Repeat Trials Research Articles

453 Cost-Effectiveness of Requalifying for Positive Airway Pressure Treatment After Initial Nonadherence

Abstract Introduction Obstructive sleep apnea (OSA) is effectively treated with continuous positive airway pressure (CPAP). However, many people are not able to become adherent in the initial 90-day trial window for this therapy. Medicare requires a polysomnography and repeat trial documenting adherence before continuing payment for these services. Oral appliance therapy (OAT) is also an OSA first-line therapy but is less effective than CPAP. Methods We created a decision tree to model 4 strategies over a 5-year time horizon: (1) current policy, (2) direct referral for CPAP equipment, (3) OAT followed by CPAP under current policy, and (4) OAT followed by direct CPAP referral in a the Medicare population with mild-moderate OSA and nonadherence to a first attempt at CPAP therapy. Medicare fee schedules in 2020 defined costs. Incremental cost-effectiveness (ICER) was used to identify the supreme strategy Results The current policy was the most expensive. Both the current policy and direct DME referral were dominated by starting with OAT. OAT followed by titration was the most cost-effective strategy with an ICER of $42,586.47. The ICER was sensitive to adherence in the direct CPAP strategy and probability of getting CPAP equipment (vs. lost to follow-up). Conclusion Starting with OAT therapy in those that were CPAP nonadherent on first attempt is cost-effective. Despite decreased effectiveness, the increase adherence to OAT make it an attractive option for retrial of OSA therapy. If OAT therapy fails, the current policy is more cost-effective than direct CPAP referral. Support (if any) This study was supported Career Development Award IK2CX001882 from the United States (U.S.) Department of Veterans Affairs Clinical Sciences Research and Development Service. The contents of this work do not represent the views of the Department of Veterans Affairs or the United States government.

Shifting attention between modalities: Revisiting the modality-shift effect in autism

Selective attention to a sensory modality has been observed experimentally in studies of the modality-shift effect – a relative performance benefit for targets preceded by a target in the same modality, compared to a different modality. Differences in selective attention are commonly observed in autism and we investigated whether exogenous (automatic) shift costs between modalities are increased. Autistic adults and neurotypical controls made speeded discrimination responses to simple visual, tactile and auditory targets. Shift costs were observed for each target modality in participant response times and were largest for auditory targets, reflective of fast responses on auditory repeat trials. Critically, shift costs were similar between the groups. However, integrating speed and accuracy data using drift-diffusion modelling revealed that shift costs in drift rates (reflecting the quality of information extracted from the stimulus) were reduced for autistic participants compared with neurotypicals. It may be that, unlike neurotypicals, there is little difference between attention within and between sensory modalities for autistic people. This finding also highlights the benefit of combining reaction time and accuracy data using decision models to better characterise selective attention in autism.

The Wisconsin Card Sorting Test: Split-Half Reliability Estimates for a Self-Administered Computerized Variant

Self-administered computerized assessment has the potential to increase the reach of neuropsychological assessment. The present study reports the first split-half reliability estimates for a self-administered computerized variant of the Wisconsin Card Sorting Test (WCST), which is considered as a gold standard for the neuropsychological assessment of executive functions. We analyzed data from a large sample of young volunteers (N = 375). Split-half reliability estimates for perseveration errors, set-loss errors, and inference errors were all above 0.90. Split-half reliability estimates for response time measures on switch and repeat trials exceeded 0.95. Our results indicated sufficient split-half reliability for a self-administered computerized WCST, paving the way for an advanced digital assessment of executive functions. We discuss potential effects of test formats, administration variants, and sample characteristics on split-half reliability.

Statistical uncertainty in bench-scale flammability tests

Standardized testing procedures and experimental studies in fire safety science specify repeat trials in an effort to minimize the impact of statistical variation on the presented results. Bench-scale flammability testing procedures typically require a constant number of trials – generally a total of three – across all experimental conditions. A series of experiments was conducted to quantify the influence of trial quantity on the statistical variation in Cone Calorimeter results; sets of 100 identical trials were conducted using black PMMA for three different heat flux exposures (20, 40, and 60 kW/m2). Gaussian statistics were applied to the time to ignition data and time-resolved mass loss rate data to illustrate the influence of trial quantity on predicted statistical uncertainty. Statistical variation observed for time to ignition data was found to decrease with increasing heat flux while the variation observed in the MLR data increased with increasing heat flux. The statistical uncertainty was found to decrease as a function of 1/n for n trials. The presented statistical analysis requires population characteristics to be known, or assumed, a priori; the results, however, demonstrate the importance of considering statistical uncertainty in addition to the variation within data collected under different exposure conditions.

Structuralist mental representation of dual-action demands: Evidence for compositional coding from dual tasks with low cross-task dimensional overlap

The present study asks how behavioral (dual-action) demands in dual tasks are mentally represented and whether changes in representation might govern practice-related dual-task performance improvements. Three different representation accounts were empirically tested based on the idea that dual-action demands required in a dual-task trial might be represented in different ways. According to a compositional (Structuralist) account, component tasks remain structurally intact when combined with another task. In contrast, a holistic (Gestalt) account posits that dual-action requirements in dual tasks are represented holistically and entirely distinct from its component action requirements. Finally, a contextual change account assumes that a change in context (e.g., from single- to dual-action requirement) generally impedes response retrieval, similar to repeating a response while the task context switches. To address this issue, we analyzed trial-by-trial effects in a single/dual switch paradigm (SDS paradigm, involving a randomized mix of single- and dual-task trials within blocks). Specifically, we analyzed performance in an extensive dual-task training setting (involving training sessions across several days) combining an auditory-vocal task and a visual-manual task. The results indicated that, throughout practice, nearly all relevant comparisons of performance between complete switch trials (e.g., between the two single tasks) and partial repetition trials (e.g., from dual to single task) revealed partial repetition benefits, that is, for both the auditory-vocal and the visual-manual task, and for both single- and dual-task performance analyses. Therefore, dual-action requirements in the present dual-task setting are mentally represented in a compositional, Structuralist fashion, probably due to low between-task dimensional overlap.

Mechanotendography: description and evaluation of a novel method for investigating the physiological mechanical oscillations of tendons using a piezo-based measurement system.

The mechanotendography (MTG) is a method for analyzing the mechanical oscillations of tendons during muscular actions. The aim of this investigation was to evaluate the technical reliability of a piezo-based measurement system used for MTG. The reliability measurements were performed by using audio samples played by a subwoofer. The thereby generated pressure waves were recorded by a piezo-based measurement system. An audio of 40 Hz sine oscillations and four different formerly in vivo recorded MTG-signals were converted into audio files and were used as test signals. Five trials with each audio were performed and one audio was used for repetition trials on another day. The signals’ correlation was estimated by Spearman (MCC) and intraclass correlation coefficients (ICC(3,1)), Cronbach’s alpha (CA) and by mean distances (MD). All parameters were compared between repetition and randomized matched signals. The repetition trials show high correlations (MCC: 0.86 ± 0.13, ICC: 0.89 ± 0.12, CA: 0.98 ± 0.03), low MD (0.03 ± 0.03V) and differ significantly from the randomized matched signals (MCC: 0.15 ± 0.10, ICC: 0.17 ± 0.09, CA: 0.37 ± 0.16, MD: 0.19 ± 0.01V) (p = 0.001 – 0.043). This speaks for an excellent reliability of the measurement system. Presuming the skin above superficial tendons oscillates adequately, we estimate this tool as valid for the application in musculoskeletal system.

Mechanotendography: description and evaluation of a novel method for investigating the physiological mechanical oscillations of tendons using a piezo-based measurement system

The mechanotendography (MTG) is a method for analyzing the mechanical oscillations of tendons during muscular actions. The aim of this investigation was to evaluate the technical reliability of a piezo-based measurement system used for MTG. The reliability measurements were performed by using audio samples played by a subwoofer. The thereby generated pressure waves were recorded by a piezo-based measurement system. An audio of 40 Hz sine oscillations and four different formerly in vivo recorded MTG-signals were converted into audio files and were used as test signals. Five trials with each audio were performed and one audio was used for repetition trials on another day. The signals’ correlation was estimated by Spearman (MCC) and intraclass correlation coefficients (ICC(3,1)), Cronbach’s alpha (CA) and by mean distances (MD). All parameters were compared between repetition and randomized matched signals. The repetition trials show high correlations (MCC: 0.86 ± 0.13, ICC: 0.89 ± 0.12, CA: 0.98 ± 0.03), low MD (0.03 ± 0.03V) and differ significantly from the randomized matched signals (MCC: 0.15 ± 0.10, ICC: 0.17 ± 0.09, CA: 0.37 ± 0.16, MD: 0.19 ± 0.01V) (p = 0.001 – 0.043). This speaks for an excellent reliability of the measurement system. Presuming the skin above superficial tendons oscillates adequately, we estimate this tool as valid for the application in musculoskeletal system.

Predicting obstetrical anal sphincter injuries in patients who undergo vaginal birth after cesarean delivery

Women with a history of previous cesarean delivery must weigh the numerous potential risks and benefits of elective repeat cesarean delivery or trial of labor after cesarean delivery. Notably, 1 important risk of vaginal delivery is obstetrical anal sphincter injuries. Furthermore, the rate of obstetrical anal sphincter injuries is high among women undergoing vaginal birth after cesarean delivery. However, the risk of obstetrical anal sphincter injuries is not routinely included in the trial of labor after cesarean delivery counseling, and there is no tool available to risk stratify obstetrical anal sphincter injuries among women undergoing vaginal birth after cesarean delivery. This study aimed to develop and validate a predictive model to estimate the risk of obstetrical anal sphincter injuries in the setting of vaginal birth after cesarean delivery population to improve antenatal counseling of patients regarding risks of trial of labor after cesarean delivery. This study was a secondary subgroup analysis of the Maternal-Fetal Medicine Units Network Trial of Labor After Cesarean Delivery prospective cohort (1999-2002). We identified women within the Maternal-Fetal Medicine Units Network cohort with 1 previous cesarean delivery followed by a term vaginal birth after cesarean delivery. This Maternal-Fetal Medicine Units Network Vaginal Birth After Cesarean Delivery cohort was stratified into 2 groups based on the presence of obstetrical anal sphincter injuries, and baseline characteristics were compared with bivariate analysis. Significant covariates in bivariate testing were included in a backward stepwise logistic regression model to identify independent risk factors for obstetrical anal sphincter injuries and generate a predictive model for obstetrical anal sphincter injuries in the setting of vaginal birth after cesarean delivery. Internal validation was performed using bootstrapped bias-corrected estimates of model concordance indices, Brier scores, Hosmer-Lemeshow chi-squared values, and calibration plots. External validation was performed using data from a single-site retrospective cohort of women with a singleton vaginal birth after cesarean delivery from January 2011 to December2016. In this study, 10,697 women in the Maternal-Fetal Medicine Units Network Trial of Labor After Cesarean Delivery cohort met the inclusion criteria, and 669 women (6.3%) experienced obstetrical anal sphincter injuries. In the model, factors independently associated with obstetrical anal sphincter injuries included use of forceps (adjusted odds ratio, 5.08; 95% confidence interval, 4.10-6.31) and vacuum assistance (adjusted odds ratio, 2.64; 95% confidence interval, 2.02-3.44), along with increasing maternal age (adjusted odds ratio, 1.05; 95% confidence interval, 1.04-1.07 per year), body mass index (adjusted odds ratio, 0.99; 95% confidence interval, 0.97-1.00 per unit kg/m2), previous vaginal delivery (adjusted odds ratio, 0.19; 95% confidence interval, 0.15-0.23), and tobacco use during pregnancy (adjusted odds ratio, 0.59; 95% confidence interval, 0.43-0.82). Internal validation demonstrated appropriate discrimination (concordance index, 0.790; 95% confidence interval, 0.771-0.808) and calibration (Brier score, 0.047). External validation used data from 1266 women who delivered at a tertiary healthcare system, with appropriate model discrimination (concordance index, 0.791; 95% confidence interval, 0.735-0.846) and calibration (Brier score, 0.046). The model can be accessed at oasisriskscore.xyz. Our model provided a robust, validated estimate of the probability of obstetrical anal sphincter injuries during vaginal birth after cesarean delivery using known antenatal risk factors and 1 modifiable intrapartum risk factor and can be used to counsel patients regarding risks of trial of labor after cesarean delivery compared with risks of elective repeat cesarean delivery.

Clock neurons gate memory extinction in Drosophila

Memory forms when a previously neutral stimulus (CS+) becomes competent to predict a biologically potent stimulus (US). However, if the CS+ is repeatedly presented without the US after the memory formation, this memory will be suppressed by newly formed extinction memory.1,2 The striking feature of extinction learning is that it requires repeated trials to robustly form extinction. Extended repetition only yields memories that remain transient in nature,3 thus imposing challenges in understanding the underlying mechanisms of extinction learning. Here, we took advantage of the versatile genetic tools4 and the well-characterized circadian system of Drosophila5,6 to link these unique features to clock neurons. We report that inhibiting the activity of clock neurons blocks the formation of extinction memory. Further investigation attributes this role to a subset of cryptochrome-positive dorsal neurons 1 (DN1s) and their downstream SIFamide neurons. The requirement of clock neurons from a gating mechanism of extinction for a single extinction learning trial robustly causes typical extinction when coupled with acute activation of DN1s, as marked by the initially enhanced but eventually diminished memory suppression. Accordingly, we detected specific neural responses to extinction training in a few DN1s via calcium imaging fulfilled by the TRIC tool,7 but not in dorsal neurons 2 or dorsolateral neurons. Based on these findings, we propose that in extinction of appetitive long-term memory, multiple trials of extinction learning robustly activate DN1 clock neurons to open the gate of extinction, which may contribute to the transient nature of extinction memory.

How time shapes cognitive control: A high-density EEG study of task-switching

Task-switching is one of the most popular paradigms to investigate cognitive control. The main finding of interest is the switch cost: RTs in switch trials are longer than RTs in repetition trials. Despite the massive amount of research in these topics, little is known about the underlying temporal dynamics of the cortical regions involved in these phenomena.Here we used high density EEG to unveil the spatiotemporal neural dynamics associated with both the switch cost and to its modulation over time (time-on-task effect), as two markers of cognitive control reflecting effortful and procedural mechanisms, respectively. We found that, as a function of task practice, the switch cost decreased and both the switch-positivity and the switch-negativity event-related responses increased, although the latter showed a larger modulatory effect. At a source level, this effect was revealed by a progressively higher activation of the left middle and superior frontal gyrus.

A hormetic approach to understanding antidepressant effectiveness and the development of antidepressant tolerance - A conceptual view.

Antidepressants such as the selective serotonin reuptake inhibitors (SSRIs) have complex temporal effects. They may worsen symptoms during early treatment, they may reduce depressive symptoms over several weeks of treatment, and they may lose effectiveness over more prolonged treatment or after repeated treatment trials. Conceptually, these effects fall within the domain of hormesis, which refers to a biphasic or multiphasic response to a drug or toxin. Hormetic effects are commonly triggered when a drug interacts with homeostatic mechanisms. We develop and evaluate a theoretical framework for understanding how adaptations to SSRIs that restore synaptic homeostasis may partially contribute to their hormetic effects. Specifically, the serotonin system adapts to SSRIs by suppressing the firing of serotonergic neurons, inhibiting the synthesis of serotonin, and reducing the overall content of serotonin in the brain. Moreover, rodent models such as inescapable shock show that serotonin neurotransmission to specific forebrain regions is a necessary, but insufficient cause of depressive symptoms. Our review suggests: (1) early worsening of symptoms may be related to the direct effects of SSRIs on synaptic serotonin; (2) the symptom-reducing effects could be related to the loss of serotonin content in the brain during SSRI exposure; (3) the loss of efficacy over prolonged exposure could be related to the central nervous system equilibrating to the SSRIs. The serotonin system's adaptations to SSRIs may play a clinically meaningful role in their hormetic effects on depressive symptoms. A complete understanding of SSRIs' hormetic effects will require exploring temporal dynamics in other neurotransmitter systems.

The Effect of Bilingualism on Cue-Based vs. Memory-Based Task Switching in Older Adults.

Findings suggest a positive impact of bilingualism on cognition, including the later onset of dementia. However, it is not clear to what extent these effects are influenced by variations in attentional control demands in response to specific task requirements. In this study, 20 bilingual and 20 monolingual older adults performed a task-switching task under explicit task-cuing vs. memory-based switching conditions. In the cued condition, task switches occurred in random order and a visual cue signaled the next task to be performed. In the memory-based condition, the task alternated after every second trial in a predictable sequence without presenting a cue. The performance of bilinguals did not vary across experimental conditions, whereas monolinguals experienced a pronounced increase in response latencies and error rates in the cued condition. Both groups produced similar switch costs (difference in performance on switch trials as opposed to repeating trials within the mixed-task block) and mixing costs (difference in performance on repeat trials of a mixed-task block as opposed to trials of a single-task block), but bilinguals produced them with lower response latencies. The cognitive benefits of bilingualism seem not to apply to executive functions per se but to affect specific cognitive processes that involve task-relevant context processing. The present results suggest that lifelong bilingualism could promote in older adults a flexible adjustment to environmental cues, but only with increased task demands. However, due to the small sample size, the results should be interpreted with caution.

Cognitive control in number processing: new evidence from task switching

Recently, it was demonstrated that even basic numerical cognition such as the processing of number magnitude is under cognitive control. However, evidence so far primarily came from adaptation effects to stimulus characteristics (e.g., relative frequency of specific stimulus categories). Expanding this approach, we evaluated a possible influence of more active exertion of cognitive control on basic number processing in task switching. Participants had to perform a magnitude comparison task while we manipulated the order of compatible and incompatible input–output modalities (i.e., auditory/vocal input–visual/manual output vs. auditory/visual input–manual/vocal output, respectively) on the trial level, differentiating repeat vs. switch trials. Results indicated that the numerical distance effect but not the problem size effect was increased after a switch in input–output modality compatibility. In sum, these findings substantiate that basic number processing is under cognitive control by providing first evidence that it is influenced by the active exertion of cognitive control as required in task switching.

Cross-sensory inhibition or unisensory facilitation: A potential neural architecture of modality switch effects

In a simple reaction time task in which auditory and visual stimuli are presented in random sequence alone (A or V) or together (AV), there is a so-called reaction time (RT) cost on trials in which sensory modality switches (A→V) compared to when it repeats (A→A). This is always true for unisensory trials, whereas RTs to AV stimuli preceded by unisensory stimuli are statistically comparable with the Repeat condition (AV→AV). Neural facilitation for Repeat trials or neural inhibition for Switch trials could both account for these effects. Here we used a neural network model (Multisensory Integration with Crossed Inhibitory Dynamics (MICID) model) to test the ability of these two distinct mechanisms, inhibition and facilitation, to produce the specific patterns of behavior that we see experimentally, modeling switch and repeat trials as well as the influence of the interval between the present and the previous trial. The model results are consistent with an inhibitory account in which there is competition between the different sensory modalities, instead of a facilitation account in which the preceding stimulus sensitizes the neural system to its particular sensory modality. Moreover, the model shows that multisensory integration can explain the results in case of multisensory stimuli, where the preceding stimulus has little effect. This is due to faster dynamics for multisensory facilitation compared to cross-sensory inhibition. These findings link the cognitive framework delineated by the empirical results to a plausible neural implementation.

Formative Evaluation of Consumer-Grade Activity Monitors Worn by Older Adults: Test-Retest Reliability and Criterion Validity of Step Counts.

BackgroundTo assess whether commercial-grade activity monitors are appropriate for measuring step counts in older adults, it is essential to evaluate their measurement properties in this population.ObjectiveThis study aimed to evaluate test-retest reliability and criterion validity of step counting in older adults with self-reported intact and limited mobility from 6 commercial-grade activity monitors: Fitbit Charge, Fitbit One, Garmin vívofit 2, Jawbone UP2, Misfit Shine, and New-Lifestyles NL-1000.MethodsFor test-retest reliability, participants completed two 100-step overground walks at a usual pace while wearing all monitors. We tested the effects of the activity monitor and mobility status on the absolute difference in step count error (%) and computed the standard error of measurement (SEM) between repeat trials. To assess criterion validity, participants completed two 400-meter overground walks at a usual pace while wearing all monitors. The first walk was continuous; the second walk incorporated interruptions to mimic the conditions of daily walking. Criterion step counts were from the researcher tally count. We estimated the effects of the activity monitor, mobility status, and walk interruptions on step count error (%). We also generated Bland-Altman plots and conducted equivalence tests.ResultsA total of 36 individuals participated (n=20 intact mobility and n=16 limited mobility; 19/36, 53% female) with a mean age of 71.4 (SD 4.7) years and BMI of 29.4 (SD 5.9) kg/m2. Considering test-retest reliability, there was an effect of the activity monitor (P<.001). The Fitbit One (1.0%, 95% CI 0.6% to 1.3%), the New-Lifestyles NL-1000 (2.6%, 95% CI 1.3% to 3.9%), and the Garmin vívofit 2 (6.0%, 95 CI 3.2% to 8.8%) had the smallest mean absolute differences in step count errors. The SEM values ranged from 1.0% (Fitbit One) to 23.5% (Jawbone UP2). Regarding criterion validity, all monitors undercounted the steps. Step count error was affected by the activity monitor (P<.001) and walk interruptions (P=.02). Three monitors had small mean step count errors: Misfit Shine (−1.3%, 95% CI −19.5% to 16.8%), Fitbit One (−2.1%, 95% CI −6.1% to 2.0%), and New-Lifestyles NL-1000 (−4.3%, 95 CI −18.9% to 10.3%). Mean step count error was larger during interrupted walking than continuous walking (−5.5% vs −3.6%; P=.02). Bland-Altman plots illustrated nonsystematic bias and small limits of agreement for Fitbit One and Jawbone UP2. Mean step count error lay within an equivalence bound of ±5% for Fitbit One (P<.001) and Misfit Shine (P=.001).ConclusionsTest-retest reliability and criterion validity of step counting varied across 6 consumer-grade activity monitors worn by older adults with self-reported intact and limited mobility. Walk interruptions increased the step count error for all monitors, whereas mobility status did not affect the step count error. The hip-worn Fitbit One was the only monitor with high test-retest reliability and criterion validity.

Tonically Active Neurons in the Monkey Dorsal Striatum Signal Outcome Feedback during Trial-and-error Search Behavior

An animal’s choice behavior is shaped by the outcome feedback from selected actions in a trial-and-error approach. Tonically active neurons (TANs), presumed cholinergic interneurons in the striatum, are thought to be involved in the learning and performance of reward-directed behaviors, but it remains unclear how TANs are involved in shaping reward-directed choice behaviors based on the outcome feedback. To this end, we recorded activity of TANs from the dorsal striatum of two macaque monkeys (Macaca fuscata; 1 male, 1 female) while they performed a multi-step choice task to obtain multiple rewards. In this task, the monkeys first searched for a rewarding target from among three alternatives in a trial-and-error manner and then earned additional rewards by repeatedly choosing the rewarded target. We found that a considerable proportion of TANs selectively responded to either the reward or the no-reward outcome feedback during the trial-and-error search, but these feedback responses were not observed during repeat trials. Moreover, the feedback responses of TANs were similarly observed in any search trials, without distinctions regarding the predicted probability of rewards and the location of chosen targets. Unambiguously, TANs detected reward and no-reward feedback specifically when the monkeys performed trial-and-error searches, in which the monkeys were learning the value of the targets and adjusting their subsequent choice behavior based on the reward and no-reward feedback. These results suggest that striatal cholinergic interneurons signal outcome feedback specifically during search behavior, in circumstances where the choice outcomes cannot be predicted with certainty by the animals.

Brain oscillatory activity associated with switch and mixing costs during reactive control.

Task-switching paradigms, which involve task repetitions and between-task switches, have long been used as a benchmark of cognitive control processes. When mixed and single-task blocks are presented, two types of costs usually occur: the switch cost, measured by contrasting performance on switch and repeat trials during the mixed-task blocks, and the mixing cost, calculated as the performance difference between the all-repeat trials from the single-task blocks and the repeat trials from the mixed-task blocks. Both costs can be mitigated by informational cues that signal the upcoming task switch beforehand. Recent electroencephalographic studies have started unveiling the brain oscillatory activity underlying the switch cost during the preparatory cue-target interval, thus, targeting proactive control processes. Less attention has instead been paid to the mixing cost and, importantly, to the oscillatory dynamics involved in switch and mixing costs during reactive control. To fill this gap, here, we analyzed the time-frequency data obtained during a task-switching paradigm wherein the simultaneous presentation of task cues and targets increased the need for reactive control. Results showed that while alpha and beta bands were modulated by switch and mixing costs in a similar gradual fashion, with greater suppression going from switch to repeat and all-repeat trials, theta power was sensitive to the switch cost with increased power for switch than repeat trials. Together, our findings join previous studies underlining the importance of theta, alpha and beta oscillations in task-switching and extend them by depicting the oscillations involved in switch and mixing costs during reactive control processes.

Intra-session and inter-rater reliability of spatial frequency analysis methods in skeletal muscle.

Spatial frequency analysis (SFA) is a quantitative ultrasound (US) method originally developed to assess intratendinous tissue structure. This method may also be advantageous in assessing other musculoskeletal tissues. Although SFA has been shown to be a reliable assessment strategy in tendon tissue, its reliability in muscle has not been investigated. The purpose of this study was to examine the reliability of spatial frequency parameter measurement for a large muscle group within a healthy population. Ten participants with no history of lower extremity surgery or hamstring strain injury volunteered. Longitudinal B-mode images were collected in three different locations across the hamstring muscles. Following a short rest, the entire imaging procedure was repeated. B-mode images were processed by manually drawing a region of interest (ROI) about the entire muscle thickness. Four spatial frequency parameters of interest were extracted from the image ROIs. Intra- and inter-rater reliabilities of extracted SFA parameters were performed. Test-retest reliability of the image acquisition procedure was assessed between repeat trials. Intraclass correlation coefficients showed high intra- and inter-rater reliability (ICC(3,1) > 0.9 for all parameters) and good to moderate test-retest reliability (ICC(3,1) > 0.50) between trials. No differences in parameter values were observed between trials across all muscles and locations (p > 0.05). The high reliability metrics suggest that SFA will be useful for future studies assessing muscle tissue structure, and may have value in assessing muscular adaptations following injury and during recovery.

Switching Competitors Reduces Win-Stay but Not Lose-Shift Behaviour: The Role of Outcome-Action Association Strength on Reinforcement Learning

Predictability is a hallmark of poor-quality decision-making during competition. One source of predictability is the strong association between current outcome and future action, as dictated by the reinforcement learning principles of win–stay and lose–shift. We tested the idea that predictability could be reduced during competition by weakening the associations between outcome and action. To do this, participants completed a competitive zero-sum game in which the opponent from the current trial was either replayed (opponent repeat) thereby strengthening the association, or, replaced (opponent change) by a different competitor thereby weakening the association. We observed that win–stay behavior was reduced during opponent change trials but lose–shiftbehavior remained reliably predictable. Consistent with the group data, the number of individuals who exhibited predictable behavior following wins decreased for opponent change relative to opponent repeat trials. Our data show that future actions are more under internal control following positive relative to negative outcomes, and that externally breaking the bonds between outcome and action via opponent association also allows us to become less prone to exploitation.

Mild Cognitive Impairments Attenuate Prefrontal Cortex Activations during Walking in Older Adults.

The presence of Mild Cognitive Impairments (MCI) is associated with worse gait performance. However, the effect of MCI on cortical control of gait, as assessed during active walking, is unknown. We hypothesized that MCI would be associated with attenuated activations and limited improvement in efficiency in the Prefrontal cortex (PFC) under cognitively-demanding walking conditions. Functional Near-Infrared Spectroscopy (fNIRS) was used to assess Oxygenated Hemoglobin (HbO2) in the PFC during Single-Task-Walk (STW), cognitive interference (Alpha) and Dual-Task-Walk (DTW) conditions. Three repeated trials in each experimental condition were administered. Healthy control (n = 71; mean age = 76.82 ± 6.21 years; %female = 50.7) and MCI (n = 11; mean age = 78.27 ± 4.31 years; %female = 45.5) participants were included. The increase in HbO2 from STW to DTW was attenuated among MCI participants compared to controls (estimate = 0.505; p = 0.001). Whereas, among controls, HbO2 increased from Alpha to DTW, the opposite was observed among MCI participants (estimate = 0.903; p < 0.001). In DTW, the decline in HbO2 from trial 1 to 2 was attenuated in MCI participants compared to controls (estimate = 0.397; p = 0.008). Moreover, whereas HbO2 declined from trial 1 to 3 among controls, MCI participants showed the opposite trend (estimate = 0.946; p < 0.001). MCI was associated with attenuated brain activation patterns and compromised ability to improve PFC efficiency during dual-task walking.