Functional electrical stimulation to enhance reactive balance among people with hemiparetic stroke

BACKGROUND

Individuals with stroke demonstrate a twofold higher fall incidence compared to healthy counterparts, potentially associated with deficits in reactive balance control, which is crucial for regaining balance from unpredictable perturbations to the body. Moreover, people with higher stroke-related motor impairment exhibit greater falls and cannot recover balance during higher perturbation intensities. Thus, they might need supplemental agents for fall prevention or even to be included in a perturbation-based protocol. Functional electrical stimulation is a widely used clinical modality for improving gait performance; however, it remains unknown whether it can enhance or interfere with reactive balance control.

METHODS

We recruited twelve ambulatory participants with hemiparetic stroke (61.48 ± 6.77 years) and moderate-to-high motor impairment (Chedoke-McMaster Stroke Leg Assessment ≤ 4/7). Each participant experienced 4 unpredicted paretic gait-slips, with and without functional electrical stimulation (provided 50-500 ms after perturbation) in random order. The paretic quadriceps muscle group was chosen to receive electrical stimulation, considering the role of support limb knee extensors for preventing limb-collapse. Outcomes including primary (laboratory falls), secondary (reactive stability, vertical limb support) and tertiary (compensatory step length, step initiation, execution time) measures were compared between the two conditions.

RESULTS

Participants demonstrated fewer falls, higher reactive stability, and higher vertical limb support (p < 0.05) following gait-slips with functional electrical stimulation compared to those without. This was accompanied by reduced step initiation time and a longer compensatory step (p < 0.05).

CONCLUSION

The application of functional electrical stimulation to paretic quadriceps following gait-slips reduced laboratory fall incidence with enhanced reactive balance outcomes among people with higher stroke-related motor impairment. Our results lay the preliminary groundwork for understanding the instantaneous neuromodulatory effect of functional electrical stimulation in preventing gait-slip falls, future studies could test its therapeutic effect on reactive balance. Clinical registry number: NCT04957355.

Reactive and proactive control processes in voluntary task choice

Deciding which task to perform when multiple tasks are available can be influenced by external influences in the environment. In the present study, we demonstrate that such external biases on task-choice behavior reflect reactive control adjustments instead of a failure in control to internally select a task goal. Specifically, in two experiments we delayed the onset of one of two task stimuli by a short (50 ms), medium (300 ms), or long (1,000 ms) stimulus-onset asynchrony (SOA) within blocks while also varying the relative frequencies of short versus long SOAs across blocks (i.e., short SOA frequent vs. long SOA frequent). Participants' task choices were increasingly biased towards selecting the task associated with the first stimulus with increasing SOAs. Critically, both experiments also revealed that the short-to-medium SOA bias was larger in blocks with more frequent long SOAs when participants had limited time to prepare for an upcoming trial. When time to select an upcoming task was extended in Experiment 2, this interaction was not significant, suggesting that the extent to which people rely on reactive control adjustments is additionally modulated by proactive control processes. Thus, the present findings also suggest that voluntary task choices are jointly guided by both proactive and reactive processes, which are likely to adjust the relative activation of different task goals in working memory.

The location-specific proportion congruence effect: Are left/right locations special?

People reactively adjust attentional control based on the history of conflict experiences at different locations resulting in location-specific proportion compatibility (LSPC) effects. Weidler et al. (2022, Journal of Experimental Psychology: Human Perception and Performance, 48[4], 312-330) found that LSPC effects were larger when stimuli were presented on the horizontal axis (i.e., locations to left and right of fixation) compared with the vertical axis (i.e., locations above and below fixation). They proposed and provided initial evidence suggesting left/right locations may represent a special design feature that leads to stronger LSPC effects (i.e., horizontal precedence account). However, their use of horizontally oriented flanker stimuli, which required participants to traverse through the distracting flankers to select the central target selectively in the horizontal axis condition, may have contributed to the horizontal advantage they observed (i.e., gaze path account). The present study tested competing predictions of these two accounts. Experiment 1 used vertically oriented flanker stimuli and compared the findings with Weidler et al. The LSPC effect was larger for vertically oriented stimuli on the vertical axis, and horizontally oriented stimuli on the horizontal axis, supporting the gaze path account. Experiment 2 used flanker stimuli that required participants to traverse through distracting flankers regardless of the axis on which stimuli were presented. The LSPC effect was equivalent between the vertical axis and horizontal axis conditions. These results further supported the gaze path account and suggest that the critical design feature for amplifying LSPC effects is not left/right locations per se, but rather use of stimuli/axis combinations that encourage processing of the distractor dimension.

Contextual adaptation of cognitive flexibility in kindergartners and fourth graders

This study investigated the development of children's ability to find the optimal balance between flexibility and stability as a function of the frequency of required task switches. This question was addressed in two situations contrasting the dynamics of engagement of reconfiguration processes (reactive vs. proactive). A cued task-switching paradigm was presented to kindergartners and fourth graders, who are known to differ in their preferential mode of control engagement. Flexibility adaptation was examined through the modulation of switching costs by switch proportion, the so-called list-wide switch proportion (LWSP) effect. When the situation forced the use of reactive control (Experiment 1: simultaneous presentation of the cue and the stimulus), we found the LWSP effect with a greater magnitude in kindergartners than in fourth graders. In the situation inducing proactive control (Experiment 2: task cue presented before and until the stimulus), flexibility adaptation was obtained when error rates were considered but not response times. By demonstrating that even young children are capable of flexibility adaptation to contextual demands, these findings support the hypothesis that implicitly triggered adaptation of control may develop as early as the end of the preschool years despite the immaturity of cognitive control during this period.

A process-specific approach in the study of normal aging deficits in cognitive control: What deteriorates with age?

Bearing in mind that cognitive control is a complex function that includes several processes, it is not clear exactly which ones deteriorate with age. In fact, controversial results have been found. For example, some studies indicate that age-related deficits are observed in proactive and not in reactive control, others show that it is reactive control that is impaired and not proactive control, and some studies find no deficits at all (e.g., Kopp, Lange, Howe, & Wessel, 2014; Xiang et al., 2016). One possible reason is that the contribution of different processes to the deterioration of cognitive control was investigated separately, i.e., without testing all processes within the same paradigm. Therefore, the main goal of the present experiment was to study the impact of normal aging on several processes related to cognitive control within the same task, which included both Simon and Spatial Stroop trials. The study focused on the following processes: generation of conflict measured by automatic response capture (i.e., stronger task-irrelevant information processing compared to task-relevant information processing); conflict detection; and control implementation (which can be reactive control, both within trials and across trials, and proactive control, as a task-set strategy). The results showed larger automatic response capture for older adults when facing a stimulus-response conflict (Simon) but not a stimulus-stimulus conflict (Spatial Stroop). Similarly, older adults also showed larger detection effects for both conflicts. However, regarding control implementation, they only showed difficulties in inhibiting the early automatic response capture (within-trial reactive control) but not reactive control across trials or proactive control. In conclusion, it seems that older adults are more affected by the presence of task-irrelevant information, especially when it comes to resolving stimulus-response conflict. However, they showed no impairments in their ability to implement cognitive control both across trials and as a task-set strategy.

Both task-irrelevant and task-relevant information trigger reactive conflict adaptation in the item-specific proportion-congruent paradigm

Adapting attention flexibly is a fundamental ability of the human control system. In the color-word Stroop task, for example, congruency effects are typically smaller for colors and words that appear mainly in incongruent stimuli (mostly-incongruent items) than for colors and words that appear mainly in congruent stimuli (mostly-congruent items). At least part of this item-specific proportion-congruent (ISPC) effect is due to a process of reactive conflict adaptation that affords higher selectivity (i.e., more efficient selection of task-relevant information) when a specific stimulus is presented that is frequently associated in the experiment with conflicting task-irrelevant information. What is unclear, however, is whether, normally, this stimulus-specific adaptation is triggered by the task-relevant component, the task-irrelevant component, or both components of the stimulus. In two experiments, using modified color-word (Experiment 1) and spatial (Experiment 2) Stroop tasks that allowed task-relevant and task-irrelevant triggering processes to be dissociated, we found that the two processes have approximately equivalent impacts. Because these results were obtained in experiments imposing no limitations on the processes potentially contributing to the ISPC effect, these results challenge claims that the ISPC effect involves conflict-adaptation processes only in special situations. The ISPC effect may involve conflict-adaptation processes in most situations, with both task-relevant and task-irrelevant information triggering such processes.

The choice of reference point for computing sagittal plane angular momentum affects inferences about dynamic balance

Background

Measures of whole-body angular momentum in the sagittal plane are commonly used to characterize dynamic balance during human walking. To compute angular momentum, one must specify a reference point about which momentum is calculated. Although biomechanists primarily compute angular momentum about the center of mass (CoM), momentum-based controllers for humanoid robots often use the center of pressure. Here, we asked if the choice of the reference point influences interpretations of how dynamic balance is controlled in the sagittal plane during perturbed walking.

Methods

Eleven healthy young individuals walked on a dual-belt treadmill at their self-selected speed. Balance disturbances were generated by treadmill accelerations of varying magnitudes and directions. We computed angular momentum about two reference points: (1) the CoM or (2) the leading edge of the base of support and then projected it along the mediolateral axes that pass through either of the reference points as the sagittal plane angular momentum. We also performed principal component analysis to determine if the choice of reference point influences our interpretations of how intersegmental coordination patterns contribute to perturbation recovery.

Results

We found that the peak angular momentum was correlated with perturbation amplitude and the slope of this relationship did not differ between reference points. One advantage of using a reference point at the CoM is that one can easily determine how the momenta from contralateral limbs, such as the left and right legs, offset one another to regulate the whole-body angular momentum. Alternatively, analysis of coordination patterns referenced to the leading edge of the base of support may provide more insight into the inverted-pendulum dynamics of walking during responses to sudden losses of balance.

Impaired cognitive control in patients with brain tumors

Though the assessment of cognitive functions is proven to be a reliable prognostic indicator in patients with brain tumors, some of these functions, such as cognitive control, are still rarely investigated. The objective of this study was to examine proactive and reactive control functions in patients with focal brain tumors and to identify lesioned brain areas more at "risk" for developing impairment of these functions. To this end, a group of twenty-two patients, candidate to surgery, were tested with an AX-CPT task and a Stroop task, along with a clinical neuropsychological assessment, and their performance was compared to that of a well-matched healthy control group. Although overall accuracy and response times were similar for patients and control groups, the patient group failed more on the BX trials of the AX-CPT task and the incongruent trials of the Stroop task, specifically. Behavioral results were associated with the damaged brain areas, mostly distributed in right frontal regions, by means of a lesion-symptom mapping multivariate approach. This analysis showed that a white matter cluster in the right prefrontal area was associated with lower d'-context values on the AX-CPT, which reflect the fact that these patients rely more on later information (reactive processes) to respond to unexpected and conflicting stimuli, than on earlier contextual cues (proactive processes). Taken together, these results suggest that patients with brain tumors present an unbalance between proactive and reactive control strategies in more interfering conditions, in association with right prefrontal white matter lesions.

Developmental Changes in the Association Between Cognitive Control and Anxiety

Anxiety has been associated with reliance on reactive (stimulus-driven/reflexive) control strategies in response to conflict. However, this conclusion rests primarily on indirect evidence. Few studies utilize tasks that dissociate the use of reactive ('just in time') vs. proactive (anticipatory/preparatory) cognitive control strategies in response to conflict, and none examine children diagnosed with anxiety. The current study utilizes the AX-CPT, which dissociates these two types of cognitive control, to examine cognitive control in youth (ages 8-18) with and without an anxiety diagnosis (n = 56). Results illustrate that planful behavior, consistent with using a proactive strategy, varies by both age and anxiety symptoms. Young children (ages 8-12 years) with high anxiety exhibit significantly less planful behavior than similarly-aged children with low anxiety. These findings highlight the importance of considering how maturation influences relations between anxiety and performance on cognitive-control tasks and have implications for understanding the pathophysiology of anxiety in children.

Reactive and proactive cognitive control as underlying processes of number processing in children

Cognitive control is crucial to resolve conflict in tasks such as the flanker task. Reactive control is used when conflict is rare, whereas proactive control is more efficient in situations where conflict is frequent. Macizo and Herrera (Psychological Research, 2013, Vol. 77, pp. 651-658) found that these two control processes can also underlie two-digit number comparison in adults. Specifically, they observed that the unit-decade compatibility effect decreased in a block containing many conflict trials as compared with a block containing few conflict trials (i.e., a list-wide proportion congruency effect). In the current study, we assessed whether this finding also applies to children (7-, 9-, and 11-year-olds). Participants performed a flanker task and a two-digit number comparison task. In both tasks, the proportion of conflict was manipulated (80% vs. 20%). Results from the flanker task showed a typical list-wide proportion congruency effect in reaction times in all participating age groups. In the number comparison task, we observed list-wide proportion congruency effects in both reaction times and error rates, which did not interact with age. Our findings support the assumption that children as young as 7 years can effectively use proactive and reactive control strategies. We showed that this effect is not limited to standardized artificial laboratory tasks, such as the flanker task, but also underlies more daily life tasks, such as the processing of Arabic numbers.

Dissociation of Proactive and Reactive Cognitive Control in Individuals with Schizotypy: An Event-Related Potential Study

OBJECTIVE

Patients with schizophrenia and individuals with schizotypy, a subclinical group at risk for schizophrenia, have been found to have impairments in cognitive control. The Dual Mechanisms of Cognitive Control (DMC) framework hypothesises that cognitive control can be divided into proactive and reactive control. However, it is unclear whether individuals with schizotypy have differential behavioural impairments and neural correlates underlying these two types of cognitive control.

METHOD

Twenty-five individuals with schizotypy and 26 matched healthy controls (HCs) completed both reactive and proactive control tasks with electroencephalographic data recorded. The proportion of congruent and incongruent trials was manipulated in a classic colour-word Stroop task to induce proactive or reactive control. Proactive control was induced in a context with mostly incongruent (MI) trials and reactive control in a context with mostly congruent (MC) trials. Two event-related potential (ERP) components, medial frontal negativity (MFN, associated with conflict detection) and conflict sustained potential (conflict SP, associated with conflict resolution) were examined.

RESULTS

There was no significant difference between the two groups in terms of behavioural results. In terms of ERP results, in the MC context, HC exhibited significantly larger MFN (360-530 ms) and conflict SP (600-1000 ms) amplitudes than individuals with schizotypy. The two groups did not show any significant difference in MFN or conflict SP in the MI context.

CONCLUSIONS

The present findings provide initial evidence for dissociation of neural activation between proactive and reactive cognitive control in individuals with schizotypy. These findings help us understand cognitive control deficits in the schizophrenia spectrum.

The dynamic monitoring and control mechanism in problem solving: Evidence from theta and alpha oscillations

Although both originality and value are considered necessary criteria to identify creative ideas, little is known about how original and valuable ideas are generated in the human brain. To reveal how people monitor and control ongoing processing in the pursuit of original and valuable ideas, high-density electroencephalography (EEG) was used to record electrophysiological signals when participants were performing chunk decomposition tasks via novel-appropriate, novel-inappropriate, ordinary-appropriate and ordinary-inappropriate pathways. The results showed that approximately 100 ms after the problem was presented, novel pathways showed increased theta synchronization in the frontal sites compared to ordinary pathways. Novel pathways were associated with increased alpha desynchronization over the entire brain scale. These theta and alpha oscillations likely indicated rapid monitoring and effective control of novel processing in thinking. In the latter stages of problem solving, particularly during the 2000-2600-ms intervals, increased theta synchronization with decreased alpha desynchronization was found between novel-inappropriate and novel-appropriate pathways, which likely indicated slow monitoring and less control of inappropriate processing in novel thinking. The findings demonstrated the dynamic monitoring and control mechanism in the pursuit of original and valuable ideas.

Cognitive control in obsessive-compulsive disorder (OCD): Proactive control adjustments or consistent performance?

Cognitive control is often parsed into proactive and reactive control components. In proactive control, task- and goal-relevant information is utilized in a top-down manner to improve performance, while reactive control is a late-response corrective mechanism that occurs after conflict or errors. We tested whether people with obsessive-compulsive disorder (OCD) would show specific proactive control dysfunction in 31 individuals with OCD and 30 psychiatrically-healthy controls. We employed two tasks that differentiate proactive and reactive cognitive control processes: the cued-Stroop and the AX version of a continuous performance task (AX-CPT). There was a 1s or 5s delay between the cue and probe for both tasks to allow for implementation of proactive control processes. Participants also completed a neuropsychological test battery and mood and symptom severity self-report questionnaires. Although there were group-level differences in OCD severity and depression/anxiety symptoms, there were no significant differences in response times (RT) and error rates between groups for delay or condition for the cued-Stroop or for the AX-CPT, indicating similar performance in implementing proactive control strategies. There were also no significant differences between OCD and control participants on neuropsychological test performance. Results suggest a convergence of evidence wherein individuals with OCD are not showing disproportionately altered proactive control abilities.

The influence of monetary reward on proactive and reactive control in adolescent males

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Reward reduced RT interference during reactive control, but increased RT interference during proactive control in male adolescents.

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Increased reward-related cue-locked theta power was associated with increased RT interference on proactive trials.

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Increased reward-related stimulus-locked theta inter-channel phase synchrony was related to facilitated performance on proactive trials.

Adolescence is marked by increased reward-seeking, which can alter cognitive control abilities. Previous research found that rewards actually improve cognitive control in children, adolescents, and adults, but these studies only investigated reactive control. The goal of the current study was to elucidate reward’s influence on both proactive and reactive control during adolescence. To this end, 68 (Mean age = 13.61, SD = 2.52) male adolescents completed a rewarded cued flanker paradigm while electroencephalogram (EEG) was collected. Theta power and inter-channel phase synchrony, both implicated in cognitive control, were quantified after cues and stimuli to understand their role during reward-cognitive control interactions. The data suggest that reward reduced interference during reactive control; however, reward increased interference during proactive control in this sample of adolescent males. Reward-related increases in cue-locked theta power predicted more reward-related RT interference on proactive trials. In contrast, increases in stimulus-locked theta ICPS were associated with better performance on rewarded proactive trials. The pattern of results show that reward differentially impacted proactive and reactive control in adolescence, which may have implications for the increased risk-taking behaviors observed during adolescence.

Maintaining sagittal plane balance compromises frontal plane balance during reactive stepping in people post-stroke

BACKGROUND

Maintaining balance in response to perturbations during walking often requires the use of corrective responses to keep the center of mass within the base of support. The relationship between the center of mass and base of support is often quantified using the margin of stability. Although people post-stroke increase the margin of stability following perturbations, control deficits may lead to asymmetries in regulation of margins of stability, which may also cause maladaptive coupling between the sagittal and frontal planes during balance-correcting responses.

METHODS

We assessed how paretic and non-paretic margins of stability are controlled during recovery from forward perturbations and determined how stroke-related impairments influence the coupling between the anteroposterior and mediolateral margins of stability. Twenty-one participants with post-stroke hemiparesis walked on a treadmill while receiving slip-like perturbations on both limbs at foot-strike. We assessed anteroposterior and mediolateral margins of stability before perturbations and during perturbation recovery.

FINDINGS

Participants walked with smaller anteroposterior and larger mediolateral margins of stability on the paretic versus non-paretic sides. When responding to perturbations, participants increased the anteroposterior margin of stability bilaterally by extending the base of support and reducing the excursion of the extrapolated center of mass. The anteroposterior and mediolateral margins of stability in the paretic limb negatively covaried during reactive steps such that increases in anteroposterior were associated with reductions in mediolateral margins of stability.

INTERPRETATION

Balance training interventions to reduce fall risk post-stroke may benefit from incorporating strategies to reduce maladaptive coupling of frontal and sagittal plane stability.

Impaired Frontal Midline Theta During Periods of High Reaction Time Variability in Schizophrenia

BACKGROUND

Impairment in cognitive control is one of the most significant cognitive deficits in schizophrenia. Although it has generally been associated with altered engagement of lateral and medial prefrontal cortices, how attention fluctuations affect this engagement is still not known. In this context, we explored sustained (or proactive) and transient (or reactive) control engagement by investigating frontal theta-band oscillations during periods of low- and high-performance instability, assumed to represent intraindividual attentional fluctuations.

METHODS

A total of 25 patients with schizophrenia (16 males) and 25 healthy matched control subjects (18 males) performed a long-sustained Go/NoGo task coupled with electroencephalographic recording. Proactive control was explored through frontal lateral theta during trial-by-trial conflict (Go N-1/Go N+1), whereas reactive control was explored through frontal midline theta and the N2 component during current-trial conflict (Go/NoGo). Variance in the time course of reaction time (RT) was computed to identify periods of low and high RT variability in each subject.

RESULTS

Patients with schizophrenia exhibited no frontal lateral theta activity regardless of the RT variability periods, whereas in control subjects, this activity was preserved only during periods of low RT variability (less error prone). During these periods, patients exhibited preserved midline frontal theta activity and N2. However, during high RT variability periods (more error prone), the midline theta activity was impaired in patients but preserved in control subjects.

CONCLUSIONS

Our results reveal that the efficient engagement of reactive control in patients with schizophrenia and of proactive control in control subjects was state dependent. The findings highlight the importance of accounting for attentional fluctuations when investigating cognitive control impairment in schizophrenia.

A cross-sectional study on interference control: age affects reactive control but not proactive control

Background

Working memory updating (WMU), a controlled process to continuously adapt to the changing task demand and environment, is crucial for cognitive executive function. Although previous studies have shown that the elderly were more susceptible to cognitive interference than the youngsters, the picture of age-related deterioration of WMU is incomplete due to lack of study on people at their middle ages. Thus, the present study investigated the impact of age on the WMU among adults by a cross-sectional design to verify whether inefficiency interference control accounts for the aging of WMU.

Methods

In total, 112 healthy adults were recruited for this study; 28 old adults (21 female) ranging from 60 to 78 years of age; 28 middle-age adults (25 female) ranging from 45 to 59 years of age; 28 adults (11 female) ranging from 26 to 44 years of age; and 28 young adults (26 female) ranging from 18 to 25 years of age. Each participant completed a 1-back task. The inverse efficiency score was calculated in various sequences of three trials in a row to quantify the performance of WMU for adults of various ages.

Results

Inverse efficiency score of both young groups (young adult and adult) were significantly shorter than the old group in both Repeat-Alternate (RA, including □□○ and ○○□) and Alternate-Alternate (AA, including ○□○ and □○□) sequential patterns and they were additionally better than the middle-age group in AA sequential pattern.

Conclusion

With the increase of difficulty in the task, the difference in reactive interference control between young and middle age was gradually revealed, while the difference between young and old remained to apparent. The degradation of WMU aging may begin from middle-age and presents selective impairment in that only reactive interference control, but not proactive interference control, shows pronounced age-related decline. The preliminary results can inform future studies to further explore the whole lifespan trajectories of cognitive functions.

Age-related changes in neural mechanisms of prospective memory

The capability to remember and execute intentions in the future - termed prospective memory (PM) - may be of special significance for older adults to enable successful completion of important activities of daily living. Despite the importance of this cognitive function, mixed findings have been obtained regarding age-related decline in PM, and, currently, there is limited understanding of potential contributing mechanisms. In the current study, older (N=41) and younger adults (N=47) underwent task-functional MRI during performance of PM conditions that encouraged either spontaneous retrieval (Focal) or sustained attentional monitoring (Non-focal) to detect PM targets. Older adults exhibited a reduction in PM-related sustained activity within the anterior prefrontal cortex (aPFC) and associated dorsal frontoparietal cognitive control network, due to an increase in non-specific sustained activation in (no-PM) control blocks (i.e., an age-related compensatory shift). Transient PM-trial specific activity was observed in both age groups within a ventral parietal memory network that included the precuneus. However, within a left posterior inferior parietal node of this network, transient PM-related activity was selectively reduced in older adults during the non-focal condition. These age differences in sustained and transient brain activity statistically mediated age-related declines in PM performance, and were potentially linked via age-related changes in functional connectivity between the aPFC and precuneus. Together, they support an account consistent with the Dual Mechanisms of Control framework, in which age-related PM declines are due to neural mechanisms that support proactive cognitive control processes, such as sustained attentional monitoring, while leaving reactive control mechanisms relatively spared.

Context-dependent modulation of cognitive control involves different temporal profiles of fronto-parietal activity

To efficiently deal with quickly changing task demands, we often need to organize our behaviour on different time scales. For example, to ignore irrelevant and select relevant information, cognitive control might be applied in reactive (short time scale) or proactive (long time scale) mode. These two control modes play a pivotal role in cognitive-neuroscientific theorizing but the temporal dissociation of the underlying neural mechanisms is not well established empirically. In this fMRI study, a cognitive control task was administered in contexts with mainly congruent (MC) and mainly incongruent (MI) trials to induce reactive and proactive control, respectively. Based on behavioural profiles, we expected cognitive control in the MC context to be characterized by transient activity (measured on-trial) in task-relevant areas. In the MI context, cognitive control was expected to be reflected in sustained activity (measured in the intertrial interval) in similar or different areas. Results show that in the MC context, on-trial transient activity (incongruent - congruent trials) was increased in fronto-parietal areas, compared to the MI context. These areas included dorsolateral prefrontal cortex (dlPFC) and intraparietal sulcus (IPS). In the MI context, sustained activity in similar fronto-parietal areas during the intertrial interval was increased, compared to the MC context. These results illuminate how context-dependent reactive and proactive control subtend the same brain areas but operate on different time scales.

Reactive and proactive control mechanisms of response inhibition in gambling disorder

Response inhibition, one component of cognitive control, refers to the ability to inhibit automatic responses and has been found to be impaired in gambling disorder. Recent models of cognitive control distinguish between two mechanisms: reactive control, the ability to stop in response to a stop-stimulus, and proactive control, the ability to anticipate and prepare for a stop. Previous studies have primarily focused on reactive modes of control in gambling disorder. The aim of the current study was to assess both reactive and proactive modes of response inhibition in individuals with gambling disorder (n = 27) and community controls (n = 21) using a variant of the stop-signal task. Second, the relationship between trait impulsivity, and reactive and proactive control was examined. No group differences in reactive or proactive control were found. However, premeditation, one domain of trait impulsivity, was associated with worse proactive control in the gambling group. These results suggest that difficulties with response inhibition may not be a core deficit in all forms of gambling disorder. Future research should continue to develop and test tasks that involve cognitive control processes in different presentations of gambling disorder.

Older adults exhibit variable responses in stepping behaviour following unexpected forward perturbations during gait initiation

With the socioeconomic burden associated with falls expected to rise as the average age of the Canadian population increases, research is needed to elucidate the nature of postural responses generated by older adults (OA) following a posture-destabilizing event. This knowledge is even more imperative for novel and difficult tasks, such as gait initiation (GI), a task known to pose a postural threat to stability for OA. A common technique to regain stability following an unexpected perturbation is reactive stepping. A deficiency in the execution of a reactive control strategy following a destabilizing event may be the cause of many unexpected falls in OA. The purpose of this study is to explore age related changes in the nature of these responses during a challenging GI task combined with an unexpected forward perturbation of the support surface. A total of 18 young adults (YA) and 16 OA performed 36 trials containing 20 unexpected perturbations. We calculated step width, length, time and COM velocity in the first unperturbed step and the second perturbed step. Results revealed that, during unperturbed GI, OA had a reduced forward velocity and took shorter, faster steps. Following forward perturbations, OA altered stepping patterns, perhaps to reduce single support duration, via reduced base of support and shorter step length compared to YA. Additionally, OA executed both forward and backwards directed steps however YA only generated forward steps. Regression analyses revealed that reduced forward velocity was predictive of step direction; which is possibly an unfavorable motor control strategy as OA who walk slower generated a posterior directed step immediately following the perturbation. This strategy is of concern as rapid responses by the trail limb are required to recover successfully, and these alterations may be associated with an elevated risk of falls.

Evidencing the developmental shift from reactive to proactive control in early childhood and its relationship to working memory

As they age, children tend to get more effective at regulating their behavior in complex situations; this improvement in cognitive control is often interpreted as a shift from predominantly reactive control to proactive control. There are three issues with this interpretation. First, hard evidence is lacking that younger children actually rely on reactive control. Second, the precise age range when such a shift would occur is still unclear. Third, the reasons for this shift have not been explored. In the current study, we tested the hypothesis that children under 5 years of age do rely on reactive control, that they progressively shift to proactive control with age, and that this shift is related to increases in working memory capacity (which is necessary for proactive control). Children aged 4 to 7 years performed a cognitive control task, the AX-CPT (AX-Continuous Performance Task), as well as verbal and visuospatial working memory tasks. Using the paradigmatic AX-CPT in this age range allowed us to observe, for the first time, an actual reactive pattern in children under 5 years of age. There was a progressive shift from reactive control to proactive control, with an estimated turning point between 5 and 6 years of age. The effect of age on proactive control was essentially shared with working memory capacity, confirming that these two cognitive processes develop in tandem.

Age-related alterations in reactive stepping following unexpected mediolateral perturbations during gait initiation

BACKGROUND

A common technique to regain stability following an unexpected perturbation is reactive stepping, aimed to control the accelerated center of mass (COM). Many older adults (OA) struggle to execute the fast, coordinated stepping strategy required to arrest COM movement within the base of support (BOS) during these unexpected events, likely due to age-related physiological declines. Recent ecological data also suggests that many falls in OA occur due to errors in transferring or shifting body weight during activities of daily living. The present study utilized gait initiation, which requires a coordinated transition from quiet stance to dynamic gait, as an example of one of these difficult transitional movements.

RESEARCH QUESTION

Our goal was to combine this inherently unstable task, gait initiation, with an unexpected mediolateral (ML) perturbation of the support surface to examine age-related changes in reactive stepping patterns during a novel transitional gait task.

METHODS

A total of 18 young adults (YA) and 16 OA (>65 years) performed 35 trials containing 10 unexpected ML perturbations of the support surface. To quantify age-related differences, we calculated step width, length, time and COM velocity in the first two steps following the perturbation.

RESULTS

We observed that, in general, OA walked slower and took shorter, faster steps (reducing time in single support) compared to YA. Following the perturbation, OA altered their stepping patterns by reducing their BOS (more narrow step width compared to YA), and required more than the two steps used by YA to complete the goal-directed task.

SIGNIFICANCE

These age-related changes are concerning as a multi-step recovery strategy has been previously associated with an elevated risk of falls in OA.

Motor skill experience modulates executive control for task switching

This study aimed to investigate the effect of types of motor skills, including open and closed skills on enhancing proactive and reactive controls for task switching. Thirty-six athletes in open (n=18) or closed (n=18) sports and a control group (n=18) completed the task-switching paradigm and the simple reaction task. The task-switching paradigm drew on the proactive and reactive control of executive functions, whereas the simple reaction task assessed the processing speed. Significant Validity×Group effect revealed that the participants with open skills had a lower switch cost of response time compared to the other two groups when the task cue was 100% valid; whereas the participants regardless of motor skills had a lower switch cost of response time compared to the control group when the task cue was 50% valid. Hierarchical stepwise regression analysis further confirmed these findings. For the simple reaction task, there were no differences found among the three groups. These findings suggest that experience in open skills has benefits of promoting both proactive and reactive controls for task switching, which corresponds to the activity context exposed by the participants. In contrast, experience in closed skills appears to only benefit development of reactive control for task switching. The neural mechanisms for the proactive and reactive controls of executive functions between experts with open and closed skills call for future study.

Perceptual episodes, temporal attention, and the role of cognitive control: Lessons from the attentional blink

The ability to identify a target is usually hindered if it appears shortly after another target. This simple and somewhat intuitive observation is qualified by a multitude of unexpected findings and conflicting theories that originate from the attentional blink paradigm. In this review, the major results, implications, and outstanding questions that stem from the paradigm are presented and discussed. The extant literature suggests that when the temporal domain is densely stacked with numerous stimuli, the entities that underlie attentional selection and cognitive control are brief perceptual episodes. Specifically, attention is deployed over an interval that frequently encompasses several stimuli. Most theories agree that the length and boundaries of this interval are influenced by cognitive control mechanisms. However, there is little agreement as to the extent and nature of this influence. Some theories suggest that control is needed in order to initiate a temporally limited attentional response. Other theories argue that cognitive control is actively suppressing attentional mechanisms in order to terminate the perceptual episode. Another formulation suggests that both ends of the interval are partially controlled and that the exertion of control corresponds to the focusing of attention on a narrow interval. The contents of perceptual episodes, as well as their deficiencies, can shed light on the features that guide attentional deployment, the goals that guide cognitive control, and the interactions between these mechanisms. Electrophysiological recordings are extremely useful when one tries to pinpoint the timing of attentional selection. Other neural indicators can elucidate the factors that define perceptual episodes.

Testing the physiological plausibility of conflicting psychological models of response inhibition: A forward inference fMRI study

The neural mechanisms underlying response inhibition and related disorders are unclear and controversial for several reasons. First, it is a major challenge to assess the psychological bases of behaviour, and ultimately brain-behaviour relationships, of a function which is precisely intended to suppress overt measurable behaviours. Second, response inhibition is difficult to disentangle from other parallel processes involved in more general aspects of cognitive control. Consequently, different psychological and anatomo-functional models coexist, which often appear in conflict with each other even though they are not necessarily mutually exclusive. The standard model of response inhibition in go/no-go tasks assumes that inhibitory processes are reactively and selectively triggered by the stimulus that participants must refrain from reacting to. Recent alternative models suggest that action restraint could instead rely on reactive but non-selective mechanisms (all automatic responses are automatically inhibited in uncertain contexts) or on proactive and non-selective mechanisms (a gating function by which reaction to any stimulus is prevented in anticipation of stimulation when the situation is unpredictable). Here, we assessed the physiological plausibility of these different models by testing their respective predictions regarding event-related BOLD modulations (forward inference using fMRI). We set up a single fMRI design which allowed for us to record simultaneously the different possible forms of inhibition while limiting confounds between response inhibition and parallel cognitive processes. We found BOLD dynamics consistent with non-selective models. These results provide new theoretical and methodological lines of inquiry for the study of basic functions involved in behavioural control and related disorders.

Worry-inducing stimuli in an aversive Go/NoGo task enhance reactive control in individuals with lower trait-anxiety

This study relates predictions on reactive and proactive cognitive control to findings on anxious apprehension/worry and ERN/Ne. We investigated whether worry-inducing stimuli in an aversive performance setting lead to a more pronounced increase of the ERN/Ne in individuals with lower anxious apprehension/worry. We also explored the N2 amplitude in the context of worry-inducing stimuli. Fifty-eight participants performed an extended Go/NoGo task. A neutral or fearful face was presented at the beginning of each trial, with the fearful face as a worry-inducing, distracting stimulus. In an aversive feedback condition, aversive feedback was provided for false or too slow responses. We found a more pronounced decrease of the ERN/Ne after worry-inducing stimuli compared to neutral stimuli in participants with lower anxious apprehension/worry. Moreover, less pronounced N2 amplitudes were associated with shorter reaction times in the aversive feedback condition. Implications for future research on error monitoring and trait-anxiety are discussed.

Strategies for stimulus selective stopping in the elderly

This study consisted of two primary aims: (1) to determine if different age groups exhibited different strategies (based on their behavioral reaction time [RT] patterns) while performing a stop-signal task and (2) whether there were age-related differences in reactive and/or proactive control processes. Twenty-four younger adults (20-30years) and 24 older adults (61-76years) participated in this study. Participants performed a stop-signal task, which included a choice RT block, global stop-signal block, and stimulus-selective stop-signal block. Participants' strategies were classified using the Bayes factor to support or reject the null hypotheses at the individual level based on paired comparisons among the mean no-signal, signal-respond, and ignore RTs. We found that older adults used a similar pattern of strategies as younger adults in performing a stimulus-selective stop-signal task; most of them utilized either the Stop then Discriminate strategy or Discriminate then Stop strategy with dependency between go and stop processing. In addition, while older adults exhibited an impaired reactive control deficiency reflected on their increased stop-signal RTs in the stimulus-selective stop-signal task, they did not show an impaired proactive control process because their go trials' RT differences between the choice RT and stop-signal blocks did not differ significantly from those of young adults.

The impact of cognitive control on children's goal monitoring in a time-based prospective memory task

The present study investigated whether developmental changes in cognitive control may underlie improvements of time-based prospective memory. Five-, 7-, 9-, and 11-year-olds (N = 166) completed a driving simulation task (ongoing task) in which they had to refuel their vehicle at specific points in time (PM task). The availability of cognitive control resources was experimentally manipulated by imposing a secondary task that required divided attention. Children completed the driving simulation task both in a full-attention condition and a divided-attention condition where they had to carry out a secondary task. Results revealed that older children performed better than younger children on the ongoing task and PM task. Children performed worse on the ongoing and PM tasks in the divided-attention condition compared to the full-attention condition. With respect to time monitoring in the final interval prior to the PM target, divided attention interacted with age such that older children's time monitoring was more negatively affected by the secondary task compared to younger children. Results are discussed in terms of developmental shifts from reactive to proactive monitoring strategies.

Proactive and reactive control of movement are differently affected in Attention Deficit Hyperactivity Disorder children

Attention-Deficit/Hyperactivity Disorder children are impaired in the ability to interrupt an ongoing action in relation to a sudden change in the environment (reactive control, measured by stop signal reaction time, SSRT). Less investigated is the ability to control the response when it is known in advance that it will be required to stop (proactive control, measured by change in Reaction time, RT). The study is aimed at exploring both the reactive and the proactive inhibitory control in a group of ADHD children compared to a group of age-matched controls. ADHD children (N=28) and Controls (N=28) performed 4 tasks: 2 tasks required to respond to the appearance of the go-signals (go task and nostop task) and 2 tasks to respond to the go signals in a context in which sometimes a restrain or suppression of the response was required (go-nogo task and stop task). ADHD children showed a longer SSRT compared to controls. Both groups showed an increment in RT by comparing the go-nogo to the go task and an increment in RT and SD by comparing the stop to the nostop task. ADHD children showed higher intra-individual variability (SD) compared to controls only in the stop and nostop task. ADHD children showed impaired reactive control but preserved proactive control, and the physical appearance of the go signal affected their reaction times intra-individual variability. A comparison between the reactive and proactive controls helps in defining neuropsychological profiles of ADHD children and can inspires therapeutic behavioral-cognitive strategies for response control.

Impact of negative affectively charged stimuli and response style on cognitive-control-related neural activation: an ERP study

The canonical AX-CPT task measures two forms of cognitive control: sustained goal-oriented control ("proactive" control) and transient changes in cognitive control following unexpected events ("reactive" control). We modified this task by adding negative and neutral International Affective Picture System (IAPS) pictures to assess the effects of negative emotion on these two forms of cognitive control. Proactive and reactive control styles were assessed based on measures of behavior and electrophysiology, including the N2 event-related potential component and source space activation (Low Resolution Tomography [LORETA]). We found slower reaction-times and greater DLPFC activation for negative relative to neutral stimuli. Additionally, we found that a proactive style of responding was related to less prefrontal activation (interpreted to reflect increased efficiency of processing) during actively maintained previously cued information and that a reactive style of responding was related to less prefrontal activation (interpreted to reflect increased efficiency of processing) during just-in-time environmentally triggered information. This pattern of results was evident in relatively neutral contexts, but in the face of negative emotion, these associations were not found, suggesting potential response style-by-emotion interaction effects on prefrontal neural activation.