Performance monitoring and executive control of attention in euthymic bipolar disorder: Employing the CPT-AX paradigm

Reduced cognitive test performance has been demonstrated in patients with bipolar disorder (BD), even when euthymic. Several studies have explored aspects of attention, including sustained attention, and reported patients show lower accuracy compared to controls. It is necessary to modify existing attentional paradigms to fully characterise such deficits. The present study sought to examine if there are changes in the profile of performance and error-types during a sustained attention task in BD. Twenty-two euthymic patients with DSM-IV diagnosed BD and 21 healthy controls were recruited. Participants completed a modified CPT-AX paradigm with a high proportion of target trials (70%) with cues and probes presented at continuous intervals. This modification increases the demands on response inhibition and permits the deconstruction of attentional/executive deficits previously described. Overall, BD patients showed significantly poorer target discriminability compared to controls. In block one (first quarter) of the task, patients showed no significant differences to controls, but by the final fourth block (last quarter) they made significantly fewer hits and more errors (both ‘AX’ misses and ‘BX’ false alarms). BD patients completed initial stages of the task similarly to controls, but as demands on the attentional system continued difficulties emerged, consistent with problems in context-maintenance.     

Role of attentional resources on gait performance in Huntington's disease

Patients with Huntington's disease (HD) suffer from cognitive deficits with impaired executive functions, including limited attentional resources. We sought to use a dual‐task paradigm to evaluate attentional demands and the ability of patients with HD to concentrate on two tasks simultaneously. We analyzed the interference effects of cognitive and motor tasks on walking in HD and the contribution of clinical symptoms to gait disturbances. Patients and controls were asked to perform either a motor task (carrying a tray with four glasses), a cognitive task (counting backwards), or no task at all while walking at their preferred speed. Kinematic spatial parameters, temporal parameters, and angular parameters related to gait were recorded in 15 patients and 15 controls by means of a videomotion analysis system. Gait instability was assessed using the stride‐to‐stride variability of the various gait parameters. For patients with HD, performing a concurrent cognitive task resulted in a lower gait speed (compared with free walking), with decreased cadence and stride length. However, this effect was not observed in controls. Performing a motor task did not change any kinematic gait parameters in either HD or control subjects. We found correlations between gait speed in the dual cognitive/walking task on one hand and the motor UHDRS score, cognitive status and executive function on the other. Patients with HD had greater difficulty walking while performing a concurrent cognitive task; the drain on attentional resources deteriorated walking performance. © 2007 Movement Disorder Society     

Concurrent performance of motor tasks and processing capacity in patients with schizophrenia

Any task is carried out more successfully if we allocate undivided attention to it, but as demands on attentional capacity increase-for example, in concurrent or dual task conditions-performance on attended tasks becomes more impaired. Patients with schizophrenia show impaired performance on tasks requiring high levels of attentional capacity. This study examines performance of 11 patients with schizophrenia and 13 normal controls on two motor tasks (placing pegs in a pegboard and repetitive index finger tapping) under unimanual, bimanual, and dual task conditions. The patients with schizophrenia placed fewer pegs and had reduced tapping speed in unimanual and bimanual conditions. However, the decrement in bimanual performance as a percentage of unimanual performance was not significantly different for the patients and controls on either the pegboard or tapping tasks. By contrast, under dual task conditions, the performance of the patients with schizophrenia in peg placement actually improved relative to the unimanual pegboard task, whereas tapping performance deteriorated compared with the unimanual tapping, a decrement that was significantly greater for the patients. Thus the improvement in the visually guided pegboard task was at the expense of the repetitive tapping task. These results are discussed in terms of an impairment of self initiated movement with general sparing of externally triggered movements in schizophrenia and the role of frontostriatal loops in this process.     

Dual-task interference during initial learning of a new motor task results from competition for the same brain areas

Cerebral patterns of activity elicited by dual-task performance throughout the learning of a complex bimanual coordination pattern were addressed. Subjects (N = 12) were trained on the coordination pattern and scanned using fMRI at early (PRE) and late (POST) learning stages. During scanning, the coordination pattern was performed either as a single task or in concurrence with a simultaneous visual search task (i.e. dual task). Kinematics data revealed a significant performance improvement as a result of learning. In PRE-scanning, the dual-task condition induced deterioration of motor performance, relative to the single-task condition. Activity in lateral frontal and parietal regions involved in both visual search and motor coordination tasks (i.e. ‘overlapping’ regions) was reduced when the tasks were performed simultaneously. In POST-scanning, kinematics performance was equivalent under single- and dual-task conditions, suggesting automaticity of the coordination pattern. Furthermore, overlap between regions involved in visual search and motor tasks was reduced, and dual-task performance was no longer associated with reduction of frontal and parietal activity. Our results suggest that behavioral interference between a complex motor coordination task and a simple simultaneous visual search task occurs when both tasks recruit overlapping regions in the frontal and parietal cortices. This may provide a neural basis for dissipation of dual-task interference following extensive motor practice, which is a traditional behavioral marker of motor automaticity.     

Characterization of cognitive and motor performance during dual-tasking in healthy older adults and patients with Parkinson’s disease

The primary purpose of this study was to investigate the effect of dual-tasking on cognitive performance and gait parameters in patients with idiopathic Parkinson’s disease (PD) without dementia. The impact of cognitive task complexity on cognition and walking was also examined. Eighteen patients with PD (ages 53–88, 10 women; Hoehn and Yahr stage I-II) and 18 older adults (ages 61–84; 10 women) completed two neuropsychological measures of executive function/attention (the Stroop Test and Wisconsin Card Sorting Test). Cognitive performance and gait parameters related to functional mobility of stride were measured under single (cognitive task only) and dual-task (cognitive task during walking) conditions with different levels of difficulty and different types of stimuli. In addition, dual-task cognitive costs were calculated. Although cognitive performance showed no significant difference between controls and PD patients during single or dual-tasking conditions, only the patients had a decrease in cognitive performance during walking. Gait parameters of patients differed significantly from controls at single and dual-task conditions, indicating that patients gave priority to gait while cognitive performance suffered. Dual-task cognitive costs of patients increased with task complexity, reaching significantly higher values then controls in the arithmetic task, which was correlated with scores on executive function/attention (Stroop Color-Word Page). Baseline motor functioning and task executive/attentional load affect the performance of cognitive tasks of PD patients while walking. These findings provide insight into the functional strategies used by PD patients in the initial phases of the disease to manage dual-task interference.     

Aging,executive control,and attention: a review of meta-analyses

We review the results of a series of meta-analyses by the first author and colleagues, examining age-related differences in selective attention (Stroop-task survey and negative-priming task survey) and in divided attention (dual-task survey and task-switching survey). The four task families all lent themselves to state trace analysis, in which performance in baseline conditions was contrasted with performance in experimental conditions separately for college-aged subjects and for elderly subjects. These analyses found no age-related deficits specific to selective attention or local task-switching. Age deficits were found for dual-task performance and global task-switching. Unlike selective attention and local task-switching costs, dual-task and global task-switching costs were found to be additive in both young and old subjects, unmodulated by task difficulty. These forms of executive intervention then did not alter computational processes already present in the simple tasks, but rather added one or more additional processing steps or stages to the processing stream. The cost was greater in older adults, but was limited to those experimental conditions that activated multiple task sets.     

Dual-task conditions modulate the efficiency of selective attention mechanisms in Alzheimer's disease

Given previous demonstrations of both selective and divided attention deficits in Alzheimer's disease (AD) patients, understanding how declines in the integrity of component processes of selective attention in these patients interact with impairments to executive processes mediating dual-task performance has both theoretical and practical relevance. To address this issue, healthy elderly and AD patients performed computerized tasks of spatial orienting, Simon response interference, and visual search both in isolation and while simultaneously engaged in a visuomotor tracking task (i.e., maintaining car position within a simulated driving environment). Results from the single-task conditions confirmed previous demonstrations of selective attention deficits in AD. Dual-task conditions produced in AD patients (but not healthy elderly) a change in the efficiency of the selective attention mechanisms themselves, as reflected in differential effects on cue or display conditions within each task. Rather than exacerbating the selective attention deficits observed under single-task conditions, however, dual-task conditions produced an apparent diminution of these deficits. We suggest this diminution is due to the combination of deficient top-down inhibitory processes along with a decrease in the attention-capturing properties of cue information under dual-task conditions in AD patients. These findings not only increase our understanding of the nature of the attentional deficits in AD patients, but also have implications for understanding the processes mediating attention in neurologically intact individuals.     

The contribution of executive functions deficits to impaired episodic memory in individuals with alcoholism

Individuals with alcoholism commonly exhibit impaired performance on episodic memory tasks. However, the contribution of their impaired executive functioning to poor episodic memory remains to be clarified. Thirty-six recently detoxified and sober asymptomatic alcoholic men and 36 matched non-alcoholic participants were tested for processing speed, prepotent response inhibition, mental flexibility, coordination of dual-task and a verbal episodic memory task. Compared with non-alcoholic individuals, the alcoholic patients showed impaired executive functions combined with below normal performance on both free and delayed recall. In contrast, processing speed, cued recall and recognition were preserved. Regression analyses revealed that 47% of alcoholics' episodic memory's free recall performance was predicted by mental flexibility and that 49% of their delayed recall performance was predicted by mental flexibility, manipulation of dual-task and prepotent response inhibition. Regarding participants' executive predictors of episodic memory performance, the slopes of β coefficients were significantly different between the two groups, with alcoholics requiring more their executive system than non-alcoholics. Once detoxified, alcoholic patients showed episodic memory deficits mainly characterized by impaired effortful (executive) processes. Compared with controls, patients used effortful learning strategies, which are nonetheless less efficient.     

Control of attention in schizophrenia

The deficits of attention contribute significantly to the clinical picture of functional disability seen in schizophrenia, but there is no consensus as to whether this cognitive function can be fractionated to allow further characterisation of the impairment. We examined fifteen patients with chronic schizophrenia and fifteen controls using paired tasks designed to measure four hypothetical aspects of attentional control: the ability to focus attention, to resist distraction, to shift attention, and to divide attention. The group with schizophrenia showed a significant improvement in accuracy on a digit span repetition task when a simultaneous box-crossing task was added (divided attention condition). Although the patient group showed impaired performance across nearly all of the tasks, they were not disproportionately impaired during the task conditions assumed to demand greater attention. These results suggest that the aspects of attention and executive function under study are not significantly affected by schizophrenia and indicate the need for further characterisation of the impairment usually reported using conventional tests of attention on those with schizophrenia.     

Increased attentional demands impair contralesional space awareness following stroke

Rate and severity of contralesional loss of awareness following stroke is highly variable across patients and assessment methods. We studied whether the degree of impairment for contralesional space awareness depends on the quantity of attentional resources that are available for task performance. A new computer-based paradigm was used to assess visual extinction and single-target detection rate in four right hemisphere stroke patients. In the single-task condition, they had to report only the position of the target(s) (“right”, “left”, or “both” sides). In the dual-task conditions, patients also performed a second task, visual or auditory, that recruited additional attentional resources. The same tasks were also performed by healthy controls and by a left hemisphere stroke patient. Patients’ performance was apparently unimpaired in the single-task condition. In contrast, dramatic failures to report the left-sided target emerged in the dual-task conditions. The performance of control participants was unaffected by the dual-task manipulation, whereas the left stroke patient showed the opposite pattern (i.e., unawareness of right-sided targets). Severe contralesional space unawareness under dual-task conditions reveals that visuospatial deficits can dramatically emerge when attentional resources are consumed by a concurrent task. Apparently spared contralesional awareness may simply reflect the availability of resources that are just sufficient to perform a single-task. This finding has important implications for the assessment of contralesional space awareness following stroke, because everyday life activities are often more demanding than most of the tests adopted for diagnosing space awareness disorders.     

Dual-task performance in early stage dementia: differential effects for automatized and effortful processing

Attentional functions of individuals with early stage Alzheimer's disease (AD) and normal older adults (NC) were studied using a concurrent-task paradigm. Fourteen patients (5 men, 9 women) and 14 age- and sex-matched normal adults engaged in speeded unimanual tapping and speaking tasks during single- and dual-task trials. Speaking tasks were either relatively automatized (Speech Repetition) or relatively effortful (Speech Fluency). As single-task tapping rates were slower for the AD participants than for the NC participants, a proportional decrement score was used as an index of interference in the dual-task conditions. Interference during concurrent-task performance was greater when the cognitive task was effortful for both the NC and the AD groups. Although AD patients suffered higher levels of interference than NC participants while performing the effortful speech task, the two groups showed equivalent small changes in tapping speed while combining the automatized speaking and tapping tasks. Results suggest that a general-purpose attentional processing resource declines in the early stages of AD but dual-task performance is well-maintained when the component tasks are relatively automatized.     

Visual search patterns in neglect: Comparison of peripersonal and extrapersonal space

Previous studies of visual search patterns in visuospatial neglect have analyzed shifts of attention during search tasks using eye tracking technology and verbal reports. The purpose of the present study was to replicate and extend upon reported parameters of visual scanning patterns of neglect patients in peripersonal space (within arms reach) and to examine whether similar patterns of visual search are also apparent in extrapersonal space (beyond arms reach). Using a simple verbal visual search and target detection paradigm right-hemisphere stroke participants, with and without neglect, and healthy older volunteers named targets on scanning sheets placed in peripersonal and extrapersonal space. The healthy controls and right-hemisphere stroke group without neglect showed similar ‘reading’ type strategies, while the neglect group displayed an unsystematic search pattern, during search in both peripersonal and extrapersonal space. Group comparisons of search parameters support the presence of multiple cognitive deficits affecting the complex visual search patterns of neglect patients, including a rightward attentional bias, a reduced spatial scale of attention (local processing bias), and a deficit of working memory affecting both near and far space search. Ventral visual stream damage and neglect, however, were related to slower target report rate and more misidentification errors in extrapersonal space. The ease of administration of this verbal target detection task in both peripersonal and extrapersonal space, and the relationship of the measures produced to theorized attentional and executive deficits in neglect, provide impetus for further research on the severity and independence of individual scanning deficits in neglect.     

Effects of divided attention on episodic memory in chronic traumatic brain injury: a function of severity and strategy

Eleven patients with mild traumatic brain injury (MTBI) and 13 patients with moderate-to-severe TBI (STBI) were compared to 10 matched controls on episodic memory for pictorial scene–object associations (e.g. kitchen–bread) and a range of standardized neuropsychological tests of memory and frontal-lobe functions. We tested the hypothesis that deficits in episodic memory result from impaired attentional resources and/or strategic control by manipulating attentional load at encoding (focused versus divided attention) and environmental support at retrieval (free recall and recalled cued by scene versus recognition of object and scene). Patients with TBI were disproportionately affected by the divided attention manipulation, but this effect was modulated by injury severity and encoding strategy. Overall, MTBI patients were impaired only when items were encoded under divided attention, indicating memory deficits that were secondary to deficits in the executive control. STBI patients could be differentiated into two distinct functional subgroups based on whether they favored a strategy of attending to the encoding or digit-monitoring task. The subgroup favoring the digit-monitoring task demonstrated deficits in the focused attention condition, and disproportionate memory deficits in the divided attention condition. In contrast, the subgroup favoring the encoding task demonstrated intact performance across all memory measures, regardless of attentional load, and despite remarkable similarity to the other STBI subgroup on demographic, neuropsychological, and acute injury severity measures. We discuss these outcome differences in terms of the relationship between strategy and executive control and highlight the need for more sensitive anatomical and behavioral measurement at both acute and chronic stages of injury.     

Deficits in inhibitory executive functions in Klinefelter (47, XXY) syndrome

Klinefelter syndrome (47, XXY) is a sex chromosome aneuploidy associated with mild deficits in cognitive and language functions. Dysfunctions have also been reported in performance of tasks which examine executive functions. However, it is unclear whether the impaired performance is caused or accentuated by problems with semantic processing and information processing speed. In the present study we used an experimental task which is relatively insensitive to these confounding factors. We examined inhibitory executive functions in a group of XXY males compared with male (XY) and female (XX) controls, using a dichotic listening speech sound task with instructions to focus attention on either the right or the left ear stimulus. With this task, inhibitory executive functions can be assessed separately from language, processing speed, and attention orientation abilities. We found that XXY males showed a selective deficit in inhibitory executive functions compared to both control groups, whereas attentional orientation was not impaired. The present findings suggest that executive dysfunctions associated to Klinefelter syndrome can be selectively identified, and are particularly accentuated in the inhibitory sub-component. Such improved understanding of the nature of executive dysfunctions in XXY males may aid the development of specific neuropsychological rehabilitation strategies.     

Dual-task performance in depressed geriatric patients.

Older patients suffering from a major depression are often impaired on tasks that require executive control processes. However, a wide variety of executive abilities exist in humans, and it is not clear that all are impaired in depression or that such impairments persist beyond remission of the depression. One executive process that plays a central role in mental operations such as working memory is the ability to co-ordinate the simultaneous performance of multiple tasks. Dual-task performance has been extensively studied in normal subjects but there is little work with depressed patients. The present study examined the performance of depressed (M age=71.0, S.D.=7.1) and control subjects (M age=69.3, S.D.=7.0) on two tasks (visual tracking and backward digit span), both when each task was carried out by itself and when the two tasks were carried out simultaneously. Dual-task performance was impaired in depressed patients prior to antidepressant treatment and this impairment persisted even after remission of the depression. These results suggest that, like other executive abilities, the ability to schedule and co-ordinate the conflicting processing demands present in a dual-task situation is impaired in depressed geriatric patients and that this impairment may be a trait effect.     

Greater impairment of ability in the divided attention task is seen in Alzheimer's disease patients with depression than in those without depression

BACKGROUND: Recent studies have emphasized specific deficits of attention and executive functions, such as those of cognitive flexibility, divided attention, in geriatric patients with depression. In Alzheimer's disease (AD), depressive symptoms are known to occur even from an early stage of the disease. However, the nature of the impairment of executive functions in depression associated with AD remains unclear, because of the frequent occurrence of the apathy syndrome as a major confounding factor. METHOD: In this study, we conducted a comprehensive comparative neuropsychological assessment in AD patients with (n=21) and without (n=21) depression. The diagnosis of depression was based on provisional criteria proposed by Olin's group. RESULTS: In terms of apathy symptoms, both groups had a similar degree of deficits, which were mild as assessed according to Neuropsychiatric Inventory criteria. While no significant differences were observed in regard to the scores in general intellectual functioning, episodic memory and some attention and executive tasks between the two groups, AD patients with depression showed significantly lower scores in several attention and executive function tasks, such as the dual-task performance task administered to assess the capacity for divided attention, and the cognitive flexibility (Trail Making Test; Part B), than AD patients without depression. CONCLUSIONS: Our results suggest that depressive symptoms in AD patients increase the deficits of cognitive flexibility and divided attention. This is the first study to report a correlation between depressions, diagnosed based on the provisional criteria for depression in AD by Olin's group, and an impaired capacity for divided attention in AD patients.     

The pattern of attentional deficits in Parkinson's disease

BackgroundCognitive impairment without dementia is frequent in Parkinson's disease. It often presents as a dysexecutive syndrome with deficient attentional resource allocation. The nature of attention deficits in Parkinson's disease has rarely been investigated with robust, theory-based tasks. The main objective of the present study was to investigate attention disorders in Parkinson's disease patients by applying a paradigm based on a model of attention. We also sought to identify the main demographic and clinical characteristics associated with attention deficits in Parkinson's disease.MethodsEighty non-demented Parkinson's disease patients and 60 healthy controls participated in the study. Attention was assessed in a computer-controlled reaction time paradigm. The test session comprised a simple reaction time task and four choice reaction time tasks: a go/no-go task, a one-dimension, focused-attention task, a two-dimension, divided-attention task and an alternating task. Performance was assessed by composite measures: (i) cognitive reaction time, corresponding to the difference between the simple reaction time and the choice reaction time in the given condition, and (ii) reaction time variability, corresponding to the sum of the coefficients of variance of the reaction times. Accuracy was also considered.ResultsApart from an overall slowing and greater reaction time variability, Parkinson's disease patients were only significantly impaired in the alternating condition. This set-shifting impairment was associated with their performance in the go/no-go and divided-attention conditions.ConclusionOur systematic assessment of the different attentional subcomponents revealed that mental flexibility is particularly impaired in non-demented Parkinson's disease patients.     

Cognitive dysfunction in non-demented Parkinson's disease patients: Controlled and automatic behavior

The evidence with regard to impaired automatic and controlled information processing in non-demented patients with Parkinson's disease (PD) is critically discussed. We use a comprehensive mental schema framework of executive functioning, that is the planning and regulation of behavior in complex everyday tasks (International Classification of Functioning - ICF - activity level).In this framework monitoring, inhibition, mental effort, planning, working memory and flexibility are important elements of controlled processing (supervisory attentional control) and controlled processing can only influence performance by modulating automatic processes. The striatum plays an important role in the interface between controlled and automatic processes.It is wel documented that PD patients show impairments applying and achieving automaticities. With sustained cortical control of task performance during both automatic and controlled processing, not showing the transition to striatal control, which is normal in the case of skill learning.In addition, PD patients have been shown to be limited in executive functioning. Many authors have interpreted this as evidence for impaired executive functions (ICF body level). But the question must be asked to what extent these limitations are an indirect effect of impaired automatic processing. To answer this question, studies on executive functioning are critically assessed with regard to the control they have provided for impaired automaticity.It is concluded that only for cognitive flexibility and working memory, the evidence for impairments is convincing because significant limitations have also been shown in tasks with very low automatic processing demands. Impairments in other executive functions, such as monitoring, inhibition and planning have not been convincingly shown in non-demented PD patients and are likely to be due to treatment strategies and factors such as fatigue.     

Divided attention and mental effort after severe traumatic brain injury

The aim of this study was to assess dual-task performance in TBI patients, under different experimental conditions, with or without explicit emphasis on one of two tasks. Results were compared with measurement of the subjective mental effort required to perform each task. Forty-three severe TBI patients at the subacute or chronic phase performed two tasks under single- and dual-task conditions: (a) random generation; (b) visual go-no go reaction time task. Three dual-task conditions were given, requiring either to consider both tasks as equally important or to focus preferentially on one of them. Patients were compared to matched controls. Subjective mental effort was rated on a visual analogic scale. TBI patients showed a disproportionate increase in reaction time in the go-no go task under the dual-task condition. However, they were just as able as controls to adapt performance to the specific instructions about the task to be emphasised. Patients reported significantly higher subjective mental effort, but the variation of mental effort according to task condition was similar to that of controls. These results suggest that the divided attention deficit of TBI patients is related to a reduction in available processing resources rather than an impairment of strategic processes responsible for attentional allocation and switching. The higher level of subjective mental effort may explain why TBI patients frequently complain of mental fatigue, although this subjective complaint seems to be relatively independent of cognitive impairment.     

Neuropsychological functioning and alcohol dependence

PURPOSE OF REVIEW: Alcohol dependence is a significant challenge to society and health-care services. The associated cognitive deficits are thought to affect behavioral control, therapy and liability to relapse. The present review demonstrates important new findings. RECENT FINDINGS: Recent interest focused on compensatory functional circuits, components of executive functioning, externally induced attentional biases and the relevance of the cognitive deficits for therapy and rehabilitation. SUMMARY: Recent studies found widespread compromised fronto-cortico-cerebellar circuits to underlie cognitive deficits. The inclusion of cerebellar structures to support functions traditionally associated with cortical and even prefrontal structures is important. However, most importantly, alcohol-dependent patients use additional and generally higher-order executive functions to compensate for deficient task performance. The compensatory mechanisms might help to explain close to normal functioning in basic cognitive domains enabled by support of executive components. But deficits in executive functions themselves might emerge more directly. New approaches concerning executive functioning, analyzing functional components of executive tasks, found response inhibition and decision-making to be impaired but normal performance in simple working memory tasks.Multiple withdrawals have been shown to lead to a higher degree of executive deficit. The causing mechanism underlying the attentional bias induced by alcohol-related words (stroop effect) is still under debate. Correlation of cognitive deficits with therapy outcome turned out to be weak. However, important interactions of cognitive deficits with personality, therapy-setting and successful coping, together with the finding that cognitive performance of alcohol-dependent patients could be enhanced by motivating instructions, might open new strategies in treatment planning and cognitive rehabilitation.