The unidirectional prosaccade switch-cost: Correct and error antisaccades differentially influence the planning times for subsequent prosaccades

Menstrual cycle status does not impact exercise-based changes in cerebral blood flow or executive function benefits

A single bout of exercise enhances executive function (EF) and may relate to an increase in cerebral blood flow (CBF). A limitation in the current literature is that biologically female participants are underrepresented given some evidence that changes in hormone levels across the menstrual cycle impact physiological and psychological variables. Here, biologically female participants completed separate single bouts of moderate intensity exercise (80% of estimated lactate threshold) during the follicular (FOL) and luteal (LUT) phases of their menstrual cycle. In addition, biologically male participants completed a same duration/intensity exercise session. Middle cerebral artery velocity (MCAv) was used to estimate CBF and pre- and postexercise EF was assessed via the antisaccade task. Results showed that resting MCAv was larger in the LUT than FOL phase; however, the exercise-mediated increase in MCAv was equivalent between menstrual cycle phases, and between female and male participants. Antisaccade reaction times reliably decreased from pre- to postexercise and frequentist and non-frequentist statistics demonstrated that the magnitude of the decrease was equivalent across FOL and LUT phases, and between female and male participants. Thus, results evince that menstrual cycle status should not serve as a basis limiting biologically female participants' inclusion in research examining exercise and EF.

Distinct cortical haemodynamics during squat-stand and continuous aerobic exercise do not influence the magnitude of a postexercise executive function benefit

A single bout of aerobic exercise benefits executive function (EF). A potential mechanism for this benefit is an exercise-mediated increase in cerebral blood flow (CBF) that elicits vascular endothelial shear-stress improving EF efficiency. Moderate intensity continuous aerobic exercise (MCE) asymptotically increases CBF, whereas continuous body weight squat-stand exercise (SSE) provides a large amplitude oscillatory response. Some work has proposed that an increase in CBF oscillation amplitude provides the optimal shear-stress for improving EF and brain health. We examined whether a large amplitude oscillatory CBF response associated with a single bout of SSE imparts a larger postexercise EF benefit than an MCE cycle ergometer protocol. Exercise changes in middle cerebral artery velocity (MCAv) were measured via transcranial Doppler ultrasound to estimate CBF, and pre- and postexercise EF was assessed via the antisaccade task. MCE produced a steady state increase in MCAv, whereas SSE produced a large amplitude MCAv oscillation. Both conditions produced a postexercise EF benefit that null hypothesis and equivalence tests showed to be comparable in magnitude. Accordingly, we provide a first demonstration that a single bout of SSE benefits EF; however, the condition's oscillatory CBF response does not impart a larger benefit than a time- and intensity-matched MCE protocol.

Acute stress imparts a transient benefit to task-switching that is not modulated following a single bout of exercise

Introduction

Cognitive flexibility represents a core component of executive function that promotes the ability to efficiently alternate-or "switch"-between different tasks. Literature suggests that acute stress negatively impacts cognitive flexibility, whereas a single bout of aerobic exercise supports a postexercise improvement in cognitive flexibility. Here, we examined whether a single bout of aerobic exercise attenuates a stress-induced decrement in task-switching.

Materials and Methods

Forty participants (age range = 19-30) completed the Trier Social Stress Test (TSST) and were randomized into separate Exercise or Rest groups entailing 20-min sessions of heavy intensity exercise (80% of heart rate maximum via cycle ergometer) or rest, respectively. Stress induction was confirmed via state anxiety and heart rate. Task-switching was assessed prior to the TSST (i.e., pre-TSST), following the TSST (i.e., post-TSST), and following Exercise and Rest interventions (i.e., post-intervention) via pro- (i.e., saccade to veridical target location) and antisaccades (i.e., saccade mirror-symmetrical to target location) arranged in an AABB task-switching paradigm. The underlying principle of the AABB paradigm suggests that when prosaccades are preceded by antisaccades (i.e., task-switch trials), the reaction times are longer compared to their task-repeat counterparts (i.e., unidirectional prosaccade switch-cost).

Results

As expected, the pre-TSST assessment yielded a prosaccade switch cost. Notably, post-TSST physiological measures indicated a reliable stress response and at this assessment a null prosaccade switch-cost was observed. In turn, post-intervention assessments revealed a switch-cost independent of Exercise and Rest groups.

Conclusion

Accordingly, the immediate effects of acute stress supported improved task-switching in young adults; however, these benefits were not modulated by a single bout of aerobic exercise.

A single bout of passive exercise mitigates a mental fatigue-induced inhibitory control deficit

Sustained cognitive effort associated with the psychomotor vigilance task (PVT) increases objective and subjective measures of mental fatigue and elicits a post-PVT inhibitory control deficit. In contrast, passive exercise wherein an individual's limbs are moved via an external force (i.e., mechanically driven cycle ergometer flywheel) provides a postexercise inhibitory control benefit linked to an exercise-based increase in cerebral blood flow. Here, we examined whether passive exercise performed concurrently with the PVT 'blunts' an inhibitory control deficit. On separate days, participants (N = 27) completed a 20 min PVT protocol (control condition) and same duration PVT protocol paired with passive cycle ergometry (passive exercise condition). Prior to (i.e., baseline), immediately after and 30 min after each condition inhibitory control was assessed via the antisaccade task. Antisaccades require a goal-directed eye movement (i.e., saccade) mirror-symmetrical to a target and provide an ideal tool for evaluating task-based changes in inhibitory control. PVT results showed that vigilance (as assessed via reaction time: RT) during control and passive exercise conditions decreased from the first to last 5 min of the protocol and increased subjective ratings of mental fatigue. As well, in the control condition, immediate (but not 30-min) post-intervention antisaccade RTs were longer than their baseline counterparts-a result evincing a transient mental fatigue-based inhibitory control deficit. For the passive exercise condition, immediate and 30-min post-intervention antisaccade RTs were shorter than their baseline counterparts and this result was linked to decreased subjective ratings of mental fatigue. Thus, passive exercise ameliorated the selective inhibitory control deficit associated with PVT-induced mental fatigue and thus provides a potential framework to reduce executive dysfunction in vigilance-demanding occupations.

Cerebral blood flow and immediate and sustained executive function benefits following single bouts of passive and active exercise

Passive exercise occurs when an individual's limbs are moved via an external force and is a modality that increases cerebral blood flow (CBF) and provides an immediate postexercise executive function (EF) benefit. To our knowledge, no work has examined for how long passive exercise benefits EF. Here, healthy young adults (N = 22; 7 female) used a cycle ergometer to complete three 20-min conditions: passive exercise (via mechanically driven flywheel), a traditional light intensity (37 W) "active" exercise condition (i.e., via volitional pedalling) and a non-exercise control condition. An estimate of CBF was obtained via transcranial Doppler ultrasound measurement of middle cerebral artery blood velocity (MCAv) and antisaccades (i.e., saccade mirror-symmetrical to a target) were completed prior to and immediately, 30- and 60-min following each condition to assess EF. Passive and active exercise increased MCAv; however, the increase was larger in the latter condition. In terms of antisaccades, passive and active exercise provided an immediate postexercise reaction time benefit. At the 30-min assessment, the benefit was observed for active but not passive exercise and neither produced a benefit at the 60-min assessment. Thus, passive exercise provided an evanescent EF "boost" and is a finding that may reflect a smaller cortical hemodynamic response.

Passive exercise increases cerebral blood flow velocity and supports a postexercise executive function benefit

Executive function entails high-level cognitive control supporting activities of daily living. Literature has shown that a single-bout of exercise involving volitional muscle activation (i.e., active exercise) improves executive function and that an increase in cerebral blood flow (CBF) may contribute to this benefit. It is, however, unknown whether non-volitional exercise (i.e., passive exercise) wherein an individual's limbs are moved via an external force elicits a similar executive function benefit. This is a salient question given that proprioceptive and feedforward drive from passive exercise increases CBF independent of the metabolic demands of active exercise. Here, in a procedural validation participants (n = 2) used a cycle ergometer to complete separate 20-min active and passive (via mechanically driven flywheel) exercise conditions and a non-exercise control condition. Electromyography showed that passive exercise did not increase agonist muscle activation or increase ventilation or gas exchange variables (i.e., V̇O₂ and V̇CO₂ ). In a main experiment participants (n = 28) completed the same exercise and control conditions and transcranial Doppler ultrasound showed that active and passive exercise (but not the control condition) increased CBF through the middle cerebral artery (ps <.001); albeit the magnitude was less during passive exercise. Notably, antisaccade reaction times prior to and immediately after each condition showed that active (p < .001) and passive (p = .034) exercise improved an oculomotor-based measure of executive function, whereas no benefit was observed in the control condition (p = .85). Accordingly, results evince that passive exercise 'boosts' an oculomotor-based measure of executive function and supports convergent evidence that increased CBF mediates this benefit.

The unidirectional prosaccade switch-cost: no evidence for the passive dissipation of an oculomotor task-set inertia

Cognitive flexibility is a core component of executive function and supports the ability to ‘switch’ between different tasks. Our group has examined the cost associated with switching between a prosaccade (i.e., a standard task requiring a saccade to veridical target location) and an antisaccade (i.e., a non-standard task requiring a saccade mirror-symmetrical to veridical target) in predictable (i.e., AABB) and unpredictable (e.g., AABAB…) switching paradigms. Results have shown that reaction times (RTs) for a prosaccade preceded by an antisaccade (i.e., task-switch trial) are longer than when preceded by its same task-type (i.e., task-repeat trial), whereas RTs for antisaccade task-switch and task-repeat trials do not differ. The asymmetrical switch-cost has been attributed to an antisaccade task-set inertia that proactively delays a subsequent prosaccade (i.e., the unidirectional prosaccade switch-cost). A salient question arising from previous work is whether the antisaccade task-set inertia passively dissipates or persistently influences prosaccade RTs. Accordingly, participants completed separate AABB (i.e., A = prosaccade, B = antisaccade) task-switching conditions wherein the preparation interval for each trial was ‘short’ (1000–2000 ms; i.e., the timeframe used in previous work), ‘medium’ (3000–4000 ms) and ‘long’ (5000–6000 ms). Results demonstrated a reliable prosaccade switch-cost for each condition (ps < 0.02) and two one-sided test statistics indicated that switch cost magnitudes were within an equivalence boundary (ps < 0.05). Hence, null and equivalence tests demonstrate that an antisaccade task-set inertia does not passively dissipate and represents a temporally persistent feature of oculomotor control.

Acute Effects of Different Exercise Intensities on Executive Function and Oculomotor Performance in Middle-Aged and Older Adults: Moderate-Intensity Continuous Exercise vs. High-Intensity Interval Exercise

A wealth of evidence has shown that a single bout of aerobic exercise can facilitate executive function. However, none of current studies on this topic have addressed whether the magnitude of the acute-exercise benefit on executive function and oculomotor performance is influenced by different aerobic exercise modes. The present study was thus aimed toward an investigation of the acute effects of high-intensity interval exercise (HIIE) vs. moderate-intensity continuous exercise (MICE) on executive-related oculomotor performance in healthy late middle-aged and older adults. Using a within-subject design, twenty-two participants completed a single bout of 30 min of HIIE, MICE, or a non-exercise-intervention (REST) session in a counterbalanced order. The behavioral [e.g., reaction times (RTs), coefficient of variation (CV) of the RT], and oculomotor (e.g., saccade amplitude, saccade latency, and saccadic peak velocity) indices were measured when participants performed antisaccade and prosaccade tasks prior to and after an intervention mode. The results showed that a 30-min single-bout of HIIE and MICE interventions shortened the RTs in the antisaccade task, with the null effect on the CV of the RT in the late middle-aged and older adults. In terms of oculomotor metrics, although the two exercise modes could not modify the performance in terms of saccade amplitudes and saccade latencies, the participants’ saccadic peak velocities while performing the oculomotor paradigm were significantly altered only following an acute HIIE intervention. The present findings suggested that a 30-min single-bout of HIIE and MICE interventions modulated post-exercise antisaccade control on behavioral performance (e.g., RTs). Nevertheless, the HIIE relative MICE mode appears to be a more effective aerobic exercise in terms of oculomotor control (e.g., saccadic peak velocities) in late middle-aged and older adults.

Cognitive ocular motor deficits and white matter damage chronically after sports-related concussion

A history of concussion has been linked to long-term cognitive deficits; however, the neural underpinnings of these abnormalities are poorly understood. This study recruited 26 asymptomatic male Australian footballers with a remote history of concussion (i.e. at least six months since last concussion), and 23 non-collision sport athlete controls with no history of concussion. Participants completed three ocular motor tasks (prosaccade, antisaccade and a cognitively complex switch task) to assess processing speed, inhibitory control and cognitive flexibility, respectively. Diffusion tensor imaging data were acquired using a 3 T MRI scanner, and analysed using tract-based spatial statistics, to investigate white matter abnormalities and how they relate to ocular motor performance. Australian footballers had significantly slower adjusted antisaccade latencies compared to controls (P = 0.035). A significant switch cost (i.e. switch trial error > repeat trial error) was also found on the switch task, with Australian footballers performing increased magnitude of errors on prosaccade switch trials relative to prosaccade repeat trials (P = 0.023). Diffusion tensor imaging analysis found decreased fractional anisotropy, a marker of white matter damage, in major white matter tracts (i.e. corpus callosum, corticospinal tract) in Australian footballers relative to controls. Notably, a larger prosaccade switch cost was significantly related to reduced fractional anisotropy in anterior white matter regions found to connect to the prefrontal cortex (i.e. a key cortical ocular motor centre involved in executive functioning and task switching). Taken together, Australian footballers with a history of concussion have ocular motor deficits indicative of poorer cognitive processing speed and cognitive flexibility, which are related to reduce white matter integrity in regions projecting to important cognitive ocular motor structures. These findings provide novel insights into the neural mechanisms that may underly chronic cognitive impairments in individuals with a history of concussion.

Exercise and Executive Function during Follicular and Luteal Menstrual Cycle Phases

PURPOSE

A single bout of aerobic or resistance exercise improves executive function. We sought to determine whether menstrual cycle variations in ovarian hormone concentrations differentially influence the expression and/or magnitude of a postexercise executive benefit.

METHODS

Eumenorrheic female participants completed 20-min single bouts of aerobic exercise (via cycle ergometer) at a moderate intensity (i.e., 80% of estimated lactate threshold) during the early follicular and midluteal phases of their menstrual cycle. Pre- and postexercise executive function was examined via antisaccades-an executive task requiring a saccade mirror-symmetrical to a visual stimulus. Antisaccades are an ideal tool for examining postexercise executive changes because the task is mediated via the same frontoparietal networks as modified following single-bout and chronic exercise.

RESULTS

Antisaccade reaction times decreased from the pre- to postexercise assessments by an average of 22 ms (P = 0.003), and this benefit was independent of changes in directional errors or end point accuracy (P's > 0.26). In other words, participants did not decrease their postexercise reaction times at the cost of increased planning times or execution errors. Most notably, the postexercise antisaccade benefit did not vary in magnitude across follicular or luteal phases (P = 0.33) and a two one-sided test statistic (i.e., equivalence testing) provided support for the null hypothesis (P = 0.008).

CONCLUSIONS

A postexercise executive benefit is independent of hormonal variations in the menstrual cycle. Further, our results evince that the phase of a female participant's menstrual cycle should not be a limiting factor in determining their inclusion in exercise neuroscience research.

Effects of blocked vs. interleaved administration mode on saccade preparatory set revealed using pupillometry

Eye movements have been used extensively to assess information processing and cognitive function. However, significant variability in saccade performance has been observed, which could arise from methodological variations across different studies. For example, prosaccades and antisaccades have been studied using either a blocked or interleaved design, which has a significant influence on error rates and latency. This is problematic as it makes it difficult to compare saccade performance across studies and may limit the ability to use saccades as a behavioural assay to assess neurocognitive function. Thus, the current study examined how administration mode influences saccade related preparatory activity by employing pupil size as a non-invasive proxy for neural activity related to saccade planning and execution. Saccade performance and pupil dynamics were examined in eleven participants as they completed pro- and antisaccades in blocked and interleaved paradigms. Results showed that administration mode significantly modulated saccade performance and preparatory activity. Reaction times were longer for both pro- and antisaccades in the interleaved condition, compared to the blocked condition (p < 0.05). Prosaccade pupil dilations were larger in the interleaved condition (p < 0.05), while antisaccade pupil dilations did not significantly differ between administration modes. Additionally, ROC analysis provided preliminary evidence that pupil size can effectively predict saccade directional errors prior to saccade onset. We propose that task-evoked pupil dilations reflect an increase in preparatory activity for prosaccades and the corresponding cognitive demands associated with interleaved administration mode. Overall, the results highlight the importance that administration mode plays in the design of neurocognitive tasks.

A single bout of moderate intensity exercise improves cognitive flexibility: evidence from task-switching

Executive function entails the core components of response  inhibition, working memory and cognitive flexibility. An accumulating literature has shown that a single bout of exercise improves the response inhibition  and working memory components of executive function; however, limited work has examined a putative exercise-related improvement to cognitive flexibility. To address this limitation, Experiment 1 entailed a 20-min session of moderate intensity aerobic exercise (via cycle ergometer), and pre- and post-exercise cognitive flexibility was examined via a task-switching paradigm involving alternating pro- and antisaccades (AABB: A = prosaccade, B = antisaccade). In Experiment 2, participants sat on the cycle ergometer without exercising (i.e., rest break) and the same AABB paradigm was examined pre- and post-break. We used an AABB pro- and antisaccade paradigm because previous work has shown that a prosaccade preceded by an antisaccade exhibits a reliable-and large magnitude-increase in reaction time, whereas the converse switch does not (i.e., the unidirectional prosaccade switch-cost). Experiment 1 showed a unidirectional prosaccade switch-cost pre-exercise (p = .012)-but not post-exercise (p = .30), and a two one-sided t test indicated that the latter comparison was within an equivalence boundary (p < .01). In contrast, Experiment 2 revealed a unidirectional prosaccade switch-cost at pre- and post-break assessments (ps < .01). Accordingly, our results indicate that a single bout of exercise improves cognitive flexibility and provides convergent evidence that exercise improves global components of executive function.

Increased cerebral blood flow supports a single-bout postexercise benefit to executive function: evidence from hypercapnia

A single bout of aerobic exercise improves executive function; however, the mechanism for the improvement remains unclear. One proposal asserts that an exercise-mediated increase in cerebral blood flow (CBF) enhances the efficiency of executive-related cortical structures. To examine this, participants completed separate 10-min sessions of moderate- to heavy-intensity aerobic exercise, a hypercapnic environment (i.e., 5% CO₂), and a nonexercise and nonhypercapnic control condition. The hypercapnic condition was included because it produces an increase in CBF independent of metabolic demands. An estimate of CBF was achieved via transcranial Doppler ultrasound and near-infrared spectroscopy that provided measures of middle cerebral artery blood velocity (BV) and deoxygenated hemoglobin (HHb), respectively. Exercise intensity was adjusted to match participant-specific changes in BV and HHb associated with the hypercapnic condition. Executive function was assessed before and after each session via antisaccades (i.e., saccade mirror-symmetrical to a target) because the task is mediated via the same executive networks that demonstrate task-dependent modulation following single and chronic bouts of aerobic exercise. Results showed that hypercapnic and exercise conditions were associated with comparable BV and HHb changes, whereas the control condition did not produce a change in either metric. In terms of antisaccade performance, the exercise and hypercapnic, but not control, conditions demonstrated improved postcondition reaction times (RT), and the magnitude of the hypercapnic and exercise-based increase in estimated CBF was reliably related to the postcondition improvement in RT. Accordingly, results evince that an increase in CBF represents a candidate mechanism for a postexercise improvement in executive function.NEW & NOTEWORTHY Single-bout aerobic exercise "boosts" executive function, and increased cerebral blood flow (CBF) has been proposed as a mechanism for the benefit. In this study, participants completed 10 min of aerobic exercise and 10 min of inhaling a hypercapnic gas, a manipulation known to increase CBF independently of metabolic demands. Both exercise and hypercapnic conditions improved executive function for at least 20 min. Accordingly, an increase in CBF is a candidate mechanism for the postexercise improvement in executive function.

Ocular motor measures of visual processing changes in visual snow syndrome

OBJECTIVE

To determine whether changes to cortical processing of visual information can be evaluated objectively using 3 simple ocular motor tasks to measure performance in patients with visual snow syndrome (VSS).

METHODS

Sixty-four patients with VSS (32 with migraine and 32 with no migraine) and 23 controls participated. Three ocular motor tasks were included: prosaccade (PS), antisaccade (AS), and interleaved AS-PS tasks. All these tasks have been used extensively in both neurologically healthy and diseased states.

RESULTS

We demonstrated that, compared to controls, the VSS group generated significantly shortened PS latencies (p = 0.029) and an increased rate of AS errors (p = 0.001), irrespective of the demands placed on visual processing (i.e., task context). Switch costs, a feature of the AS-PS task, were comparable across groups, and a significant correlation was found between shortened PS latencies and increased AS error rates for patients with VSS (r = 0.404).

CONCLUSION

We identified objective and quantifiable measures of visual processing changes in patients with VSS. The absence of any additional switch cost on the AS-PS task in VSS suggests that the PS latency and AS error differences are attributable to a speeded PS response rather than to impaired executive processes more commonly implicated in poorer AS performance. We propose that this combination of latency and error deficits, in conjunction with intact switching performance, will provide a VS behavioral signature that contributes to our understanding of VSS and may assist in determining the efficacy of therapeutic interventions.

Executive Dysfunction after a Sport-Related Concussion Is Independent of Task-Based Symptom Burden

A sport-related concussion (SRC) results in short- and long-term deficits in oculomotor control; however, it is unclear whether this change reflects executive dysfunction and/or a performance decrement caused by an increase in task-based symptom burden. Here, individuals with a SRC - and age- and sex-matched controls - completed an antisaccade task (i.e., saccade mirror-symmetrical to a target) during the early (initial assessment ≤12 days) and later (follow-up assessment <30 days) stages of recovery. Antisaccades were used because they require top-down executive control and exhibit performance decrements following an SRC. Reaction time (RT) and directional errors were included with pupillometry, because pupil size in the antisaccade task has been shown to provide a neural proxy for executive control. In addition, the Sport-Concussion Assessment Tool (SCAT-5) symptom checklist was completed prior to and after each oculomotor assessment to identify a possible task-based increase in symptomology. The SRC group yielded longer initial assessment RTs, more directional errors, and larger task-evoked pupil dilations (TEPD) than the control group. At the follow-up assessment, RTs for the SRC and control group did not reliably differ; however, the former demonstrated more directional errors and larger TEPDs. SCAT-5 symptom severity scores did not vary from the pre- to post-oculomotor evaluation for either initial or follow-up assessments. Accordingly, an SRC imparts a persistent executive dysfunction to oculomotor planning independent of a task-based increase in symptom burden. These findings evince that antisaccades serve as an effective tool to identify subtle executive deficits during the early and later stages of SRC recovery.

Pro- and antisaccade task-switching: response suppression-and not vector inversion-contributes to a task-set inertia

Alternating between different tasks represents an executive function essential to activities of daily living. In the oculomotor literature, reaction times (RT) for a 'standard' and stimulus-driven (SD) prosaccade (i.e., saccade to target at target onset) are increased when preceded by a 'non-standard' antisaccade (i.e., saccade mirror-symmetrical to target at target onset), whereas the converse switch does not elicit an RT cost. The prosaccade switch-cost has been attributed to lingering neural activity-or task-set inertia-related to the antisaccade executive demands of response suppression and vector inversion. It is, however, unclear whether response suppression and/or vector inversion contribute to the prosaccade switch-cost. Experiment 1 of the present work had participants alternate (i.e., AABB paradigm) between minimally delayed (MD) pro- and antisaccades. MD saccades require a response after target extinction and necessitate response suppression for both pro- and antisaccades-a paradigm providing a framework to determine whether vector inversion contributes to a task-set inertia. In Experiment 2, participants alternated between SD pro- and MD antisaccades-a paradigm designed to determine if a switch-cost is selectively imparted when a SD and standard response is preceded by a non-standard response. Experiment 1 showed that RTs for MD pro- and antisaccades were refractory to the preceding trial-type; that is, vector inversion did not engender a switch-cost. Experiment 2 indicated that RTs for SD prosaccades were increased when preceded by an MD antisaccade. Accordingly, response suppression engenders a task-set inertia but only for a subsequent stimulus-driven and standard response (i.e., SD prosaccade). Such a result is in line with the view that response suppression is a hallmark feature of executive function.

Oculomotor Executive Dysfunction during the Early and Later Stages of Sport-Related Concussion Recovery

Executive dysfunction represents the most persistent sequela of mild traumatic brain injury. It is, however, largely unclear whether a sport-related concussion similarly contributes to a persistent executive dysfunction even when an athlete has been cleared medically for return to play. Here, individuals with a diagnosis of a sport-related concussion-and their age- and sex-matched controls-completed an oculomotor assessment during the acute and later stages of injury recovery. Prosaccades (i.e., saccade to a target) and executive-related antisaccades (i.e., saccade mirror-symmetrical to a target) were completed: (1) 2-6 days after a concussive event (initial assessment), and (2) 14-20 days after the initial oculomotor assessment when individuals were cleared for return to play (follow-up assessment). At the initial assessment, the concussed group produced antisaccade reaction times (RT) that were 93 ms longer than the control group (p < 0.001), whereas prosaccade RTs did not differ between groups (p = 0.25). At the follow-up assessment, concussed and control groups produced comparable pro- and antisaccade RTs (ps >0.31); however, the former group exhibited a continued increase in directional errors (p < 0.05). That initial assessment antisaccades-but not prosaccades-differed between groups indicates that the acute recovery of a concussion is associated with a selective executive-related oculomotor deficit, and the continued increase in directional errors at the follow-up assessment suggests that such a deficit persists even when an athlete has been cleared medically for return to play. The antisaccade task may therefore serve to assess subtle executive deficits and determine when an athlete may return to play safely.

Switch costs in inhibitory control and voluntary behaviour: A computational study of the antisaccade task

An integral aspect of human cognition is the ability to inhibit stimulus-driven, habitual responses, in favour of complex, voluntary actions. In addition, humans can also alternate between different tasks. This comes at the cost of degraded performance when compared to repeating the same task, a phenomenon called the "task-switch cost." While task switching and inhibitory control have been studied extensively, the interaction between them has received relatively little attention. Here, we used the SERIA model, a computational model of antisaccade behaviour, to draw a bridge between them. We investigated task switching in two versions of the mixed antisaccade task, in which participants are cued to saccade either in the same or in the opposite direction to a peripheral stimulus. SERIA revealed that stopping a habitual action leads to increased inhibitory control that persists onto the next trial, independently of the upcoming trial type. Moreover, switching between tasks induces slower and less accurate voluntary responses compared to repeat trials. However, this only occurs when participants lack the time to prepare the correct response. Altogether, SERIA demonstrates that there is a reconfiguration cost associated with switching between voluntary actions. In addition, the enhanced inhibition that follows antisaccade but not prosaccade trials explains asymmetric switch costs. In conclusion, SERIA offers a novel model of task switching that unifies previous theoretical accounts by distinguishing between inhibitory control and voluntary action generation and could help explain similar phenomena in paradigms beyond the antisaccade task.

Older adults elicit a single-bout post-exercise executive benefit across a continuum of aerobically supported metabolic intensities

Ten minutes of aerobic or resistance training can 'boost' executive function in older adults. Here, we examined whether the magnitude of the exercise benefit is influenced by exercise intensity. Older adults (N = 17: mean age = 73 years) completed a volitional test to exhaustion (VO_2peak) via treadmill to determine participant-specific moderate (80% of lactate threshold (LT)), heavy (15% of the difference between LT and VO_2peak) and very-heavy (50% of the difference between LT and VO_2peak) exercise intensities. Subsequently, in separate sessions all participants completed 10-min constant load single-bouts of exercise at each intensity. Pre- and post-exercise executive function were examined via the antisaccade task. Antisaccades require a saccade mirror-symmetrical to a target and extensive evidence has shown that antisaccades are supported via frontoparietal networks that demonstrate task-dependent changes following single-bout and chronic exercise. We also included a non-executive task (saccade to veridical target location; i.e., prosaccade) to determine whether a putative post-exercise benefit is specific to executive-related oculomotor control. Results showed that VO₂ and psychological ratings of perceived exertion concurrently increased with increasing exercise intensity. As well, antisaccade reaction times showed a 24 ms (i.e., 8%) reduction from pre- to post-exercise assessments (p < .001), whereas prosaccade values did not (p = .19). Most notably, the post-exercise change in antisaccade RTs did not reliably vary with exercise intensity. Further, for each exercise intensity participants' cardiorespiratory fitness level was unrelated to the magnitude of the post-exercise executive benefit (ps > .13). Accordingly, an exercise duration as brief as 10-min provides a selective benefit to executive function in older adults across the continuum of moderate to very-heavy intensities.

Multiple sclerosis: Executive dysfunction, task switching and the role of attention

Background

It has been suggested that switching ability might not be affected in multiple sclerosis (MS) as previously thought; however, whether this is true under more ‘real-world’ conditions when asymmetry in task difficulty is present has not been ascertained.

Objective

The objective of this paper is to examine the impact of task difficulty asymmetry on task switching ability in MS.

Method

An ocular motor (OM) paradigm that interleaves the simple task of looking towards a target (prosaccade, PS) with the cognitively more difficult task of looking away from a target (antisaccade, PS) was used. Two switching conditions: (1) PS switch cost, switching to a simple task from a difficult task (PS switch), relative to performing two simple tasks concurrently (PS repeat); (2) AS switch cost, switching to a difficult task from a simple task (AS switch) relative to performing two difficult tasks concurrently (AS repeat). Forty-five relapsing–remitting MS patients and 30 control individuals were compared.

Results

Controls and patients produced a similar magnitude PS switch cost, suggesting that task difficulty asymmetry does not detrimentally impact MS patients when transitioning from a more difficult task to a simpler task. However, MS patients alone found switching from the simpler PS trial to the more difficult AS trial easier (shorter latency and reduced error) than performing two AS trials consecutively (AS switch benefit). Further, MS patients performed significantly more errors than controls when required to repeat the same trial consecutively.

Conclusion

MS patients appear to find the maintenance of task-relevant processes difficult not switching per se, with deficits exacerbated under increased attentional demands.

A 24-Week Multi-Modality Exercise Program Improves Executive Control in Older Adults with a Self-Reported Cognitive Complaint: Evidence from the Antisaccade Task

Exercise programs involving aerobic and resistance training (i.e., multiple-modality) have shown promise in improving cognition and executive control in older adults at risk, or experiencing, cognitive decline. It is, however, unclear whether cognitive training within a multiple-modality program elicits an additive benefit to executive/cognitive processes. This is an important question to resolve in order to identify optimal training programs that delay, or ameliorate, executive deficits in persons at risk for further cognitive decline. In the present study, individuals with a self-reported cognitive complaint (SCC) participated in a 24-week multiple-modality (i.e., the M2 group) exercise intervention program. In addition, a separate group of individuals with a SCC completed the same aerobic and resistance training as the M2 group but also completed a cognitive-based stepping task (i.e., multiple-modality, mind-motor intervention: M4 group). Notably, pre- and post-intervention executive control was examined via the antisaccade task (i.e., eye movement mirror-symmetrical to a target). Antisaccades are an ideal tool for the study of individuals with subtle executive deficits because of its hands- and language-free nature and because the task's neural mechanisms are linked to neuropathology in cognitive decline (i.e., prefrontal cortex). Results showed that M2 and M4 group antisaccade reaction times reliably decreased from pre- to post-intervention and the magnitude of the decrease was consistent across groups. Thus, multi-modality exercise training improved executive performance in persons with a SCC independent of mind-motor training. Accordingly, we propose that multiple-modality training provides a sufficient intervention to improve executive control in persons with a SCC.

Executive-related oculomotor control is improved following a 10-min single-bout of aerobic exercise: Evidence from the antisaccade task

Previous work has shown that a single-bout of moderate-to-vigorous intensity exercise improves task-specific activity within frontoparietal networks and produces a short-term 'boost' to executive-related cognitive control - an effect in healthy young adults that is reported to be selective to exercise durations of 20min or greater. The present study sought to determine whether such a 'boost' extends to an exercise duration as brief as 10min. Healthy young adults performed a 10-min single-bout of moderate-to-vigorous intensity aerobic exercise (i.e., via a cycle ergometer) and pre- and post-exercise executive control was examined via the antisaccade task. Antisaccades are an executive task requiring a goal-directed eye movement (i.e., a saccade) mirror-symmetrical to a visual stimulus. The hands- and language-free nature of antisaccades coupled with the temporal precision of eye-tracking technology make it an ideal tool for identifying executive performance changes. Moreover, an extensive literature has shown that antisaccades are mediated via frontoparietal networks that are modulated following single-bout and chronic exercise training. Results showed that antisaccade reaction time (RT) reliably decreased by 27ms from pre- to post-exercise assessments. Further, the percentage of antisaccade directional errors did not reliably vary from the pre- (13%) to post-exercise (9%) assessments - a result indicating that the RT improvement was unrelated to a speed-accuracy trade-off. A follow-up experiment involving antisaccade sessions separated by a non-exercise interval did not show a similar RT modulation. Thus, a 10-min bout of moderate-to-vigorous intensity aerobic exercise benefits executive-related oculomotor control, and is a finding we attribute to an exercise-based increase in attention/arousal and/or improved task-specific activity within the frontoparietal networks supporting antisaccades.

Brain structure and intragenic DNA methylation are correlated, and predict executive dysfunction in fragile X premutation females

DNA methylation of the Fragile X mental retardation 1 (FMR1) exon 1/intron 1 boundary has been associated with executive dysfunction in female carriers of a FMR1 premutation (PM: 55-199 CGG repeats), whereas neuroanatomical changes have been associated with executive dysfunction in PM males. To our knowledge, this study for the first time examined the inter-relationships between executive function, neuroanatomical structure and molecular measures (DNA methylation and FMR1 mRNA levels in blood) in PM and control (<44 CGG repeats) females. In the PM group, FMR1 intron 1 methylation was positively associated with executive function and cortical thickness in middle and superior frontal gyri, and left inferior parietal gyrus. By contrast, in the control group, FMR1 intron 1 methylation was negatively associated with cortical thickness of the left middle frontal gyrus and superior frontal gyri. No significant associations were revealed for either group between FMR1 mRNA and neuroanatomical structure or executive function. In the PM group, the lack of any significant association between FMR1 mRNA levels and phenotypic measures found in this study suggests that either FMR1 expression is not well conserved between tissues, or that FMR1 intron 1 methylation is linked to neuroanatomical and cognitive phenotype in PM females via a different mechanism.

Disassociation between brain activation and executive function in fragile X premutation females

Executive dysfunction has been demonstrated among premutation (PM) carriers (55-199 CGG repeats) of the Fragile X mental retardation 1 (FMR1) gene. Further, alterations to neural activation patterns have been reported during memory and comparison based functional magnetic resonance imaging (fMRI) tasks in these carriers. For the first time, the relationships between fMRI neural activation during an interleaved ocular motor prosaccade/antisaccade paradigm, and concurrent task performance (saccade measures of latency, accuracy and error rate) in PM females were examined. Although no differences were found in whole brain activation patterns, regions of interest (ROI) analyses revealed reduced activation in the right ventrolateral prefrontal cortex (VLPFC) during antisaccade trials for PM females. Further, a series of divergent and group specific relationships were found between ROI activation and saccade measures. Specifically, for control females, activation within the right VLPFC and supramarginal gyrus correlated negatively with antisaccade latencies, while for PM females, activation within these regions was found to negatively correlate with antisaccade accuracy and error rate (right VLPFC only). For control females, activation within frontal and supplementary eye fields and bilateral intraparietal sulci correlated with prosaccade latency and accuracy; however, no significant prosaccade correlations were found for PM females. This exploratory study extends previous reports of altered prefrontal neural engagement in PM carriers, and clearly demonstrates dissociation between control and PM females in the transformation of neural activation into overt measures of executive dysfunction. Hum Brain Mapp 38:1056-1067, 2017. © 2016 Wiley Periodicals, Inc.

Freezing of gait is associated with increased saccade latency and variability in Parkinson's disease

OBJECTIVE

Freezing of gait (FOG) is a locomotor disturbance in Parkinson disease (PD) related to impaired motor automaticity. In this study, we investigated the impact of freezing on automaticity in the oculomotor system using an anti-saccade paradigm.

METHODS

Subjects with PD with (PD-FOG, n=13) and without (PD-NON, n=13) FOG, and healthy age-matched controls (CTRL, n=12) completed automatic pro-saccades and non-automatic anti-saccades. Primary outcomes were saccade latency, velocity, and gain.

RESULTS

PD-FOG (pro-saccade latency=271ms, anti-saccade latency=412ms) were slower to execute both types of saccades compared to PD-NON (253ms, 330ms) and CTRL (246ms, 327ms). Saccade velocity and gain variability was also increased in PD-FOG.

CONCLUSIONS

Saccade performance was affected in PD-FOG for both types of saccades, indicating differences in automaticity and control in the oculomotor system related to freezing.

SIGNIFICANCE

These results and others show that FOG impacts non-gait motor functions, suggesting global motor impairment in PD-FOG.

Alternating between pro- and antisaccades: switch-costs manifest via decoupling the spatial relations between stimulus and response

Antisaccades are a nonstandard task requiring a response mirror-symmetrical to the location of a target. The completion of an antisaccade has been shown to delay the reaction time (RT) of a subsequent prosaccade, whereas the converse switch elicits a null RT cost (i.e., the unidirectional prosaccade switch-cost). The present study sought to determine whether the prosaccade switch-cost arises from low-level interference specific to the sensory features of a target (i.e., modality-dependent) or manifests via the high-level demands of dissociating the spatial relations between stimulus and response (i.e., modality-independent). Participants alternated between pro- and antisaccades wherein the target associated with the response alternated between visual and auditory modalities. Thus, the present design involved task-switch (i.e., switching from a pro- to antisaccade and vice versa) and modality-switch (i.e., switching from a visual to auditory target and vice versa) trials as well as their task- and modality-repetition counterparts. RTs were longer for modality-switch than modality-repetition trials. Notably, however, modality-switch trials did not nullify or lessen the unidirectional prosaccade switch-cost; that is, the magnitude of the RT cost for task-switch prosaccades was equivalent across modality-switch and modality-repetition trials. Thus, competitive interference within a sensory modality does not contribute to the unidirectional prosaccade switch-cost. Instead, the modality-independent findings evince that dissociating the spatial relations between stimulus and response instantiates a high-level and inertially persistent nonstandard task-set that impedes the planning of a subsequent prosaccade.

The antisaccade task: visual distractors elicit a location-independent planning 'cost'

The presentation of a remote – but not proximal – distractor concurrent with target onset increases prosaccade reaction times (RT) (i.e., the remote distractor effect: RDE). The competitive integration model asserts that the RDE represents the time required to resolve the conflict for a common saccade threshold between target- and distractor-related saccade generating commands in the superior colliculus. To our knowledge however, no previous research has examined whether remote and proximal distractors differentially influence antisaccade RTs. This represents a notable question because antisaccades require decoupling of the spatial relations between stimulus and response (SR) and therefore provide a basis for determining whether the sensory- and/or motor-related features of a distractor influence response planning. Participants completed pro- and antisaccades in a target-only condition and conditions wherein the target was concurrently presented with a proximal or remote distractor. As expected, prosaccade RTs elicited a reliable RDE. In contrast, antisaccade RTs were increased independent of the distractor’s spatial location and the magnitude of the effect was comparable across each distractor location. Thus, distractor-related antisaccade RT costs are not accounted for by a competitive integration between conflicting saccade generating commands. Instead, we propose that a visual distractor increases uncertainty related to the evocation of the response-selection rule necessary for decoupling SR relations.

Task-switching effects for visual and auditory pro- and antisaccades: evidence for a task-set inertia

The completion of an antisaccade delays the reaction time (RT) of a subsequent prosaccade; however, the converse switch does not influence RT. In accounting for this result, the task-set inertia hypothesis contends that antisaccades engender a persistent nonstandard task-set that delays the planning of a subsequent prosaccade. In contrast, the coordinate system transformation hypothesis asserts that the transformation required to construct a mirror-symmetrical target representation persistently inhibits prosaccade planning. The authors tested the latter hypothesis by examining switch-costs for pro- and antisaccades directed to visual (i.e., the stimuli used in previous work) and auditory targets. Notably, auditory cues are specified in a head-centered frame of reference prior to their conversion into the retinocentric coordinates necessary for saccade output. Thus, if the coordinate system transformation hypothesis is correct then auditory pro- and antisaccades should elicit a bidirectional switch-cost because each requires a coordinate transformation. RTs for visual and auditory modalities showed a reliable--and equivalent magnitude--prosaccade switch-cost. Moreover, performance (e.g., movement time) and kinematic (e.g., velocity) variables indicated the switch-cost was restricted to response planning. As such, results are incompatible with the coordinate system transformation hypothesis and therefore provide convergent evidence that a task-set inertia contributes to the prosaccade switch-cost.

Oculomotor task switching: alternating from a nonstandard to a standard response yields the unidirectional prosaccade switch-cost

The completion of an antisaccade (i.e., a nonstandard task) lengthens the reaction time (RT) of a subsequent prosaccade: a behavioral phenomenon termed the unidirectional prosaccade switch-cost. One explanation for the unidirectional prosaccade switch-cost is suppressing a stimulus-driven prosaccade during the preceding antisaccade trial engenders a residual inhibition of the oculomotor networks that support prosaccade planning (i.e., the oculomotor inhibition hypothesis). Alternatively, the unidirectional prosaccade switch-cost may reflect the persistent activation of the antisaccade's nonstandard task rules (i.e., task set), which delays the planning of the next prosaccade (i.e., task-set inertia hypothesis). To determine which hypothesis provides the most parsimonious account for the unidirectional prosaccade switch-cost, participants alternated between pro- and antisaccades wherein task instructions (i.e., pro- and antisaccade) were provided before (i.e., classic cuing) or concurrent (i.e., delayed cuing) with response cuing. Importantly, pro- and antisaccades elicited via the delayed cuing condition required the suppression of a stimulus-driven prosaccade at response cuing (i.e., response suppression) to discern the appropriate to-be-performed task. Results showed that classic and delayed antisaccades, but not delayed prosaccades, lengthened the RT of subsequent prosaccades. That delayed prosaccades, which require response suppression for their successful execution, did not lengthen the RT of subsequent prosaccades indicates that the oculomotor inhibition hypothesis does not account for the unidirectional prosaccade switch-cost. Instead, the current findings are in line with the assertion that the task set associated with a nonstandard antisaccade persists inertially and delays the planning of a subsequent prosaccade (i.e., task-set inertia hypothesis).