Dual task performance after severe diffuse traumatic brain injury or vascular prefrontal damage

Fiber Connectivity Density in Cerebral Small-Vessel Disease Patients With Mild Cognitive Impairment and Cerebral Small-Vessel Disease Patients With Normal Cognition

Abnormal structural connectivity of cerebral small-vessel disease (CSVD) is associated with cognitive impairment. But the different characteristics of structural connectivity have not been elucidated in early CSVD patients. The current study aimed to investigate the potential differences of structural connectivity in CSVD patients with mild cognitive impairment (MCI) and CSVD patients with normal cognition. Twenty-two CSVD patients with MCI, 34 CSVD patients with normal cognition, and 35 controls, who were age, sex, and education matched underwent diffusion tensor imaging and high resolution T1-weighted imaging. Clinical characteristics, lacunar infarct volume, white matter hyperintensity (WMH) volume, and global atrophy were quantitatively evaluated. Maps of fiber connectivity density (FiCD) were constructed and compared across groups in vertex levels. Pearson correlation was used to estimate the imaging–clinical relationships with control of general characteristics. CSVD patients with MCI had higher lesion load of WMH and lacunar infarcts, and correspondingly lower global FiCD value than CSVD patients with normal cognition (P < 0.01). Lacunar infarct (r = −0.318, P < 0.01) and WMH (r = −0.400, P < 0.01), but not global atrophy, age, or sex, were significantly correlated with the global FiCD value. CSVD patients with normal cognition showed decreased FiCD value mainly in the prefrontal areas (P < 0.01 with Monte Carlo correction). Compared with CSVD patients with normal cognition, CSVD patients with MCI showed significantly decreased FiCD value in enlarged frontal and parietal areas (P < 0.01 with Monte Carlo correction). Inter-group comparisons showed regional enhanced impairment of connectivity density in CSVD patients with MCI in the left superior frontal gyrus, the left precuneus, and the orbital part of the right inferior frontal gyrus (P < 0.01 with Monte Carlo correction). Regional FiCD value of frontal and parietal areas was associated with the cognitive function (P < 0.01). In conclusion, cognitively normal CSVD patients already have disruptions of structural connectivity. The extent and intensity of connectivity disruptions in frontal and parietal areas may underlie the mechanism of cognitive impairment in CSVD. Fiber connectivity density measurements may be helpful for quantitative description of structural cortical connectivity.

The Causal Role of the Lateral Prefrontal Cortex for Task-order Coordination in Dual-task Situations: A Study with Transcranial Magnetic Stimulation

Dual tasks are characterized by the requirement for additional task-order coordination processes that schedule the processing order of two temporally overlapping tasks. Preliminary evidence from functional imaging studies suggests that lateral pFC (lPFC) activation correlates with implementing these task-order coordination processes. However, so far, it is unclear whether the lPFC is also causally involved in coordinating task order during dual-task performance and which exact mechanisms are implemented by this brain region. In this study, we addressed these open issues by applying online TMS during a dual-task situation. For this purpose, participants performed a dual task in fixed-order blocks with a constant order of tasks and in random-order block, in which the order of tasks varied randomly and thus demands on task-order coordination were increased. In Experiment 1, TMS of the lPFC compared with control TMS conditions impaired dual-task performance in random-order blocks, whereas performance in fixed-order blocks was unaffected by TMS. In Experiment 2, we tested for the specificity of the lPFC TMS effect on task-order coordination by applying TMS over the preSMA. We showed that preSMA TMS did not affect dual-task performance, neither in fixed-order nor in random-order blocks. Results of this study indicate that the lPFC, but not the preSMA, is causally involved in implementing task-order coordination processes in dual-task situations.

Saccadic impairment in chronic traumatic brain injury: examining the influence of cognitive load and injury severity

OBJECTIVE

Previous research suggests that saccadic eye movements can be uniquely sensitive to impairment in chronic traumatic brain injury (TBI). This study was conducted to examine saccadic eye movements across varying levels of cognitive load and TBI history/severity. We hypothesized that saccadic impairment in chronic mild and moderate-severe TBI would be most pronounced under conditions of high cognitive load.

METHODS

In total, 61 participants (including n = 20 with chronic mild TBI, n = 15 with chronic moderate-severe TBI, and 26 uninjured controls) completed a battery of conventional neuropsychological tests and the Fusion n-Back Test, which measures manual and saccadic response time (RT) across varying cognitive load and cueing conditions.

RESULTS

Consistent with our hypotheses, chronic mild and moderate-severe TBI were associated with substantial saccadic impairment under conditions of high cognitive load. Participants with moderate-severe TBI also demonstrated saccadic impairment at low levels of cognitive load. TBI groups and uninjured controls did not differ significantly on manual metrics or conventional neuropsychological measures.

CONCLUSIONS

This study provides additional support for the value of eye tracking for enhanced assessment of TBI. Additionally, findings suggest that TBI is associated with greatest susceptibility to oculomotor interference under high levels of cognitive load.

Neuropsychology of traumatic brain injury: An expert overview

Traumatic brain injury (TBI) is a serious healthcare problem, and this report is a selective review of recent findings on the epidemiology, pathophysiology and neuropsychological impairments following TBI. Patients who survive moderate-to-severe TBI frequently suffer from a wide range of cognitive deficits and behavioral changes due to diffuse axonal injury. These deficits include slowed information-processing and impaired long-term memory, attention, working memory, executive function, social cognition and self-awareness. Mental fatigue is frequently also associated and can exacerbate the consequences of neuropsychological deficits. Personality and behavioral changes can include combinations of impulsivity and apathy. Even mild TBI raises specific problems: while most patients recover within a few weeks or months, a minority of patients may suffer from long-lasting symptoms (post-concussion syndrome). The pathophysiology of such persistent problems remains a subject of debate, but seems to be due to both injury-related and non-injury-related factors.

Randomised controlled trial of the efficacy of a blue-enriched light intervention to improve alertness and performance in night shift workers

OBJECTIVES

Night workers often experience high levels of sleepiness due to misalignment of the sleep-wake cycle from the circadian pacemaker, in addition to acute and chronic sleep loss. Exposure to light, in particular short wavelength light, can improve alertness and neurobehavioural performance. This randomised controlled trial examined the efficacy of blue-enriched polychromatic light to improve alertness and neurobehavioural performance in night workers.

DESIGN

Participants were 71 night shift workers (42 males; 32.8±10.5 years) who worked at least 6 hours between 22:00 and 08:00 hours. Sleep-wake logs and wrist actigraphy were collected for 1-3 weeks, followed by 48-hour urine collection to measure the circadian 6-sulphatoxymelatonin (aMT6s) rhythm. On the night following at least two consecutive night shifts, workers attended a simulated night shift in the laboratory which included subjective and objective assessments of sleepiness and performance. Workers were randomly assigned for exposure to one of two treatment conditions from 23:00 hours to 07:00 hours: blue-enriched white light (17 000 K, 89 lux; n=36) or standard white light (4000 K, 84 lux; n=35).

RESULTS

Subjective and objective sleepiness increased during the night shift in both light conditions (p<0.05, η_p²=0.06-0.31), but no significant effects of light condition were observed. The 17 000 K light, however, did improve subjective sleepiness relative to the 4000 K condition when light exposure coincided with the time of the aMT6s peak (p<0.05, d=0.41-0.60).

CONCLUSION

This study suggests that, while blue-enriched light has potential to improve subjective sleepiness in night shift workers, further research is needed in the selection of light properties to maximise the benefits.

TRIAL REGISTRATION NUMBER

The Australian New Zealand Clinical Trials Registry ACTRN12610000097044 (https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=320845&isReview=true).

Development of modularity in the neural activity of children's brains

We study how modularity of the human brain changes as children develop into adults. Theory suggests that modularity can enhance the response function of a networked system subject to changing external stimuli. Thus, greater cognitive performance might be achieved for more modular neural activity, and modularity might likely increase as children develop. The value of modularity calculated from functional magnetic resonance imaging (fMRI) data is observed to increase during childhood development and peak in young adulthood. Head motion is deconvolved from the fMRI data, and it is shown that the dependence of modularity on age is independent of the magnitude of head motion. A model is presented to illustrate how modularity can provide greater cognitive performance at short times, i.e. task switching. A fitness function is extracted from the model. Quasispecies theory is used to predict how the average modularity evolves with age, illustrating the increase of modularity during development from children to adults that arises from selection for rapid cognitive function in young adults. Experiments exploring the effect of modularity on cognitive performance are suggested. Modularity may be a potential biomarker for injury, rehabilitation, or disease.

Traumatic brain injury and cognition

Traumatic brain injury (TBI) is a major cause of death and disability, and therefore an important health and socioeconomic problem for our society. Individuals surviving from a moderate to severe TBI frequently suffer from long-lasting cognitive deficits. Such deficits include different aspects of cognition such as memory, attention, executive functions, and awareness of their deficits. This chapter presents a review of the main neuropsychological and neuroimaging studies of patients with TBI. These studies found that patients evolve differently according to the severity of the injury, the mechanism causing the injury, and the lesion location. Further research is necessary to develop rehabilitation methods that enhance brain plasticity and recovery after TBI. In this chapter, we summarize current knowledge and controversies, focusing on cognitive sequelae after TBI. Recommendations from the Common Data Elements are provided, with an emphasis on diagnosis, outcome measures, and studies organization to make data more comparable across studies. Final considerations on neuroimaging advances, rehabilitation approaches, and genetics are described in the final section of the chapter.

Evidence of cognitive decline in older adults after remote traumatic brain injury: an exploratory study

Separate bodies of literature indicate that a history of a traumatic brain injury (TBI) and natural aging may result in overlapping cognitive profiles, yet little is known about their combined effect. We predicted that a remote TBI would compound normal age-related cognitive decline, particularly affecting executive function. Neuropsychological task performance was compared between a group of older adults who sustained a TBI in their distant past (N = 9) and a group of older adults with no history of head injury (N = 15). While all participants scored in the normal range on the Mini-Mental State Examination, the TBI group scored lower than the non-TBI group. Also, in line with predictions, the TBI group made more errors on measures of executive functioning compared to the non-TBI group (the Trail Making B test and the incongruent condition of the Stroop Test), but performed similarly on all tasks with little executive requirements. Findings from this exploratory study indicate that a past TBI may put older adults at a higher risk for exacerbated age-related cognitive decline compared to older adults with no history of TBI.

Temporal dysfunction in traumatic brain injury patients: primary or secondary impairment?

Adequate temporal abilities are required for most daily activities. Traumatic brain injury (TBI) patients often present with cognitive dysfunctions, but few studies have investigated temporal impairments associated with TBI. The aim of the present work is to review the existing literature on temporal abilities in TBI patients. Particular attention is given to the involvement of higher cognitive processes in temporal processing in order to determine if any temporal dysfunction observed in TBI patients is due to the disruption of an internal clock or to the dysfunction of general cognitive processes. The results showed that temporal dysfunctions in TBI patients are related to the deficits in cognitive functions involved in temporal processing rather than to a specific impairment of the internal clock. In fact, temporal dysfunctions are observed when the length of temporal intervals exceeds the working memory span or when the temporal tasks require high cognitive functions to be performed. The consistent higher temporal variability observed in TBI patients is a sign of impaired frontally mediated cognitive functions involved in time perception.

Evaluating short-term and working memory in older adults: French normative data

Short-term and working memory (WM) capacities are subject to change with ageing, both in normal older adults and in patients with degenerative or non-degenerative neurological disease. Few normative data are available for comparisons of short-term and WM capacities in the verbal, spatial and visual domains. To provide researchers and clinicians with a set of standardised tasks that assess short-term and WM using verbal and visuospatial materials, and to present normative data for that set of tasks. The present study compiled normative French data for three short-term memory tasks (verbal, visual and spatial simple span tasks) and two WM tasks (verbal and spatial complex span tasks) obtained from 445 healthy older adults aged between 55 and 85 years. Our data reveal main effects of age, education level and gender on older adults' short-term and WM performances. Equation-based normalisation can therefore be used to take these factors into account. The results provide a set of cut-off scores for five standardised tasks that can be used to determine the presence of short-term or WM impairment in older adults.

Neuroimaging correlates of traumatic brain injury and suicidal behavior

INTRODUCTION

There is an urgent need to define the neurobiological and cognitive underpinnings of suicidal ideation and behavior in veterans with traumatic brain injury (TBI). Separate studies implicate frontal white matter systems in the pathophysiology of TBI, suicidality, and impulsivity. We examined the relationship between the integrity of major frontal white matter (WM) systems on measures of impulsivity and suicidality in veterans with TBI.

METHODS

Fifteen male veterans with TBI and 17 matched healthy controls (HC) received clinical ratings, measures of impulsivity and MRI scans on a 3T magnet. Diffusion tensor imaging (DTI) data for the genu and cingulum were analyzed using Freesurfer and FSL. Correlations were performed for fractional anisotropy (FA) (DTI) values and measures of suicidality and impulsivity for veterans with TBI.

RESULTS

Significantly decreased in FA values in the left cingulum (P = 0.02), and left (P = 0.02) and total genu (P = 0.01) were observed in the TBI group relative to controls. Measures of impulsivity were significantly greater for the TBI group and total and right cingulum FA positively correlated with current suicidal ideation and measures of impulsivity (P <0.03).

CONCLUSION

These data demonstrate a significant reduction in FA in frontal WM tracts in veterans with mild TBI that was associated with both impulsivity and suicidality. These findings may reflect a neurobiological vulnerability to suicidal risk related to white matter microstructure.

Conflict adaptation and cognitive control adjustments following traumatic brain injury

Survivors of severe traumatic brain injury (TBI) often demonstrate impairments in the cognitive control functions of detecting response conflict and signaling for recruitment of cognitive resources to appropriately adjust performance. These cognitive control functions can be measured using conflict adaptation effects, wherein manifestations of conflict detection and processing are reduced following high- relative to low-conflict trials. Event-related potentials (ERPs) were collected while 18 survivors of severe traumatic brain injury (TBI) and 21 demographically matched control participants performed a modified Stroop task. The incongruent-minus-congruent trial Stroop effect for trials preceded by incongruent (high conflict) and congruent (low conflict) trials were compared for behavioral (response time [RT] and error rate) and ERP reflections of cognitive control. Behavioral data showed a reduction in the Stroop effect for both control and TBI participant RTs when preceded by incongruent trials. The magnitude of these effects did not differentiate control and TBI participants. ERP data revealed a centro-parietal conflict slow potential (conflict SP) that differentiated incongruent from congruent trials. Planned comparisons showed a decreased amplitude conflict SP when ERPs were preceded by incongruent trials in control, but not TBI participants. Results indicate subtle TBI-related impairments in conflict resolution mechanisms in the context of intact RT-related conflict adaptation.

Evaluating a clinical measure of reaction time: an observational study

The present study was an initial evaluation into the reliability and validity of a novel clinical measure of reaction time that consists of a vertical cylinder that is released and caught as quickly as possible. 65 healthy adults performed clinical and computerized reaction time tasks (RT(clin) and RT(comp)) under simple and dual-task conditions. RT(clin) demonstrated excellent test-retest and interrater reliabilities and was significantly correlated with the criterion standard RT(comp). RT(clin) increased with increasing age and when tested under dual-task conditions. These preliminary results suggest that RT(clin) is a reliable and valid measure of reaction time.

Can measures of cognitive function predict locomotor behaviour in complex environments following a traumatic brain injury?

PRIMARY OBJECTIVE

To determine the relationships between clinical measures of executive function and attention, and laboratory measures of anticipatory locomotor adaptations with dual tasks following a TBI.

METHODS AND PROCEDURES

Ten people with moderate or severe TBI were compared to 10 healthy subjects for neuropsychological measures in the clinic, as well as locomotor patterns and reading time in the laboratory for adapted Stroop tasks (Bar and Word) during unobstructed and obstructed walking.

MAIN OUTCOMES AND RESULTS

As previously found 1 (Vallee M, McFadyen BJ, Swaine B, Doyon J, Cantin JF, Dumas D. Effects of environmental demands on locomotion after traumatic brain injury. Archives of Physical Medicine Rehabilitation 2006;87:806--813) during the locomotor activities, subjects with TBI walked slower, had higher clearance margins and took longer to read during the Stroop tasks than healthy subjects. In general, subjects with TBI also showed deficits in executive functions and attention. Significant relationships were specifically observed between scores on Trail Making B and clearance margins for subjects with TBI, but not for healthy subjects. Alternatively, significant relationships between clinical scores on Stroop and dual task Stroop reading times were obtained for healthy subjects but not for subjects with TBI.

CONCLUSIONS

These results suggest that measures of executive functioning and attention may be associated to locomotor behaviour in complex environments following a moderate to severe TBI.

fMRI study of problem-solving after severe traumatic brain injury

OBJECTIVE

To assess the cerebral correlates of the dysexecutive syndrome after diffuse severe traumatic brain injury (TBI).

METHODS

Ten patients with sub-acute/chronic severe TBI without detectable focal cortical contusion and 11 matched healthy subjects were included in a parametric fMRI study using a planning task, the Tower of London.

RESULTS

Brain activation in the left Dorsolateral Pre-frontal Cortex (DLPFC) and the Anterior Cingulate Cortex (ACC) was closely related to performance. Patients with TBI who performed the task efficiently showed, like healthy controls who obtained a similar pattern of performance, a large activation in the left DLPFC and a small activation in the ACC. In contrast, poor performance was associated with a reduced activation in these both regions.

CONCLUSION

Problem-solving deficits after severe diffuse TBI could be related to an impaired activation of the DLPFC and of the ACC.

Subjective fatigue, mental effort, and attention deficits after severe traumatic brain injury

OBJECTIVE

Although fatigue is one of the most frequent complaints of individuals with traumatic brain injury (TBI), its mechanisms remain poorly understood. The objective of this study was to assess the relationships between subjective mental fatigue, mental effort, attention deficits, and mood after severe TBI.

METHODS

and participants. A total of 27 patients with subacute/chronic severe TBI were compared with matched controls. Patients first rated their baseline subjective fatigue on the Fatigue Severity Scale (FSS) and on the Visual Analog Scale for Fatigue (VAS-F). Mood was assessed with the Montgomery and Asberg Depression Rating Scale (MADRS). Then, they performed a long-duration selective attention task, separated in 2 parts. Fatigue on the VAS-F was assessed again between the 2 parts and at the end of the attention task. Patients were also asked to rate on the VAS the level of subjective mental effort devoted to the task.

RESULTS

Patients reported a higher baseline fatigue than controls. They performed significantly poorer on the selective attention task. Significant correlations were found in the group with TBI between attention performance, mental effort, and subjective fatigue. Depression did not significantly correlate with fatigue.

DISCUSSION AND CONCLUSIONS

These findings suggest that patients with more severe attention deficits have to produce higher levels of mental effort to manage a complex task, which may increase subjective fatigue, in line with the coping hypothesis.

Simple dual tasking recruits prefrontal cortices in chronic severe traumatic brain injury patients, but not in controls

The ability to carry out two tasks simultaneously, dual tasking, is specifically impaired after traumatic brain injury (TBI). The aim of the present study was to investigate the neuronal correlates to this increased dual cost in chronic severe TBI patients (n = 10) compared to healthy controls (n = 11) using functional magnetic resonance imaging (fMRI) at 3 Tesla (T). The tasks were a visual search and a simple two-fingers button press motor task. Performance data demonstrated similar and significant dual task interference in both TBI patients and controls using a linear mixed model. However, principal component analysis showed that TBI patients and controls could be classified into different categories based on motor activity in the single compared to the dual task condition, thus reflecting the increased variability in the performance in the TBI group. Random effects between-group analysis demonstrated significantly reduced activation in the TBI group in both single task conditions in the occipital and posterior cingulate cortices, and for the visual task also in the thalami. This pattern was reversed in the dual task condition with significantly increased activation of a predominantly left lateralized prefrontal-anterior midline-parietal network in the TBI group compared to the controls. The increase in activation occurred within regions described to be engaged in healthy volunteers as dual task cost increases. This finding points to substitution, functional reorganization within the primary network subserving the task, following TBI, and demonstrates more effortful processing. Recruitment of these additional prefrontal resources may be connected to serial rather than parallel processing in low level dual tasking in TBI. Thus, in severe TBI, low level dual task performance depends on increased attentional and executive guidance.

Recollecting, recognizing, and other acts of remembering: an overview of human memory

The question of whether memory is important to human existence is simple to answer: life without memory would be devoid of any meaning. The question of what memory is, however, is much more difficult to answer. The main purpose of this article is to provide an overview of memory function, by drawing distinctions between different memory systems, specifically declarative (ie, conscious) versus nondeclarative (ie, nonconscious) memory systems. To distinguish between these larger systems and their various components, we include discussion of deficits in memory that occur as a consequence of brain injury and normative aging processes. Included in these descriptions is discussion of the neuroanatomical correlates of each memory component described to illustrate the importance of particular brain regions to different aspects of memory function.

Working memory after severe traumatic brain injury

The aim of the present study was to assess the functioning of the different subsystems of working memory after severe traumatic brain injury (TBI). A total of 30 patients with severe chronic TBI and 28 controls received a comprehensive assessment of working memory addressing the phonological loop (forward and backward digit span; word length and phonological similarity effects), the visuospatial sketchpad (forward and backward visual spans), and the central executive (tasks requiring simultaneous storage and processing of information, dual-task processing, working memory updating). Results showed that there were only marginal group differences regarding the functioning of the two slave systems, whereas patients with severe TBI performed significantly poorer than controls on most central executive tasks, particularly on those requiring a high level of controlled processing. These results suggest that severe TBI is associated with an impairment of executive aspects of working memory. The anatomic substrate of this impairment remains to be elucidated. It might be related to a defective activation of a distributed network, including the dorsolateral prefrontal cortex.

Working memory brain activation following severe traumatic brain injury

Functional magnetic resonance imaging (fMRI) has shown that brain activation during performance of working memory (WM) tasks under high memory loads is altered in adults with severe traumatic brain injury (TBI) relative to uninjured subjects (Perlstein et al., 2004; Scheibel et al., 2003). Our study attempted to equate TBI patients and orthopedically injured (OI) subjects on performance of an N-Back task that used faces as stimuli. To minimize confusion in TBI patients that was revealed in pilot work, we presented the memory conditions in two separate tasks, 0- versus 1-back and 0- versus 2-back. In the 0- versus 1-back task, OI subjects activated bilateral frontal areas more extensively than TBI patients, and TBI patients activated posterior regions more extensively than OI subjects. In the 0- versus 2-back task, there were no significant differences between the groups. Analysis of changes in activation over time on 1-back disclosed that OI subjects had decreases in bilateral anterior and posterior regions, while TBI patients showed activation increases in those and other areas over time. In the 2-back condition, both groups showed decreases over time in fusiform and parahippocampal gyri, although the OI group also showed increases over time in frontal, parietal, and temporal areas not seen in the TBI patients. The greatest group differences were found in the 1-back condition, which places low demand on WM. Although the extent of activation in the 2-back condition did not differ between the two groups, deactivation in the 2-back condition was seen in the OI patients only, and both groups' patterns of activation over time varied, suggesting a dissociation between the TBI and OI patients in recruitment of neural areas mediating WM.

The Effect of Moderate to Severe Traumatic Brain Injury (TBI) on Different Aspects of Memory:A Selective Review

Deficient learning and memory are frequently reported as a consequence of traumatic brain injury (TBI). Because of the diffuse nature of the injury, patients with TBI are not the ideal group for studying brain-behavior relations. Nevertheless, characterization of the memory breakdown following TBI could contribute to the assessment and rehabilitation of this patient population. It is well documented that memory is not a unitary system. Accordingly, in this article I review studies that have investigated the long-term effect of moderate to severe TBI on different memory aspects, including explicit and implicit tests of memory. This review demonstrates that TBI affects a large range of memory aspects. One of the conclusions is that the memory impairment observed in TBI patients could be viewed, at least to some degree, as a consequence of a more general cognitive deficit. Thus, unlike patients suffering from global amnesia, memory in patients with TBI is not selectively impaired. Nevertheless, it is possible to detect a subgroup of patients that do meet the criteria of amnesia. However, the most common vulnerable memory processes following TBI very much resemble the memory deficits reported in patients following frontal lobe damage, e.g., difficulties in applying active or effortful strategy in the learning or retrieval process. The suggested similarity between patients with TBI and those suffering from frontal lobe injury should be viewed cautiously; considering the nature of TBI, patients suffering from such injuries are not a homogeneous group. In view of this limitation, the future challenge in this field will be to identify subgroups of patients, either a priori according to a range of factors such as severity of injury, or a posteriori based on their specific memory deficit characteristics. Such a research approach has the potential of explaining much of the variability in findings reported in the literature on the effect of TBI on memory.

Diffusion tensor imaging in the corpus callosum in children after moderate to severe traumatic brain injury

Diffusion tensor imaging (DTI) is a recent imaging technique that assesses the microstructure of the cerebral white matter (WM) based on anisotropic diffusion (i.e., water molecules move faster in parallel to nerve fibers than perpendicular to them). Fractional anisotropy (FA), which ranges from 0 to 1.0, increases with myelination of WM tracts and is sensitive to diffuse axonal injury (DAI) in adults with traumatic brain injury (TBI). However, previous DTI studies of pediatric TBI were case reports without detailed outcome measures. Using mean FA derived from DTI fiber tractography, we compared DTI findings of the corpus callosum for 16 children who were at least 1 year (mean 3.1 years) post-severe TBI and individually matched, uninjured children. Interexaminer and intraexaminer reliability in measuring FA was satisfactory. FA was significantly lower in the patients for the genu, body, and splenium of the corpus callosum. Higher FA was related to increased cognitive processing speed and faster interference resolution on an inhibition task. In the TBI patients, higher FA was related to better functional outcome as measured by the dichotomized Glasgow Outcome Scale (GOS). FA also increased as a function of the area of specific regions of the corpus callosum such as the genu and splenium, and FA in the splenium was reduced with greater volume of lesions in this region. DTI may be useful in identifying biomarkers related to DAI and outcome of TBI in children.

Mechanisms of working memory dysfunction after mild and moderate TBI: evidence from functional MRI and neurogenetics

Cognitive complaints are a frequent source of distress and disability after mild and moderate traumatic brain injury (TBI). While there are deficits in several cognitive domains, many aspects of these complaints and deficits suggest that problems in working memory (WM) play an important role. Functional imaging studies in healthy individuals have outlined the neural substrate of WM and have shown that regions important in WM circuitry overlap with regions commonly vulnerable to damage in TBI. Use of functional MRI (fMRI) in individuals with mild and moderate TBI suggests that they can have problems in the activation and allocation of WM, and several lines of evidence suggest that subtle alterations in central catecholaminergic sensitivity may underlie these problems. We review the evidence from fMRI and neurogenetic studies that support the role of catecholaminergic dysregulation in the etiology of WM complaints and deficits after mild and moderate TBI.

Costs of a predictable switch between simple cognitive tasks following severe closed-head injury

The authors used a predictable, externally cued task-switching paradigm to investigate executive control in a severe closed-head injury (CHI) population. Eighteen individuals with severe CHI and 18 controls switched between classifying whether a digit was odd or even and whether a letter was a consonant or vowel on every 4th trial. The target stimuli appeared in a circle divided into 8 equivalent parts. Presentation of the stimuli rotated clockwise. Participants performed the switching task at both a short (200 ms) and a long (1,000 ms) preparatory interval. Although the participants with CHI exhibited slower response times and greater switch costs, similar to controls, additional preparatory time reduced the switch costs, and the switch costs were limited to the 1st trial in the run. These findings indicate that participants with severe CHI were able to take advantage of time to prepare for the task switch, and the executive control processes involved in the switch costs were completed before the 1st trial of the run ended.

The influence of mild traumatic brain injury on the temporal distribution of attention

The purpose of this study was to examine whether the temporal dynamics of attention was deficient in participants who have recently experienced mild traumatic brain injury (mTBI). For this purpose the rapid serial visual presentation (RSVP) task was used and the performance of participants with mTBI was compared to that of controls matched for age, gender, education, and activity type. In the RSVP task a stream of rapidly presented letters is displayed with target and probe letters separated by varying durations. The participant is required to identify the target letter and determine whether the probe letter was present or not. Previous research has shown that healthy participants display an attentional blink: they fail to detect the probe letter when it appears within approximately 500 ms of the target letter. We found that participants with mTBI had a normal attentional blink-it was neither greater in magnitude nor longer in duration than that displayed by the control participants. However, the participants with mTBI did show evidence of attentional competition-making more errors in identifying the target letter when the probe letter was presented-that was not present in the control participants. Taken together, these results suggest that the temporal constraints of attention are subtly but systematically affected by mTBI.

Cognitive structure of executive deficits in patients with frontal lesions performing activities of daily living

OBJECTIVE

Executive function in activities of daily living (ADL) were investigated in 10 patients with excised frontal lobe tumours.

METHOD

The patients with frontal lesions were compared to 10 normal controls with a neuropsychological test battery, a script generation task and a realistic implementation of complex multi-task ADL (planning and preparing a meal).

RESULTS

The patients manifested numerous basic executive deficits on the paper-pencil tests, were unimpaired on the script generation task despite an aberrant semantic structure and manifested marked anomalies in the meal preparation task.

CONCLUSION

Frontal lobe deficits in lengthy complex multi-task ADL can be explained by impairment of several executive functions, generalized slowness of performance and paucity of behaviour.

Vigilance and fatigue following traumatic brain injury

Research findings have suggested that individuals with traumatic brain injury (TBI) show greater psychophysiological and subjective costs associated with performing vigilance tasks, but have not examined relationships with fatigue. The present study aimed to investigate vigilance and its relationship with subjective and objective fatigue measures. Forty-six TBI participants and 46 controls completed a 45-minute vigilance task. They also completed a subjective fatigue scale (the VAS-F) and a selective attention task before and after the vigilance task, and had their blood pressure (BP) monitored. TBI participants performed at a lower level on the vigilance task, but performed at a similar level across the duration of the task. Higher subjective fatigue ratings on the VAS-F were associated with more misses on the vigilance task for TBI participants. TBI participants showed greater increases in diastolic BP, and these were associated with greater increases in subjective fatigue ratings on the VAS-F. A subgroup of TBI participants showed a decline in performance on the vigilance task and also showed disproportionate increases in subjective fatigue. Findings provide support for the coping hypothesis, suggesting that TBI individuals expend greater psychophysiological costs in order to maintain stable performance over time, and that these costs are also associated with subjective increases in fatigue.

Selective attention deficits and subjective fatigue following traumatic brain injury

The present study aimed to investigate the relationship between subjective fatigue and selective attention deficits following traumatic brain injury (TBI). Forty-six participants with mild-severe TBI and 46 healthy controls completed fatigue scales (Visual Analogue Scale--Fatigue, Fatigue Severity Scale [FSS] and Causes of Fatigue Questionnaire [COF]), and attentional measures including subtests from the Test of Everyday Attention, and the Complex Selective Attention Task (C-SAT). TBI participants reported greater fatigue on the FSS and COF, performed more slowly on attentional measures, and made more errors on the C-SAT. After controlling for anxiety and depression, fatigue was significantly correlated with performance only on the C-SAT. Findings suggest a relationship between subjective fatigue and impairment on tasks requiring higher order attentional processes.

On the neural basis of focused and divided attention

Concepts of higher attention functions distinguish focused and divided attention. The present study investigated whether these mental abilities are mediated by common or distinct neural substrates. In a first experiment, 19 healthy subjects were examined with functional brain imaging (fMRI) while they attended to either one or both of two simultaneously presented visual information streams and responded to repetitive stimuli. This experiment resembled a typical examination of these mental functions with the single task demanding focused and the dual task conditions requiring divided attention. Both conditions activated a widespread, mainly right-sided network including dorso- and ventrolateral prefrontal structures, superior and inferior parietal cortex, and anterior cingulate gyrus. Under higher cognitive demands of divided attention, activity in these structures was enhanced and left-sided homologues were recruited. In a second experiment investigating another 17 subjects with almost the same paradigm, it was accounted for that in most dual task investigations of focused and divided attention the single tasks are easier to process than their combined presentation. Therefore, the task difficulty of focused attention tasks was increased. Almost the same activity pattern observed during division of attention was now found during focusing attention. Comparing both attentional states matched for task difficulty, differences were found in visual but not in prefrontal or parietal cortex areas. Our results suggest that focused and divided attention depend on largely overlapping neuronal substrates. Differences in activation patterns, especially in prefrontal and parietal areas, may result from unequal demands on executive control due to disparate processing requirements in typical tasks of focused and divided attention: Easier conditions begin with mainly right-sided activity within the attention network. As conditions become more difficult, left-lateralized homologue areas activate.

A neuropsychological assessment of dual-task costs in closed-head injury patients using Cohen’s effect size estimation method

A test of whether patients suffering from a severe closed-head injury (CHI) were affected by disproportionate dual-task costs compared to those of healthy control participants was carried out through a direct comparison of CHI effects on dual-task (psychological refractory period, or PRP) performance and on single-task performance. In the dual-task condition of the present experiment, independent choice-responses were required to two sequential stimuli presented at a variable stimulus onset asynchrony (SOA). A significant delay of the reaction time (RT) to the second stimulus was reported by both CHI patients and controls at short (SOA) compared to long SOA, i.e., a PRP effect. The PRP effect was more pronounced for CHI patients than controls. In the single-task condition, a single choice-response was required to a stimulus presented in isolation. The RT produced by CHI patients in the single-task paradigm was longer than the RT produced by controls. CHI effects on dual-task performance and on single-task performance were compared following (1) their transformation into Cohen's ds, and (2) the application of a correction algorithm taking into account the different reliability of single-task and dual-task measures. The analysis of Cohen's ds revealed that CHI effects on performance were, if anything, smaller in the dual-task condition than in the single-task condition. The results imply that CHI patient's slower responding in single- and dual-task performance reflects a single common cause--slowing of the central processing.

Susceptibility weighted imaging: neuropsychologic outcome and pediatric head injury

Traumatic brain injury is among the most frequent pediatric neurologic disorders in the United States, affecting multiple aspects of neuropsychologic functioning. This study assessed the efficacy of susceptibility weighted imaging as a predictor of long-term neuropsychologic functioning after pediatric brain injury compared with magnetic resonance spectroscopic imaging. Susceptibility weighted imaging is a relatively new method that is considered superior to traditional magnetic resonance imaging sequences for detecting hemorrhagic diffuse axonal injury. In this study, imaging and spectroscopy were acquired 6 +/- 4 days after injury. Measures of neuropsychologic functioning were administered to 18 children and adolescents 1-4 years post injury. Negative correlations between lesion number and volume with neuropsychologic functioning were demonstrated. Lesion volume explained over 32% of the variance in cognitive performance, explaining at least an additional 20% beyond injury severity and age at injury alone and 19% beyond magnetic resonance spectroscopic metabolite variables. Exploratory analyses resulted in notable trends, with lesions in deeper brain regions more strongly associated with poorer neuropsychologic performance. Improved detection of the extent of diffuse axonal injury following a brain injury will allow for a better understanding of its association with long-term outcome, which in turn can improve prognostic efficacy for effective treatment planning.

Cognitive Control in Closed Head Injury: Context Maintenance Dysfunction or Prepotent Response Inhibition Deficit?

The authors contrasted 2 potential explanations for the cognitive control deficits observed in closed head injury (CHI): a prepotent response inhibition deficit or a deficit in context maintenance, defined as the guidance of appropriate responding by task-relevant information. Healthy and CHI participants performed the traditional card Stroop task and a single-trial Stroop task sensitive to context maintenance deficits. As predicted by a context maintenance deficit, moderate to severe CHI participants showed higher error rates in the single-trial Stroop task only, and only when task instructions had to be maintained over a long delay. Moreover, context maintenance impairment and generalized slowing were both related to reports of daily functioning in CHI participants. Thus, context maintenance could be a useful framework for characterizing cognitive control deficits in CHI.

Syndromes frontaux et dysexécutifs

Investigation of executive functions is an approach which began with the early description of behavioral disorders induced by frontal damage. The development of neuropsychology has led to the description of a large variety of cognitive disorders. This type of approach has generated a large number of tests which are still used in clinical practice. More recently, theoretical approaches have proposed an organization of executive processes and have documented the diversity of executive functions and related anatomy. These studies have deeply influenced the clinical approach, the assessment and the diagnosis of executive disorders. For clinical practice, these data favor specific assessment of certain key behavioral and cognitive deficits investigated with a battery of tests.

Parametric manipulation of working memory load in traumatic brain injury: behavioral and neural correlates

Traumatic brain injury (TBI) is often associated with enduring impairments in high-level cognitive functioning, including working memory (WM). We examined WM function in predominantly chronic patients with mild, moderate and severe TBI and healthy comparison subjects behaviorally and, in a small subset of moderate-to-severe TBI patients, with event-related functional magnetic resonance imaging (fMRI), using a visual n-back task that parametrically varied WM load. TBI patients showed severity-dependent and load-related WM deficits in performance accuracy, but not reaction time. Performance of mild TBI patients did not differ from controls; patients with moderate and severe TBI were impaired, relative to controls and mild TBI patients, but only at higher WM-load levels. fMRI results show that TBI patients exhibit altered patterns of activation in a number of WM-related brain regions, including the dorsolateral prefrontal cortex and Broca's area. Examination of the pattern of behavioral responding and the temporal course of activations suggests that WM deficits in moderate-to-severe TBI are due to associative or strategic aspects of WM, and not impairments in active maintenance of stimulus representations. Overall, results demonstrate that individuals with moderate-to-severe TBI exhibit WM deficits that are associated with dysfunction within a distributed network of brain regions that support verbally mediated WM.

Closed head injury and perceptual processing in dual-task situations

Using a classical psychological refractory period (PRP) paradigm we investigated whether increased interference between dual-task input processes is one possible source of dual-task deficits in patients with closed-head injury (CHI). Patients and age-matched controls were asked to give speeded motor reactions to an auditory and a visual stimulus. The perceptual difficulty of the visual stimulus was manipulated by varying its intensity. The results of Experiment 1 showed that CHI patients suffer from increased interference between dual-task input processes, which is related to the salience of the visual stimulus. A second experiment indicated that this input interference may be specific to brain damage following CHI. It is not evident in other groups of neurological patients like Parkinson's disease patients. We conclude that the non-interfering processing of input stages in dual-tasks requires cognitive control. A decline in the control of input processes should be considered as one source of dual-task deficits in CHI patients.

A meta-analytic review of verbal fluency performance following focal cortical lesions

A meta-analysis of 31 studies with 1,791 participants was conducted to investigate the sensitivity of tests of verbal fluency to the presence of focal cortical lesions. Relative to healthy controls, participants with focal frontal injuries had large and comparable deficits on phonemic (r = .52) and semantic (r = .54) fluency. For frontal but not nonfrontal patients, phonemic fluency deficits qualified as differential deficits when compared with IQ and psychomotor speed; phonemic fluency was also more strongly and more specifically related to the presence of frontal lesions than the Wisconsin Card Sorting Test scores. In contrast, temporal damage was associated with a lesser deficit on phonemic fluency (r = .44) but a larger deficit on semantic fluency (r = .61).

Working memory deficits after traumatic brain injury: catecholaminergic mechanisms and prospects for treatment -- a review

PRIMARY OBJECTIVE

To review the neural circuitry and neurochemistry of working memory and outline the evidence for working memory deficits after traumatic brain injury, and the evidence for the use of catecholaminergic agents in the amelioration of these deficits. Current knowledge gaps and research needs are identified.

MAIN OUTCOMES AND RESULTS

Impairments in working memory are a core component of the cognitive deficits associated with traumatic brain injury. Recent progress in understanding the neural circuitry and neurochemistry of working memory suggests that catecholamines play a central role in the activation and regulation of working memory and thus lays a framework in which to consider the use of catecholaminergic agents (dopaminergic and alpha-2 adrenergic agonists) in the treatment of specific cognitive deficits after traumatic brain injury.

CONCLUSIONS

The combined methods of cognitive neuroscience, functional brain imaging and neuropharmacology are proposed as an excellent method for studying working memory deficits. A strong rationale exists for the targeted use of catecholaminergic agonists in the treatment of working memory deficits after traumatic brain injury.

Performance of university students on random number generation at different rates to evaluate executive functions

OBJECTIVE: To evaluate the performance of adult young subjects in a Random Number Generation (RNG) task by controlling the response speed (RS). METHOD: Sixty-nine university students of both sexes took part in the experiment (25.05 ± 6.71 year-old). Participants were alloted into 3 groups which differed in RS rates to generate numbers: 1, 2 and 4 seconds to generate each number. A digital metronomer was used to control RS. Participants were asked to generate 100 numbers. The responses were mensured through Evans's RNG Index. RESULTS: There were statistically significant differences among the groups [F (3, 68) = 7.120; p < .05]. Differences were localized between 1 and 2 seconds (p = 0.004) and between 1 and 4 seconds (p = 0.006). No differences were observed between 2 and 4 seconds (p = 0.985). CONCLUSION: The present results suggest that the response speed in production of random numbers influences the performance of the Random Numbers Generation task.