responses eliminating their opportunity to engage in recollection. Correlations between the cued-recall interference task and other executive measures helped elucidate the processes underlying 'capture'. In TBI patients, reduced recollection produced by a misleading prime was associated with impaired prospective remembering when engaged in a background task. A common functional deficit that may underlie poor performance on both tasks is the failure to inhibit previously relevant but currently irrelevant information. Subjective reports pertaining to the subject's cued-recall response were indexed by electrodermal activity. In control subjects, larger skin conductance responses (SCRs) were associated with a greater frequency of guess reports, suggesting that SCRs provide a marker for uncertainty regarding the candidacy of a selected response. TBI patients did not show this relationship, suggesting that impairments of post-retrieval evaluation might also underlie greater false acceptance of misinformation. Discussion focuses on the role of the prefrontal cortex and cognitive processes that mediate the selection and evaluation of memories.

Adult↗
PubMed2005

Sustained attention in traumatic brain injury (TBI) and healthy controls: enhanced sensitivity with dual-task load.

Poor sustained attention or alertness is a common consequence of traumatic brain injury (TBI) and has a considerable impact on the recovery and adjustment of TBI patients. Here, we describe the development of a sensitive laboratory task in healthy subjects (Experiment 1) and its enhanced sensitivity to sustained attention errors in TBI patients (Experiment 2). The task involves withholding a key press to an infrequent no-go target embedded within a predictable sequence of numbers (primary goal) and detecting grey-coloured targets within the sequence (secondary goal). In Experiment 1, we report that neurologically healthy subjects are more likely to experience a lapse of attention and neglect the primary task goal, despite ceiling performance on the secondary task. Further, attentional lapses on the task correlated with everyday attentional failures and variability of response time. In Experiment 2, the task discriminates between TBI patients and controls with a large effect size. The dual-task yields more errors in both groups than a simple task involving only the primary goal that is commonly used to detect sustained attention deficits in neurologically impaired groups. TBI patients' errors also correlated with everyday cognitive failures and variability of response time. This was not the case in the simple version of the task. We conclude that the dual-task demand associated with this task enhances its sensitivity as a measure of sustained attention in TBI patients and neurologically healthy controls that relates to everyday slips of attention.

Adult↗
PubMed2005

DRD4 gene variants and sustained attention in attention deficit hyperactivity disorder (ADHD): effects of associated alleles at the VNTR and -521 SNP.

Associations between attention deficit hyperactivity disorder (ADHD) and genetic variants within the dopamine D4 receptor gene have been much reported. Variants investigated include the 7-repeat allele of a VNTR within the third exon, and two SNPs (-521 and -616) located with the promoter region. We investigated the relationship between the VNTR, -521, and -616 SNPs and sustained attention performance in 54 ADHD probands, relative to a non-genotyped control group. Participants performed the Sustained Attention to Response Task (SART) in which the response to an unpredictably occurring target digit must be inhibited. This task, therefore, challenged sustained attention and included a response inhibition component. Consistent with previous reports, ADHD participants possessing the 7-repeat allele of the VNTR outperformed those children not possessing this allele, both in terms of errors and response variability. In family based analyses, better performance on the SART tended to predict biased transmission of the 7-repeat allele from heterozygous parents. For the -521 SNP, A allele homozygotes showed greater impairment than heterozygotes or those not possessing this allele, both in terms of total errors and response variability. Family based analysis showed that higher total errors on the SART predicted transmission of the A allele from heterozygous parents. There were no effects of the -616 SNP. Our results suggest dissociable effects of the "associated alleles" of DRD4 gene variants on sustained attention: while the 7-repeat allele of the VNTR is associated with relatively better performance, the A allele of the -521 SNP is associated with poorer performance.

Adolescent↗
PubMed2005

The methionine allele of the COMT polymorphism impairs prefrontal cognition in children and adolescents with ADHD.

ADHD is a highly heritable psychiatric disorder of childhood. A functional polymorphism (Val158Met) of the catechol-O-methyltransferase (COMT) gene has attracted interest as a candidate gene for ADHD. The high-activity valine variant of this polymorphism degrades prefrontal dopamine three to four times more quickly than the low-activity methionine variant and could therefore contribute to the proposed hypodopaminergic state in ADHD. Here we tested for association of this polymorphism with ADHD and examined its influence on prefrontal cognition in ADHD. We have previously reported no association of the Val158Met COMT gene polymorphism in 94 Irish ADHD families (Hawi et al. (2000) Am J Med Genet 96:282-284). Here we re-examined this finding with an extended sample of 179 ADHD cases using a family control design. We also examined the performance of children and adolescents with ADHD (n = 61) on a standardised test of sustained attention. Analysis confirmed the absence of an association between the Val158Met COMT gene polymorphism and the clinical phenotype of ADHD. COMT genotype, however, affected prefrontal cognition in ADHD: ADHD children who were homozygous for the valine variant had significantly better sustained attention than those ADHD children possessing at least one copy of the methionine variant. Children possessing the methionine variant performed significantly below age-related norms on tests of sustained attention. Contrary to expectations, the methionine variant of the Val158Met COMT gene polymorphism impaired prefrontally-mediated cognition in ADHD. This effect may be understood by positing a hyper-functioning of prefrontal dopaminergic systems. Against this background, the slower clearance of dopamine associated with the methionine variant of the COMT gene polymorphism may be disadvantageous to cognition in ADHD.

Adolescent↗
PubMed2005

Repetitive behaviour in Alzheimer's disease: description, correlates and functions.

BACKGROUND: Repetitive behaviour is among the most common and burdensome of the behavioural and psychological symptoms of Alzheimer's disease (AD), yet little research has been done to investigate its nature or correlates. Memory impairment may account for repetitive questioning, but its possible role in other repetitive behaviours is unclear. Attention and executive dysfunction may account for both repetitive speech and actions. The role of mood also merits investigation. OBJECTIVES: To investigate cognitive and affective differences between patients with and without repetitive behaviours, and to identify themes and carer attributions for the function of such behaviours. METHODS: Fifty-four participants aged > or = 65, meeting NINCDS-ADRDA criteria for probable AD, were assessed using the MMSE, WMS-III word list, Trailmaking test, Stroop, Modified WCST, Cornell Scale for Depression, DEX and a repetitive behaviour questionnaire. Regression analyses were used to identify significant predictors of repetitive behaviour. RESULTS: Repetitive behaviours were manifest in 87% of the sample, with questions (68.5%) and statements/stories (61.1%) the most common types. Repetitive questions were predicted by high MMSE score (p = 0.013), low immediate list recall score (p = 0.013) and female gender (p = 0.004). Repetitive statements/stories were predicted by dysexecutiveness (p = 0.003) and younger age (p = 0.016). Repetitive actions were predicted by longer illness duration (p = 0.041), depressive symptoms (p = 0.035) and dysexecutiveness (p < 0.001). Themes and patterns were evident in repetitive behaviour. CONCLUSIONS: Repetitive behaviours were common in a sample of patients with AD referred to hospital clinics. Vocal and motor repetitive behaviours were predicted by different cognitive, demographic and mood variables.

Affect↗
PubMed2005

Neurophysiological markers of alert responding during goal-directed behavior: a high-density electrical mapping study.

The ability to dynamically modulate the intensity of sustained attention (i.e., alertness) is an essential component of the human executive control system, allowing us to function purposefully in accordance with our goals. In this study we examine high-density ERP markers of alert responding during the fixed sequence sustained attention to response task (SART(fixed)). This paradigm has proven to be a sensitive clinical metric in patient populations with deficits in their ability to sustain attention (e.g., attention deficit hyperactivity disorder). In this task subjects withhold a button press to an infrequent no-go target ('3') embedded within a predictable sequence of numbers ('1' to '9'). Our data reveal a complex pattern of effects across the trial sequence of the SART, with clear contributions from frontal and parietal cortices to sustained attentional performance. Over occipito-parietal regions, early visual attention processes were increased during trial 2 (i.e., trial in which the digit '2' was presented) and trial 3, giving rise to the so-called selection negativity (SN). Two prominent late components were manifest during trial 2: LP1 (550-800 ms) and LP2 (850-1150 ms) over occipito-parietal and central sites. We interpret the LP1 component on trial 2 as reflecting retrieval of the task goal and the subsequent LP2 as reflecting competition between the currently relevant go response and the subsequent no-go response. On trial 3, an enhanced "no-go N2" (250-450 ms) was seen fronto-centrally in the absence of the "no-go P3" that typically follows. Fronto-polar activity was also seen across all trials and may be indicative of subgoal processes to integrate the association between stimulus and goal. Prior to a lapse of attention (i.e., failure to inhibit a response to "3") the LP1 was significantly attenuated on the preceding trial 2 indicating a failure of anticipatory goal-directed processing. The results are discussed in terms of models of sustained attention involving frontal and parietal cortices.

Adolescent↗
PubMed2005

Dissecting the attention deficit hyperactivity disorder (ADHD) phenotype: sustained attention, response variability and spatial attentional asymmetries in relation to dopamine transporter (DAT1) genotype.

ADHD is a childhood-onset behavioural disorder with a heterogeneous profile of neuropsychological impairment. Neuropsychological heterogeneity may, in part, reflect underlying genetic differences. Here we examined sustained attention, response variability and spatial attentional asymmetries in a sample of children and adolescents with ADHD (n=22) in relation to dopamine transporter genotype (DAT1) and also controls (n=20). Participants performed the sustained attention to response task (SART) (testing sustained attention and response variability) and the greyscales task (a perceptual measure of attentional bias). The latter has previously been shown to yield a robust leftward attentional asymmetry in healthy subjects. The 10-repeat allele of the DAT1 gene has been associated with ADHD in a number of studies and appears to have biological significance. The ADHD group was sub-divided into those individuals with two copies of the "high-risk" 10-repeat allele (high-risk DAT1) versus those with one or no copies of this allele (low-risk DAT1). The high-risk DAT1 ADHD group displayed greater response variability on the SART than either the low-risk DAT1 group or healthy controls, whereas the latter two groups did not differ. Further, the high-risk DAT1 group showed an attenuated spatial asymmetry, relative to the low-risk DAT1 ADHD group, who showed the typical leftward attentional asymmetry. Our results suggest that the 10-repeat DAT1 allele may mediate neuropsychological impairment in ADHD. The application of molecular genetics may help to define neuropsychological impaired subgroups of ADHD.

Adolescent↗
PubMed2005

Association between dopamine transporter (DAT1) genotype, left-sided inattention, and an enhanced response to methylphenidate in attention-deficit hyperactivity disorder.

A polymorphism of the dopamine transporter gene (DAT1, 10-repeat) is associated with attention-deficit hyperactivity disorder (ADHD) and has been linked to an enhanced response to methylphenidate (MPH). One aspect of the attention deficit in ADHD includes a subtle inattention to left space, resembling that seen after right cerebral hemisphere damage. Since left-sided inattention in ADHD may resolve when treated with MPH, we asked whether left-sided inattention in ADHD was related to DAT1 genotype and the therapeutic efficacy of MPH. A total of 43 ADHD children and their parents were genotyped for the DAT1 3' variable number of tandem repeats polymorphism. The children performed the Landmark Test, a well-validated measure yielding a spatial attentional asymmetry index (leftward to rightward attentional bias). Parents rated their child's response to MPH retrospectively using a three-point scale (no, mediocre or very good response). Additionally, parents used a symptom checklist to rate behavior while on and off medication. A within-family control design determined whether asymmetry indices predicted biased transmission of 10-repeat parental DAT1 alleles and/or response to MPH. It was found that left-sided inattention predicted transmission of the 10-repeat allele from parents to probands and was associated with the severity of ADHD symptomatology. Children rated as achieving a very good response to MPH displayed left-sided inattention, while those rated as achieving a poorer response did not. Our results suggest a subgroup of children with ADHD for whom the 10-repeat DAT1 allele is associated with left-sided inattention. MPH may be most efficacious in this group because it ameliorates a DAT1-mediated hypodopaminergic state.

Adolescent↗
PubMed2005

Impaired sustained attention and error awareness in traumatic brain injury: implications for insight.

The processes of error awareness and sustained attention were investigated in 18 traumatic brain injury (TBI) individuals and 16 matched control participants. In Experiment 1, we found that: (1) in comparison to controls, TBI participants displayed reduced sustained attention and awareness of error during the Sustained Attention to Response Task; (2) degree of error awareness was strongly correlated with sustained attention capacity, even with severity of injury partialed out; and (3) that error feedback significantly reduced errors. We replicated the finding of a correlation between error awareness and sustained attention capacity in Experiment 2 with a separate sample of 19 TBI participants and 20 controls. We conclude that TBI leads to impaired sustained attention and error awareness. The finding of a significant relationship between these two deficits in TBI suggests there may be a link between these two processes. Feedback on error improves sustained attention performance of control and TBI participants.

Adolescent↗
PubMed2005

Variability in time reproduction: difference in ADHD combined and inattentive subtypes.

OBJECTIVE: To examine the relationship between time reproduction, performance variability, and sustained attention deficits in children with attention-deficit/hyperactivity disorder (ADHD) combined (ADHD-C) and inattentive (ADHD-I) subtypes, relative to matched controls. METHOD: Participants (age range 7.1-14.1 years) performed a time reproduction task. A subset of the ADHD group was also tested on the Sustained Attention to Response Test. Absolute discrepancy, accuracy coefficient, and intraindividual variability scores on the time reproduction task were compared across the three groups (ADHD-C: N = 20; ADHD-I: N = 19; controls: N = 44) and correlated with the Sustained Attention to Response Test. RESULTS: First, significantly better performance was observed in matched controls than in children with ADHD on the time reproduction task. Second, there was a significant difference between the two ADHD subtypes in the variability of the size of errors made at high time intervals (36-60 seconds). Third, intraindividual performance variability in the direction (over- versus underestimations) of time reproductions correlated with sustained attention performance. CONCLUSIONS: Children with ADHD varied more in the size and direction of their time reproduction errors than control children. Those with ADHD-C demonstrated more intraindividual variability than did those with ADHD-I in the size of their errors. The data provide support for a relationship between sustained attention and time reproduction. This relationship has previously been inferred from common right-lateralized neural circuitry that is thought to subserve these processes.

Adolescent↗
PubMed2005

Are the cognitive deficits associated with impaired insight in schizophrenia specific to executive task performance?

Although impaired insight in schizophrenia has been associated with deficits in executive task performance, the relationship remains unclear. We aimed to clarify this relationship by fractionating executive functioning into the theoretically derived functions of inhibition, working memory, set shifting, and sustained attention. We compared the performance of patients showing impaired insight, patients showing good insight, and a matched control group on measures of each of these executive functions, along with measures of current cognitive functioning and memory. We found that while patients with impaired insight performed significantly below those with good insight on our working memory task, they also performed poorly on measures of general cognitive functioning and memory. We conclude that while impaired insight does appear to be associated with executive deficits, this association may not be specific but may instead relate to cognitive deficits more generally.

Adult↗
PubMed2004

Reduced electrodermal response to errors predicts poor sustained attention performance in attention deficit hyperactivity disorder.

Research into attention deficit hyperactivity disorder (ADHD) has indicated abnormalities in electrodermal system activity (EDA) and separately, deficits in sustained attention. Here we asked whether reduced EDA in ADHD was consequential for the attention problems associated with this disorder. On a sustained attention task ADHD participants had higher overall error rates and exhibited a marked decrease in skin conductance responses (SCRs) to errors, relative to control children. Further, sustained attention errors were predicted by SCR amplitudes. Evidence of post-error slowing in both groups suggested comparable error awareness. It is proposed that attenuation of the normal autonomic response to errors reflects impairment in ADHD participants' psychological response to error significance and results in decreased behavioural correction and hence poorer sustained attention.

Analysis of Variance↗
PubMed2004

EEG alpha power changes reflect response inhibition deficits after traumatic brain injury (TBI) in humans.

Brain damage due to traumatic brain injury (TBI) has been associated with deficits in executive functions and the dynamic control of behaviour. Event-related brain potentials and spectral power data were recorded from eight TBI participants and eight matched controls while they completed a Go/NoGo response inhibition task. The TBI group was found to be significantly impaired at the task compared to controls, and exhibited abnormal N2 and P3 waveform components in response to NoGo stimuli relative to controls. Significant correlations were also found between alpha power, Go-trial RT and errors. We conclude that abnormal activity in the structures damaged in this group may render such patients less capable of maintaining a state of alpha desynchronisation compared to controls, resulting in poorer performance on the task.

Adult↗
PubMed2004

Attenuation of spatial attentional asymmetries with poor sustained attention.

The co-existence of deficits in sustained and spatial attention in patients with acquired damage to the right cerebral hemisphere has led to the proposition that sustained attention could be a marker for left spatial inattention, or neglect. We investigated the possibility that reductions in leftward spatial attentional asymmetries could arise from individual differences in the capacity for sustained attention even within healthy adult populations. We observed that healthy participants who performed poorly on a test of sustained attention had a significantly attenuated left spatial bias, relative to those with good sustained attention capacity, on a free-viewing spatial attention test. Our results provide further support for the notion that sustained attention may exert a modulatory influence on spatial attention.

Adult↗
PubMed2004

Behavioural and physiological impairments of sustained attention after traumatic brain injury.

Sustaining attention under conditions of low external demand taxes our ability to stay on task and to avoid more appealing trains of thought or environmental distractions. By contrast, a stimulating, novel environment engages attention far more freely without the subjective feeling of having to override monotony. Our ability to maintain a goal-directed focus without support from the environment requires the endogenous control of behaviour. This control can be modulated by fronto-parietal circuits and this ability is compromised following traumatic brain injury (TBI) leading to increased lapses of attention. In this paper, we further explore a laboratory paradigm that we argue is particularly sensitive to sustained attention as opposed to other aspects of attentional control involving the selection and management of goals in working memory. The paradigm (fixed sequence Sustained Attention to Response Task--SARTfixed) involves withholding a key press to an infrequent no-go target embedded within a predictable sequence of numbers. We demonstrate that TBI patients in this study make disproportionately more errors than controls on this task. An analysis of response times (RTs) and EEG alpha power across the task demonstrates group differences preceding the critical no-go trial. Controls demonstrate a lengthening of RTs accompanied by desynchronization of power within the alpha band (approximately 10 Hz) preceding the no-go trial. Conversely, the TBI group showed a shortening of RTs during this period with no evidence of alpha desynchronization. These findings suggest that TBI patients may have dysfunctional alpha generators as a consequence of their injury that impairs endogenous control during the task.

Adult↗
PubMed2004

Poor insight in traumatic brain injury mediated by impaired error processing? Evidence from electrodermal activity.

Impaired deficit awareness is common following traumatic brain injury (TBI) and is a major obstacle to rehabilitation. We have previously confirmed the presence of impaired error awareness in TBI using a highly discriminating go/no-go procedure. In the present study, we extend this work to try to identify more closely the nature of the error awareness deficit using measures of electrodermal activity (EDA). Sixteen participants with TBI and sixteen age-, sex-, and education-matched controls performed the Sustained Attention to Response Task (SART), while EDA was recorded. TBI detected significantly fewer errors compared to controls. EDA was significantly attenuated for TBI participants even to errors of which they were aware; error detection rates and EDA amplitude were also correlated. These findings suggest that poor insight following TBI may result, in part, from impaired error processing abilities.

Adult↗