Age-related changes in cognitive conflict processing: An event-related potential study

Electrophysiological indexes of ingroup bias in a group Stroop task: Evidence from an event-related potential study

Although cognitive system assigns higher attentional resources to ingroup information than outgroup information, but it is unclear whether the ingroup bias can be measured by the processes that are related to allocation of attentional resources to ingroup information. Thus, a group Stroop task was developed to study the issues combining with event-related potential (ERP) technique in this study. Specifically, 34 subjects (17 female, mean age = 20.76 ± 1.26) were firstly divided into blue or red group (17 subjects for each group); then they were asked to categorize four words of Stroop task into "our team" or "other team" based on the ink color (blue/red) of the words whose meaning were also red/blue. The behavioral results showed that outgroup ink color processing was interfered by ingroup word meaning, but the ingroup ink color processing was less/not interfered by outgroup word meaning. The ERP results showed that the amplitude of frontal N100 was enhanced when more attentional resources were automatically captured by ingroup information in early stage than outgroup information; P2/N2 amplitude was reduced or enhanced when outgroup information processing was interfered by ingroup information; enhanced P3b amplitude reflected that attention could be more easily allocated to ingroup information than outgroup information based on target. This study implied a novel direction to study the neural basis of ingroup bias by investigating the roles of ingroup bias in assigning attentional resources to group information.

Time Course of Reactive Brain Activities during a Stroop Color-Word Task: Evidence of Specific Facilitation and Interference Effects

The Stroop test represents a widely used task in basic and clinical research for approaching the cognitive system functioning in humans. However, a clear overview of the neurophysiological signatures associated with the different sub-domains of this task remains controversial. In the present study, we leveraged the EEG technique to explore the modulation of specific post-stimulus ERPs components during the Stroop test. Critically, to better disentangle the contribution of facilitation (i.e., faster color identification times for color-congruent Stroop words) and interference (i.e., longer color identification times for color-incongruent Stroop words) processes prompted by the Stroop test, we delivered congruent and incongruent trials in two separate experimental blocks, each including the respective neutral condition. Thanks to this methodological manipulation, we were able to clearly dissociate the two sub-processes. Electrophysiological results suggest specific markers of brain activity for the facilitation and the interference effects. Indeed, distinctive Stroop-related ERPs (i.e., the P3, the N450, and the LPC) were differently modulated in the two sub-processes. Collectively, we provide evidence of selected brain activities involved in the reactive stage of processing associated with the Stroop effect.

Cognitive control, bedtime patterns, and testing time in female adolescent students: behavioral and neuro-electrophysiological correlates

Introduction

Shorter and/or disrupted sleep during adolescence is associated with cognitive and mental health risks, particularly in females. We explored the relationship between bedtime behavior patterns co-varying with Social Jet Lag (SJL) and School Start Times (SST) and neurocognitive performance in adolescent female students.

Methods

To investigate whether time of day (morning vs. afternoon), early SSTs and days of the school week can be correlated with neurocognitive correlates of sleep insufficiency, we recruited 24 female students aged 16-18 to report sleep logs, and undergo event-related electroencephalographic recordings on Monday, Wednesday, mornings, and afternoons. Using a Stroop task paradigm, we analyzed correlations between reaction times (RTs), accuracy, time of day, day of week, electroencephalographic data, and sleep log data to understand what relationships may exist.

Results

Participants reported a 2-h sleep phase delay and SJL. Stroop interference influenced accuracy on Monday and Wednesday similarly, with better performance in the afternoon. For RTs, the afternoon advantage was much larger on Monday than Wednesday. Midline Event-Related Potentials (ERPs) yielded higher amplitudes and shorter latencies on Wednesday morning and Monday afternoon, in time windows related to attention or response execution. A notable exception were delayed ERP latencies on Wednesday afternoon. The latter could be explained by the fact that delta EEG waves tended to be the most prominent, suggesting heightened error monitoring due to accumulating mental fatigue.

Discussion

These findings provide insights into the interaction between SJL and SST and suggest evidence-based criteria for planning when female adolescents should engage in cognitive-heavy school activities such as tests or exams.

The temporal dynamics of the Stroop effect from childhood to young and older adulthood

The processes involved in the Stroop task/effect are thought to involve conflict detection and resolution stages. Little is known about the evolution of these two components over the lifespan. It is well admitted that children and older adults tend to show longer response latencies than young adults. The present study aims at clarifying the rational of such changes from childhood to adulthood and in aging by comparing the impacted cognitive processes across age groups. More precisely, the aim was to clarify if all processes take more time to be executed, hence implying that longer latencies rely mainly on processing speed or if an additional process lengthens the resolution of the conflict in children and/or older adults. To this aim we recorded brain electrical activity using EEG in school-age children, young and older adults while they performed a classic verbal Stroop task. The signal was decomposed in microstate brain networks, and age groups and conditions were compared. Behavioral results evolved following an inverted U-shaped curve. In children, different brain states from the ones observed in adults were highlighted, both in the conflict detection and resolution time-windows. Longer latencies in the incongruent condition were mainly attributed to an overly increased duration of the microstates involved in the conflict resolution time window. In aging, the same microstate maps were reported for both young and older adult groups. The differences in performances between groups could be explained by a disproportionally long conflict detection phase, even compressing the latest stage of response articulation. These results tend to favor a specific immaturity of the brain networks involved coupled with a slowing of the processes in children, while cognitive decline could be mostly explained by a general slowing.

Electrophysiological Evidence of Anticipatory Cognitive Control in the Stroop Task

The Stroop task has been largely used to explore the ability to inhibit the automatic process of reading when reporting the ink color of incongruent color-words. Given the extensive literature regarding the processes involved in task performance, here we aimed at exploring the anticipatory brain activities during the Stroop task using the event-related potential (ERP) method. To accomplish this, eighteen participants performed two different blocks where neutral words were intermixed with congruent and incongruent words, respectively. Results revealed consistent pre-stimulus activity over the frontal, premotor and parietal brain areas. The premotor and the parietal activities were also modulated by the Stroop effect, being more enhanced in the incongruent than in the congruent blocks. Present findings add on the current literature pointing at an unexplored locus of anticipatory cognitive control during task preparation, thus offering a new way to investigate top-down preparatory processes of performance control in the Stroop task.

Intermodal Priming of Cognitive Conflict? A Failed Replication of Mager et al. (2009)

Introduction: The present study was conducted to verify a promising experimental setup which demonstrated an inversed Stroop-effect (much faster responses for incongruent relative to congruent Stroop trials) following a mismatching tone. In the matching condition, which was an almost exact replication of the original study, participants were required to indicate whether word color and word meaning were matching, whereas in the response conflict condition, instruction was the same as in a classical Stroop task and required the participants to respond to the word color. As in the original study, each trial was preceded by a sine tone which was deviant in pitch in 20% of the trials. Results: The main result was that the Stroop effect was not inversed after deviant tones, neither under the matching task instruction nor under the response conflict task instruction. The Stroop effect was unaffected by the previous "conceptual mismatch." Conclusion: The current study failed to replicate the astonishing concept of "conflict priming" reported in previous work and does not open the doors for a new window on sequences of conflicts. Nevertheless, the failed replication is valuable for future research, since it demonstrated that "Conflict Priming" as a facilitation of processing of conflict trials following deviant tones, is not an confirmed finding.

An ERP investigation of the working memory stroop effect

This study aimed to explore the neural activity associated with the Working Memory (WM) Stroop effect. Stroop facilitation and interference effects in WM were also investigated by adding a neutral condition to the WM Stroop paradigm. In each trial, participants were first asked to remember a word in WM, then respond to the color of the subsequent rectangle. The word meaning and rectangular color were congruent, incongruent, or irrelevant (neutral). Finally, a probe word appeared and participants judged whether it was the same as the first presented word. For the color decision task, behavioral results showed that 1) RTs were longer for the incongruent than congruent condition, indicating a WM Stroop effect; 2) RTs were shorter for the congruent than neutral condition, indicating a WM Stroop facilitation effect; and 3) RTs were shorter for the incongruent than neutral condition, indicating no Stroop interference effect in WM. ERPs locked to the rectangle revealed that 1) greater N2 and P3 activity was evoked for the incongruent than congruent condition, indicating more intensive conflict detection and conflict resolution processes for the incongruent condition; and 2) enhanced N2 but decreased P3 components were evoked for the neutral than the congruent and incongruent conditions, indicating a more intensive conflict monitoring process but decreased conflict resolution process for the neutral condition. These results demonstrate that when WM content is congruent with the attention task, it can facilitate attention, but WM content may not interfere with attention when they are incongruent.

Attentional Bias Deficits in Adolescent Suicide Attempters During an Emotional Stroop Task: An ERP Study

There is increasing evidence that, in adolescence, attentional bias plays a critical role in the vulnerability for suicidal behaviour. No studies to date have investigated the neurophysiological correlates of attentional bias in adolescent suicidality. The present study uses event-related potentials (ERPs) to investigate such processing in inpatient adolescents admitted for an acute suicide crisis using an Emotional Stroop Task (EST). In this task, participants are asked to name the colour of words varying in emotional valence (positive, negative, neutral, suicide-related). Suicidal individuals are hypothesised to be more preoccupied by the context of the suicide-related stimuli, which may interfere with their ability to perform the colour naming task. Seventeen adolescents with acute suicidal behaviour and 17 age- and gender-matched healthy controls performed an EST while ERPs were recorded. Suicide attempters showed increased reaction times to suicide-related words compared to other emotion categories, while the controls did not. The amplitude of the early posterior negativity (EPN) was not significantly different across groups or emotional valence. A double peak P3 (early-P3 and late-P3) was observed in both groups. Both the early- and late-P3 were significantly reduced in amplitude in the suicide attempter group compared to the control group, regardless of emotional valence. The late-P3 latency was also significantly delayed in the suicide attempters compared to controls. The behavioural findings support the attentional bias theories of suicide attempters and extend these findings to adolescents. Furthermore, large early- and late-P3 provide evidence that cognitive strategies employed by two groups did markedly differ.

Acute Exercise Facilitates the N450 Inhibition Marker and P3 Attention Marker during Stroop Test in Young and Older Adults

While considerable evidence supporting the positive influence of acute exercise on cognitive inhibition, little is known regarding the underlying cognitive processes. There is also little neuroelectric evidence regarding the effects on older adults of acute exercise-elicited cognitive benefits. Thus, our objective was to explore the possible neural markers underlying improved cognitive inhibition, with particular attention to the N450 and P3 components, following acute exercise. Another aim was to investigate whether cognitive gains seen in young adults are replicated in older adults. Twenty-four young males and 20 older males underwent either a single bout of aerobic exercise or video-watching in counterbalanced order. Afterwards, cognitive inhibition was assessed by the Stroop test. Results revealed that acute exercise resulted in shorter response time regardless of age or congruency. Regarding the neuroeletric data, acute exercise resulted in larger P3 amplitude and smaller N450 amplitude regardless of congruency or age. Further, following exercise, changes in response time interference were correlated with changes in incongruent N450 amplitude. Collectively, acute exercise-facilitated conflict monitoring and attention control, as signified by the N450 and P3 components, may be the underlying processes leading to better Stroop performance, with conflict monitoring having a stronger association with task performance. Further, cognitive gains resulting from acute exercise were found to the same extent in both young and older adults.

The impact of natural aging on computational and neural indices of perceptual decision making: A review

It is well established that natural aging negatively impacts on a wide variety of cognitive functions and research has sought to identify core neural mechanisms that may account for these disparate changes. A central feature of any cognitive task is the requirement to translate sensory information into an appropriate action - a process commonly known as perceptual decision making. While computational, psychophysical, and neurophysiological research has made substantial progress in establishing the key computations and neural mechanisms underpinning decision making, it is only relatively recently that this knowledge has begun to be applied to research on aging. The purpose of this review is to provide an overview of this work which is beginning to offer new insights into the core psychological processes that mediate age-related cognitive decline in adults aged 65 years and over. Mathematical modelling studies have consistently reported that older adults display longer non-decisional processing times and implement more conservative decision policies than their younger counterparts. However, there are limits on what we can learn from behavioural modeling alone and neurophysiological analyses can play an essential role in empirically validating model predictions and in pinpointing the precise neural mechanisms that are impacted by aging. Although few studies to date have explicitly examined correspondences between computational models and neural data with respect to cognitive aging, neurophysiological studies have already highlighted age-related changes at multiple levels of the sensorimotor hierarchy that are likely to be consequential for decision making behaviour. Here, we provide an overview of this literature and suggest some future directions for the field.

Two Different Populations within the Healthy Elderly: Lack of Conflict Detection in Those at Risk of Cognitive Decline

During healthy aging, inhibitory processing is affected at the sensorial, perceptual, and cognitive levels. The assessment of event-related potentials (ERPs) during the Stroop task has been used to study age-related decline in the efficiency of inhibitory processes. Studies using ERPs have found that the P300 amplitude increases and the N500 amplitude is attenuated in healthy elderly adults compared to those in young adults. On the other hand, it has been reported that theta excess in resting EEG with eyes closed is a good predictor of cognitive decline during aging 7 years later, while a normal EEG increases the probability of not developing cognitive decline. The behavioral and ERP responses during a Counting-Stroop task were compared between 22 healthy elderly subjects with normal EEG (Normal-EEG group) and 22 healthy elderly subjects with an excess of EEG theta activity (Theta-EEG group). Behaviorally, the Normal-EEG group showed a higher behavioral interference effect than the Theta-EEG group. ERP patterns were different between the groups, and two facts are highlighted: (a) the P300 amplitude was higher in the Theta-EEG group, with both groups showing a P300 effect in almost all electrodes, and (b) the Theta-EEG group did not show an N500 effect. These results suggest that the diminishment in inhibitory control observed in the Theta-EEG group may be compensated by different processes in earlier stages, which would allow them to perform the task with similar efficiency to that of participants with a normal EEG. This study is the first to show that healthy elderly subjects with an excess of theta EEG activity not only are at risk of developing cognitive decline but already have a cognitive impairment.

Brain Changes Following Executive Control Training in Older Adults

BACKGROUND

While older adults are able to attend to goal-relevant information, the capacity to ignore irrelevant or distracting information declines with advancing age. This decline in selective attention has been associated with poor modulation of brain activity in sensory cortices by anterior brain regions implicated in cognitive control.

OBJECTIVE

Here we investigated whether participation in an executive control training program would result in improved selective attention and associated functional brain changes in a sample of healthy older adults (N = 24, age 60-85 years).

METHODS

Participants were enrolled in a goal-oriented attentional self-regulation (GOALS) program (n = 11) or a brain health education workshop as an active control condition (n = 13). All participants performed a working memory task requiring attention to or suppression of visual stimuli based on goal-relevance during functional magnetic resonance imaging.

RESULTS

We observed a pattern of enhanced activity in right frontal, parietal and temporal brain regions from pre- to posttraining in the GOALS intervention group, which predicted the selectivity of subsequent memory for goal-relevant stimuli.

CONCLUSIONS

Executive control training in older adults alters functional activity in brain regions associated with attentional control, and selectively predicts behavioral outcome.

Prefrontal cortex-mediated executive function as assessed by Stroop task performance associates with weight loss among overweight and obese adolescents and young adults

People with cognitive deficits or executive dysfunction are often overweight or obese. Several human neuroimaging studies have found that executive function (EF) predicts food intake and weight gain; however, fewer studies have investigated the relationship between EF and weight loss. The Stroop task is a classic measure of EF that is used in many neuroimaging studies. In the present work, functional near infrared spectroscopy (fNIRS) data were collected during performance of the Stroop task from a sample of overweight or obese adolescents and young adults (n=31) who participated in a summer fitness and weight loss camp. We assessed the Stroop effect by interference in the reaction time (RT) to visual challenges, and by alterations in levels of oxygenated hemoglobin, as detected by fNIRS. In line with previous studies, we found that the Stroop effect was successfully induced by different visual task conditions among obese/overweight individuals. Moreover, our results reveal that better Stroop task performance is correlated with greater weight loss over a4-weekfitness intervention. Indeed, behavioral data demonstrated that reduced RT interference predicted a greater percentage of weight loss. Moreover, overweight/obese individuals with a greater hemodynamic response in the left ventrolateral and bilateral dorsolateral prefrontal cortex due to the Stroop effect lost more weight during the short-term fitness intervention than participants with lower levels of activation of these neural regions. Overall, our results support a role for prefrontal cortex-mediated EF in influencing food intake and weight loss outcomes in a population of a previously unstudied age.

Conflict-Specific Aging Effects Mainly Manifest in Early Information Processing Stages-An ERP Study with Different Conflict Types

Aging is usually accompanied by alterations of cognitive control functions such as conflict processing. Recent research suggests that aging effects on cognitive control seem to vary with degree and source of conflict, and conflict specific aging effects on performance measures as well as neural activation patterns have been shown. However, there is sparse information whether and how aging affects different stages of conflict processing as indicated by event related potentials (ERPs) such as the P2, N2 and P3 components. In the present study, 19 young and 23 elderly adults performed a combined Flanker conflict and stimulus-response-conflict (SRC) task. Analysis of the reaction times (RTs) revealed an increased SRC related conflict effect in elderly. ERP analysis furthermore demonstrated an age-related increase of the P2 amplitude in response to the SRC task. In addition, elderly adults exhibited an increased P3 amplitude modulation induced by incongruent SRC and Flanker conflict trials.

Pre-stimulus alpha and post-stimulus N2 foreshadow imminent errors in a single task

Performance errors have been attributed to distinct neural mechanisms in different tasks. Two temporally and physiologically dissociable neural patterns prior to errors, i.e., pre-stimulus alpha (8-13 Hz) power indicative of sustained attention and post-stimulus N2 amplitude indicative of cognitive control, have been widely (but independently) reported in many studies. However, it is still largely unknown whether these two neural mechanisms for error commission exist in a single task at the same time and, if so, whether they can be probed simultaneously and how they lead to response accuracy (collectively or separately). To this end, we measured high-density electroencephalography (EEG) signals in a color-word matching Stroop task. We quantified both patterns on EEG data from individual stimulus condition (congruent or incongruent), as well as on pooled data from both conditions. Enhanced pre-stimulus alpha power for errors was identified over the parieto-occipital area in the congruent condition and the pooled data. Reduced post-stimulus N2 amplitude was only revealed in the incongruent condition. More importantly, for the first time, a balanced interaction between these two EEG patterns was revealed in correct trials, but not in error trials. These findings suggest that errors in one task could occur due to distinct neural mechanisms, e.g., poor sustained attention, poor cognitive control, or missed balance between these two. The present results further suggest that the detection of neural patterns related to different neural mechanisms could be complicated by other modulation factors, such as stimulus condition. Therefore, more than one neural marker should be simultaneously monitored to effectively predict imminent errors.

Dual-task and electrophysiological markers of executive cognitive processing in older adult gait and fall-risk

The role of cognition is becoming increasingly central to our understanding of the complexity of walking gait. In particular, higher-level executive functions are suggested to play a key role in gait and fall-risk, but the specific underlying neurocognitive processes remain unclear. Here, we report two experiments which investigated the cognitive and neural processes underlying older adult gait and falls. Experiment 1 employed a dual-task (DT) paradigm in young and older adults, to assess the relative effects of higher-level executive function tasks (n-Back, Serial Subtraction and visuo-spatial Clock task) in comparison to non-executive distracter tasks (motor response task and alphabet recitation) on gait. All DTs elicited changes in gait for both young and older adults, relative to baseline walking. Significantly greater DT costs were observed for the executive tasks in the older adult group. Experiment 2 compared normal walking gait, seated cognitive performances and concurrent event-related brain potentials (ERPs) in healthy young and older adults, to older adult fallers. No significant differences in cognitive performances were found between fallers and non-fallers. However, an initial late-positivity, considered a potential early P3a, was evident on the Stroop task for older non-fallers, which was notably absent in older fallers. We argue that executive control functions play a prominent role in walking and gait, but the use of neurocognitive processes as a predictor of fall-risk needs further investigation.

Age-related differences in early novelty processing: using PCA to parse the overlapping anterior P2 and N2 components

Previous work demonstrated age-associated increases in the anterior P2 and age-related decreases in the anterior N2 in response to novel stimuli. Principal component analysis (PCA) was used to determine if the inverse relationship between these components was due to their temporal and spatial overlap. PCA revealed an early anterior P2, sensitive to task relevance, and a late anterior P2, responsive to novelty, both exhibiting age-related amplitude increases. A PCA factor representing the anterior N2, sensitive to novelty, exhibited age-related amplitude decreases. The late P2 and N2 to novels inversely correlated. Larger late P2 amplitude to novels was associated with better behavioral performance. Age-related differences in the anterior P2 and N2 to novel stimuli likely represent age-associated changes in independent cognitive operations. Enhanced anterior P2 activity (indexing augmentation in motivational salience) may be a compensatory mechanism for diminished anterior N2 activity (indexing reduced ability of older adults to process ambiguous representations).

Detection of EEG spatial-spectral-temporal signatures of errors: a comparative study of ICA-based and channel-based methods

The present study aimed to investigate the sensitivity of independent component analysis (ICA)- and channel-based methods in detecting electroencephalography (EEG) spatial-spectral-temporal signatures of performance errors. 128-channel EEG signals recorded from 18 subjects, who performed a color-word matching Stroop task, were analyzed. The spatial-spectral-temporal patterns in event-related potentials (ERPs) and oscillatory activities (i.e., power and phase) were measured at four selected channels, i.e., FCz, Pz, O1 and O2, from original EEG data after preprocessing, EEG data after additional current source density (CSD) transform, and back-projected EEG data from individual ICs after additional ICA analysis. Pair-wise correlation coefficient (CC) and mutual information (MI), calculated from three EEG data at four selected channels, were compared to examine mutual correlations in EEG signals obtained through three different means. Thereafter, EEG signatures of errors from these three means were statistically compared at multiple time windows in the contrast of error and correct responses. Significantly decreased CC and MI values were observed in CSD- and ICA-processed EEGs as compared with original EEG, with the smallest CC and MI in ICA EEG. Similar error patterns in ERPs and peri-response oscillatory activities were detected in all three EEGs, whereas the pre-stimulus and post-stimulus error-related oscillatory patterns identified in ICA EEG were either not or only partially detected in both original EEG and CSD EEGs in general. Both CSD and ICA processes can largely reduce signal correlations due to the volume conduction effect in original EEG, and EEG signatures of errors are better detected by ICA-based method than channel-based method (i.e., original and CSD EEGs). ICA provides the best sensitivity to detect EEG signatures linked to specific neural processes via disentangling superimposed channel-level EEG signals into distinct neurocognitive process-related component signals.

Age Differences in the Processing of Context Information

The dual mechanisms of control theory (DMC; Braver & Barch, 2002 ) assumes that age-related changes in the temporal structure of context processing underlie age differences in numerous cognitive control tasks. Younger adults usually exhibit a proactive control mode, characterized by cue-related context updating, while older adults show a reactive control mode, updating information when interference is detected. This study aimed at determining whether age differences in electrophysiological correlates of context updating in a pro-and reactive manner are independent of individual differences in task performance. To this end, younger and older adults were split into four groups according to their updating efficiency in behavioral data. Nineteen younger and 18 older adults completed a modified AX-Continuous-Performance Task ( Lenartowicz, Escobedo-Quiroz, & Cohen, 2010 ) in which correct responses to probes were either dependent (c-dep) or independent (c-indep) on a preceding contextual cue. Analysis of the behavioral data showed no differences in context updating when performance was matched, that is, between low performing younger and high performing older adults. However, low performing younger adults showed larger cue-locked parietal P3b amplitudes on c-dep than c-indep trials, indicating c-dep trials to require context updating to a larger extent, while high performing older adults exhibited a specific control strategy and continuously updated context information, as reflected in comparable P3b amplitudes on c-dep and c-indep trials. The persistent age effect in the P3b when controlling for performance differences suggests context updating to be fundamental to cognitive aging. High performing in contrast to low performing older adults also showed a larger negative N450 to ambiguous probes on c-dep trials associated with conflict detection. According to the DMC, this finding suggests late conflict detection at the time interference is detected, indicative of a reactive control style particular in high performing elderly.

Flexible connectivity in the aging brain revealed by task modulations

Recent studies have shown that aging has a large impact on connectivity within and between functional networks. An open question is whether elderly still have the flexibility to adapt functional network connectivity (FNC) to the demands of the task at hand. To study this, we collected fMRI data in younger and older participants during resting state, a selective attention (SA) task and an n-back working memory task with varying levels of difficulty. Spatial independent component (IC) analysis was used to identify functional networks over all participants and all conditions. Dual regression was used to obtain participant and task specific time-courses per IC. Subsequently, functional connectivity was computed between all ICs in each of the tasks. Based on these functional connectivity matrices, a scaled version of the eigenvector centrality (SEC) was used to measure the total influence of each IC in the complete graph of ICs. The results demonstrated that elderly remain able to adapt FNC to task demands. However, there was an age-related shift in the impetus for FNC change. Older participants showed the maximal change in SEC patterns between resting state and the SA task. Young participants, showed the largest shift in SEC patterns between the less demanding SA task and the more demanding 2-back task. Our results suggest that increased FNC changes from resting state to low demanding tasks in elderly reflect recruitment of additional resources, compared with young adults. The lack of change between the low and high demanding tasks suggests that elderly reach a resource ceiling.

Age-related effects on event-related brain potentials in a congruence/incongruence judgment color-word Stroop task

We examined the event-related brain potentials elicited by color-word stimuli in a Stroop task in which healthy participants (young and old) had to judge whether the meaning and the color of the stimulus were congruent or incongruent. The Stroop effect occurred in both age groups, with longer reaction times in the older group than in the young group for both types of stimuli, but no difference in the number of errors made by either group. Although the N2 and P3b latencies were longer in the older than in the younger group, there were no differences between groups in the latencies of earlier event-related potential components, and therefore the age-related processing slowing is not generalized. The frontal P150 amplitude was larger, and the parietal P3b amplitude was smaller, in the older than in the younger group. Furthermore, the P3b amplitude was maximal at frontal locations in older participants and at parietal locations in young participants. The age-related increase in perceptual resources and the posterior-to-anterior shift in older adults support adaptive reorganization of the neural networks involved in the processing of this Stroop-type task.

Brain mechanisms underlying the effects of aging on different aspects of selective attention

The ability to suppress irrelevant information declines with age, while the ability to enhance relevant information remains largely intact. We examined mechanisms behind this dissociation in an fMRI study, using a selective attention task in which relevant and irrelevant information appeared simultaneously. Slowing of response times due to distraction by irrelevant targets was larger in older than younger participants. Increased distraction was related to larger increases in activity and connectivity in areas of the dorsal attention network, indicating a more pronounced (re-)orientation of attention. The decreases in accuracy in target compared to nontarget trials were smaller in older compared to younger participants. In older adults we found increased recruitment of areas in the fronto-parietal control network (FPCN) during target detection. Moreover, older adults showed increased connectivity between the FPCN, supporting cognitive control, and somatomotor areas implicated in response selection and execution. This connectivity increase was related to improved target detection, suggesting that older adults engage additional cognitive control, which might enable the observed intact performance in detecting and responding to target stimuli.

Neural markers for immediate performance accuracy in a Stroop color-word matching task: an event-related potentials analysis

The present study examined the neural markers measured in event-related potentials (ERPs) for immediate performance accuracy during a cognitive task with less conflict, i.e., a Stroop color-word matching task, in which participants were required to judge the congruency of two feature dimensions of a stimulus. In an effort to make ERP components more specific to distinct underlying neural substrates, recorded EEG signals were firstly dissolved into multiple independent components (ICs) using independent component analysis (ICA). Thereafter, individual ICs with prominent sensory- or cognitive-related ERP components were selected to separately reconstruct scalp EEG signals at representative channels, from which ERP waveforms were built, respectively. Statistical comparisons on amplitudes of stimulus-locked ERP components, i.e., prefrontal P2 and N2, parietal P3, bilateral occipital P1 and N1, revealed significant reduced P3 amplitude in error trials than in correct trials. In addition, significant evident ERN was also observed in error trials but not in correct trials. Considering the temporal locus of semantic conflict in the present task, we concluded that reduced P3 amplitude in error trials reflect impaired resolving process of semantic conflict, which further lead to a performance error in the Stroop color-word matching task.

Asymmetry in stimulus and response conflict processing across the adult lifespan: ERP and EMG evidence

Several studies have shown that conflict processing improves from childhood to adulthood and declines from adulthood to old age. However the neural mechanisms underlying this lifespan asymmetry were previously unexplored. We combined event-related potentials (ERPs) and electromyography (EMG) to examine lifespan changes in stimulus and response conflict processing using a modified Stroop task. We used a Stroop task that a priori dissociated stimulus and response conflict. Delayed P3b latency and increased amplitude revealed that middle age adults have a deficit in stimulus processing. Additionally a sustained P3a across frontal and central electrodes occurred only in middle age adults indicating the recruitment of frontal activity. Conversely, decreased lateralized readiness potential (LRP) amplitude and increased EMG activity in the incorrect hand in adolescents reveal protracted development of response processing into late adolescence. The N450, a measure of conflict processing, was found to be sensitive to both stimulus and response conflict. Altogether these results provide evidence for asymmetrical differences in stimulus and response conflict processing across adolescence, young adulthood and middle age.

Semantic Conflict Processing in the Color-Word Stroop and the Emotional Stroop

With the aim of establishing the temporal locus of the semantic conflict in color-word Stroop and emotional Stroop phenomena, we analyzed the Event-Related Potentials (ERPs) elicited by nonwords, incongruent and congruent color words, colored words with positive and negative emotional valence, and colored words with neutral valence. The incongruent, positive, negative, and neutral stimuli produced interference in the behavioral response to the color of the stimuli. The P150/N170 amplitude was sensitive to the semantic equivalence of both dimensions of the congruent color words. The P3b amplitude was smaller in response to incongruent color words and to positive, negative, and neutral colored words than in response to the congruent color words and colored nonwords. There were no differences in the ERPs induced in response to colored words with positive, negative, and neutral valence. Therefore, the P3b amplitude was sensitive to interference from the semantic content of the incongruent, positive, negative, and neutral words in the color-response task, independently of the emotional content of the colored words. In addition, the P3b amplitude was smaller in response to colored words with positive, negative, and neutral valence than in response to the incongruent color words. Overall, these data indicate that the temporal locus of the semantic conflict generated by the incongruent color words (in the color-word Stroop task) and by colored words with positive, negative, and neutral valence (in the emotional Stroop task) appears to occur in the range 300–450 ms post-stimulus.

The Met-genotype of the BDNF Val66Met polymorphism is associated with reduced Stroop interference in elderly

Aging is accompanied by impairments of executive functions that rely on the functional integrity of fronto-striatal networks. This integrity is modulated by the release of neurotrophins like the brain-derived-neurotrophic factor (BDNF). Here, we investigate effects of the functional BDNF Val66Met polymorphism on interference processing in 131 healthy elderly subjects using event-related potentials (ERPs). In a Stroop task, participants had to indicate the name or the colour of colour-words while colour was either compatible or incompatible with the name. We show that susceptibility to Stroop-interference is affected by the BDNF Val66Met polymorphism: the Met-allele carriers showed better performance and enhanced N450 in interference trials. Other processes necessary to prepare and allocate cognitive resources to a particular task were not affected by BDNF Val66Met polymorphism, underlining the specificity of the observed effects. The observed performance and ERP difference is possibly due to dopamine related effects of BDNF in fronto-striatal networks, where it putatively mediates a shift in the balance of the direct and indirect pathway involved in inhibitory functions.

Normal aging delays and compromises early multifocal visual attention during object tracking

Declines in selective attention are one of the sources contributing to age-related impairments in a broad range of cognitive functions. Most previous research on mechanisms underlying older adults' selection deficits has studied the deployment of visual attention to static objects and features. Here we investigate neural correlates of age-related differences in spatial attention to multiple objects as they move. We used a multiple object tracking task, in which younger and older adults were asked to keep track of moving target objects that moved randomly in the visual field among irrelevant distractor objects. By recording the brain's electrophysiological responses during the tracking period, we were able to delineate neural processing for targets and distractors at early stages of visual processing (~100-300 msec). Older adults showed less selective attentional modulation in the early phase of the visual P1 component (100-125 msec) than younger adults, indicating that early selection is compromised in old age. However, with a 25-msec delay relative to younger adults, older adults showed distinct processing of targets (125-150 msec), that is, a delayed yet intact attentional modulation. The magnitude of this delayed attentional modulation was related to tracking performance in older adults. The amplitude of the N1 component (175-210 msec) was smaller in older adults than in younger adults, and the target amplification effect of this component was also smaller in older relative to younger adults. Overall, these results indicate that normal aging affects the efficiency and timing of early visual processing during multiple object tracking.

Compensation through increased functional connectivity: neural correlates of inhibition in old and young

With increasing age, people experience more difficulties with suppressing irrelevant information, which may have a major impact on cognitive functioning. The extent of decline of inhibitory functions with age is highly variable between individuals. In this study, we used ERPs and phase locking analyses to investigate neural correlates of this variability in inhibition between individuals. Older and younger participants performed a selective attention task in which relevant and irrelevant information was presented simultaneously. The participants were split into high and low performers based on their level of inhibition inefficiency, that is, the slowing of RTs induced by information that participants were instructed to ignore. P1 peak amplitudes were larger in low performers than in high performers, indicating that low performers were less able to suppress the processing of irrelevant stimuli. Phase locking analyses were used as a measure of functional connectivity. Efficient inhibition in both age groups was related to the increased functional connectivity in the alpha band between frontal and occipito-parietal ROIs in the prestimulus interval. In addition, increased power in the alpha band in occipito-parietal ROIs was related to better inhibition both before and after stimulus onset. Phase locking in the upper beta band before and during stimulus presentation between frontal and occipito-parietal ROIs was related to a better performance in older participants only, suggesting that this is an active compensation mechanism employed to maintain adequate performance. In addition, increased top-down modulation and increased power in the alpha band appears to be a general mechanism facilitating inhibition in both age groups.

Khat use is associated with increased response conflict in humans

OBJECTIVE

Khat consumption has become a worldwide phenomenon broadening from Eastern Africa and the south west of the Arabian Peninsula to ethnic communities in the rest of the world. Only few studies have systematically looked into cognitive impairments in khat users. We studied whether khat use is associated with changes in the emergence and resolution of response conflict, a central cognitive control function.

METHOD

Khat users (n = 16) and khat-free controls (n = 16) were matched in terms of sex, ethnicity, socio-economical situation, age, alcohol and cannabis consumption, and IQ (Raven's Progressive Matrices). Groups were tested on response conflict, as measured by the Simon task.

RESULTS

Khat users performed significantly slower than controls and were more strongly affected by stimulus-induced response conflict.

CONCLUSIONS

Khat use is associated with specific impairments in behavioral control: general slowing and less efficient resolution of response conflicts, which is likely to impair decision making in everyday life.

Functional definition of the N450 event-related brain potential marker of conflict processing: a numerical stroop study

Background

Several conflict processing studies aimed to dissociate neuroimaging phenomena related to stimulus and response conflict processing. However, previous studies typically did not include a paradigm-independent measure of either stimulus or response conflict. Here we have combined electro-myography (EMG) with event-related brain potentials (ERPs) in order to determine whether a particularly robust marker of conflict processing, the N450 ERP effect usually related to the activity of the Anterior Cingulate Cortex (ACC), is related to stimulus- or to response-conflict processing. EMG provided paradigm-independent measure of response conflict. In a numerical Stroop paradigm participants compared pairs of digits and pressed a button on the side where they saw the larger digit. 50% of digit-pairs were preceded by an effective cue which provided accurate information about the required response. 50% of trials were preceded by a neutral cue which did not communicate the side of response.

Results

EMG showed that response conflict was significantly larger in neutrally than in effectively cued trials. The N450 was similar when response conflict was high and when it was low.

Conclusions

We conclude that the N450 is related to stimulus or abstract, rather than to response conflict detection/resolution. Findings may enable timing ACC conflict effects.

On why not to rush older adults--relying on reactive cognitive control can effectively reduce errors at the expense of slowed responses

According to the dual-mechanisms of cognitive control framework (DMC), older adults rely predominantly on reactive as opposed to proactive control. As a result, we expected elevated response conflict for older relative to younger adults with increasing task difficulty. Response-locked ERP activity was examined separately for fast and slow responses (representing proactive and reactive control, respectively) at low, medium, and high levels of difficulty. Older adults recruited reactive control more often than the young, as reflected by increased behavioral costs and enhanced pre-response negativity (PRN). No age differences in conflict detection (medial frontal negativity, MFN) were evident at low levels of difficulty, but response conflict increased along with difficulty for older adults. These data provide empirical support for the DMC suggesting that aging is associated with a less efficient reactive-control mode of processing.

Mismatch and Conflict: Neurophysiological and Behavioral Evidence for Conflict Priming

Conflict-related cognitive processes are critical for adapting to sudden environmental changes that confront the individual with inconsistent or ambiguous information. Thus, these processes play a crucial role to cope with daily life. Generally, conflicts tend to accumulate especially in complex and threatening situations. Therefore, the question arises how conflict-related cognitive processes are modulated by the close succession of conflicts. In the present study, we investigated the effect of interactions between different types of conflict on performance as well as on electrophysiological parameters. A task-irrelevant auditory stimulus and a task-relevant visual stimulus were presented successively. The auditory stimulus consisted of a standard or deviant tone, followed by a congruent or incongruent Stroop stimulus. After standard prestimuli, performance deteriorated for incongruent compared to congruent Stroop stimuli, which were accompanied by a widespread negativity for incongruent versus congruent stimuli in the event-related potentials (ERPs). However, after deviant prestimuli, performance was better for incongruent than for congruent Stroop stimuli and an additional early negativity in the ERP emerged with a fronto-central maximum. Our data show that deviant auditory prestimuli facilitate specifically the processing of stimulus-related conflict, providing evidence for a conflict-priming effect.

Age-related changes in early novelty processing as measured by ERPs

This study investigated age-related changes in the early processing of novel visual stimuli using ERPs. Well-matched old (n=30), middle-aged (n=30), and young (n=32) subjects were presented standard, target/rare, and perceptually novel visual stimuli under Attend and Ignore conditions. Our results suggest that the anterior P2 component indexes the motivational salience of a stimulus as determined by either task relevance or novelty. Its enhancement by focused attention does not decrease with age. Its responsiveness to novel stimuli is particularly striking in older adults. The age-related increase in the anterior P2 to novel visual stimuli does not appear to be due to impaired inhibitory control associated with aging. Rather, the enhanced anterior P2 to novel stimuli in older adults may be linked to age-related changes in the process of matching unusual visual stimuli to stored representations, which is indexed by the temporally overlapping anterior N2 component whose amplitude substantially decreases with age.

Event-related potentials with the Stroop colour-word task: timing of semantic conflict

Event-Related Potentials (ERPs) elicited by congruent and incongruent colour-word stimuli of a Stroop paradigm, in a task in which participants were required to judge the congruence/incongruence of the two dimensions of the stimuli, were recorded in order to study the timing of the semantic conflict. The reaction time to colour-word incongruent stimuli was significantly longer than the reaction time to congruent stimuli (the Stroop effect). A temporal Principal Components Analysis was applied to the data to identify the ERP components. Three positive components were identified in the 300-600 ms interval in response to the congruent and incongruent stimuli: First P3, P3b and PSW. The factor scores corresponding to the First P3 and P3b components were significantly smaller for the incongruent stimuli than for the congruent stimuli. No differences between stimuli were observed in the factor scores corresponding to the PSW or in the ERP latencies. We conclude that the temporal locus of the semantic conflict, which intervenes in generating the Stroop effect, may occur within the time interval in which the First P3 and P3b components are identified, i.e. at approximately 300-450 ms post-stimulus. We suggest that the semantic conflict delays the start of the response selection process, which explains the longer reaction time to incongruent stimuli.

Enhanced and bilateralized visual sensory processing in the ventral stream may be a feature of normal aging

Evidence has emerged for age-related amplification of basic sensory processing indexed by early components of the visual evoked potential (VEP). However, since these age-related effects have been incidental to the main focus of these studies, it is unclear whether they are performance dependent or alternately, represent intrinsic sensory processing changes. High-density VEPs were acquired from 19 healthy elderly and 15 young control participants who viewed alphanumeric stimuli in the absence of any active task. The data show both enhanced and delayed neural responses within structures of the ventral visual stream, with reduced hemispheric asymmetry in the elderly that may be indicative of a decline in hemispheric specialization. Additionally, considerably enhanced early frontal cortical activation was observed in the elderly, suggesting frontal hyper-activation. These age-related differences in early sensory processing are discussed in terms of recent proposals that normal aging involves large-scale compensatory reorganization. Our results suggest that such compensatory mechanisms are not restricted to later higher-order cognitive processes but may also be a feature of early sensory-perceptual processes.