Improving community walking after stroke; the effect of dual task treadmill training on gait, cognition and brain control mechanisms of dual task walking in chronic stroke survivors

It is well known that improving community walking ability is one of the major goals in stroke rehabilitation. Even if motor recovery of the lower limbs does occur, the ability to walk in the community is often still impaired. This thesis set out to explore dual task ability after stroke in relation to community walking and explored dual task treadmill training in stroke survivors. In addition, functional magnetic resonance imaging (fMRI) and functional near-infrared spectroscopy (fNIRS) in stroke survivors during single and dual gait movements were performed to examine dual task effects on brain activation before and after dual task training. In a cross-sectional trial, 27 limited community walkers were compared to 23 moderate-to-full community walkers. A significant larger proportion of limited community walkers were not confident about walking in the community compared to moderate-to-full community walkers (p = 0.042). Moreover mean cognitive response during two-minute-walk with dual task was 11.17 ± 3.62 for limited walkers and 13.48 ± 2.43 for moderate-to-full community walkers (p = 0.014). In contrast, moderate-to-full community walkers displayed relative larger reductions in walking distance as a result of dual task in comparison to limited community walkers (p = 0.068). Consequently, a randomized controlled trial was performed in 50 chronic stroke survivors to explore to what extent 10 weeks of treadmill training with concurrent cognitive distraction in comparison to 10 weeks of treadmill training with no distraction would change community walking ability. Stroke survivors who received dual task treadmill training showed larger increases in two-minute-walk distance compared to the control group from baseline to follow with an effect size r of 0.24 and a Cohen’s d of 0.50. Significant group and time interactions were seen for physical activity scale assessments favouring the dual task training group (p = 0.029). In addition, on a modified version of the University of Alabama study of Aging Life Space Assessment questionnaire, stroke survivors in the dual task training group scored 54.76 ± 26.64 compared to 41.53 ± 20.88 in the control group at follow-up, (p = 0.086). Both training groups improved on walking performance and endurance during training. Feasibility of dual task training was good, with only l0% drop out for intention to treat. The final part of this thesis focussed on results from fMRI and fNIRS measures that were taken to explore brain activation patterns during single and dual task gait before and after dual task training. At baseline, decreases in brain activation were seen in prefrontal cortex areas during dual task treadmill walking compared to single task treadmill walking. Moreover, fMRI during pedal movements with a concurrent cognitive task showed decreased brain activation compared to pedal movement alone. Dual task trained stroke survivors showed a reduction in right occipital cortex activation during pedalling at follow-up compared to baseline whereas control trained stroke survivors showed increases in this area from baseline to follow-up with a significant difference of activation change between groups (p < 0.001). In addition, stroke survivors who had received dual task training showed significant reductions in brain activation during pedalling and increase in activation during dual task pedalling from baseline to follow-up. The results from the comparisons between limited community walkers and moderate-to-full community walkers suggested that different coping strategies might apply after stroke depending on gait speed, but also indicated that both type of community walkers had difficulties with dual task walking. Dual task treadmill training showed good feasibility and positive effects on walking endurance and performance as well as training without distraction. There were trends suggesting that stroke survivors who were already physically active and had recovered their walking up to a certain standard were more likely to improve their dual task walking distance after dual training. Brain imaging measures showed decreases in activation from single to dual task locomotor movements which may relate to reduced dual task ability in stroke survivors, but these changes did not correlate with changes in behavioural measures of dual task. The changes in response to training may relate to plasticity and a recovery of the automaticity of control of normal walking as a result of dual task training. This thesis has provided novel research, insights and practical implications for dual task training after stroke. More research is needed, for instance to explore the extent to which stroke survivors could benefit from dual task training in more real-life situations. The use of neuroimaging tools in stroke rehabilitation trials helps to understand how motor control mechanisms change in response to training and could add to tailor rehabilitation to the individual’s need

Neural substrates of cognitive motor interference during walking: Peripheral and central mechanisms

Current gait control models suggest that independent locomotion depends on central and peripheral mechanisms. However, less information is available on the integration of these mechanisms for adaptive walking. In this cross-sectional study, we investigated gait control mechanisms in people with Parkinson’s disease (PD) and healthy older (HO) adults: at self-selected walking speed (SSWS) and at fast walking speed (FWS). We measured effect of additional cognitive task (DT) and increased speed on prefrontal (PFC) and motor cortex (M1) activation, and Soleus H-reflex gain. Under DT-conditions we observed increased activation in PFC and M1. Whilst H-reflex gain decreased with additional cognitive load for both groups and speeds, H-reflex gain was lower in PD compared to HO while walking under ST condition at SSWS. Attentional load in PFC excites M1, which in turn increases inhibition on H-reflex activity during walking and reduces activity and sensitivity of peripheral reflex during the stance phase of gait. Importantly this effect on sensitivity was greater in HO. We have previously observed that the PFC copes with increased attentional load in young adults with no impact on peripheral reflexes and we suggest that gait instability in PD may in part be due to altered sensorimotor functioning reducing the sensitivity of peripheral reflexes

Associations between prefrontal cortex activation and H-reflex modulation during dual task gait

Walking, although a largely automatic process, is controlled by the cortex and the spinal cord with corrective reflexes modulated through integration of neural signals from central and peripheral inputs at supraspinal level throughout the gait cycle. In this study we used an additional cognitive task to interfere with the automatic processing during walking in order to explore the neural mechanisms involved in healthy young adults. Participants were asked to walk on a treadmill at two speeds, both with and without additional cognitive load. We evaluated the impact of speed and cognitive load by analysing activity of the pre-frontal cortex (PFC) using functional Near-Infrared Spectroscopy (fNIRS) alongside spinal cord reflex activity measured by soleus H-reflex amplitude and gait changes obtained by using an inertial measuring unit. Repeated measures ANOVA revealed that fNIRS Oxy-Hb concentrations significantly increased in the PFC with dual task (walking while performing a cognitive task) compared to a single task only (walking) (p<0.05). PFC activity was unaffected by increases of walking speed. H-reflex amplitude and gait variables did not change in response to either dual task or increases in walking speed. When walking under additional cognitive load participants adapted by using greater activity in the PFC, but this adaption did not detrimentally affect H-reflex amplitude or gait variables. Our findings suggests that in a healthy young population central mechanisms (PFC) are activated in response to cognitive loads but that H-reflex activity and gait performance can successfully be maintained. This study provides insights into the mechanisms behind healthy individuals safely performing dual task walking

Neural Substrates of Cognitive Motor Interference During Walking; Peripheral and Central Mechanisms

Current gait control models suggest that independent locomotion depends on central and peripheral mechanisms. However, less information is available on the integration of these mechanisms for adaptive walking. In this cross-sectional study, we investigated gait control mechanisms in people with Parkinson’s disease (PD) and healthy older (HO) adults: at self-selected walking speed (SSWS) and at fast walking speed (FWS). We measured effect of additional cognitive task (DT) and increased speed on prefrontal (PFC) and motor cortex (M1) activation, and Soleus H-reflex gain. Under DT-conditions we observed increased activation in PFC and M1. Whilst H-reflex gain decreased with additional cognitive load for both groups and speeds, H-reflex gain was lower in PD compared to HO while walking under ST condition at SSWS. Attentional load in PFC excites M1, which in turn increases inhibition on H-reflex activity during walking and reduces activity and sensitivity of peripheral reflex during the stance phase of gait. Importantly this effect on sensitivity was greater in HO. We have previously observed that the PFC copes with increased attentional load in young adults with no impact on peripheral reflexes and we suggest that gait instability in PD may in part be due to altered sensorimotor functioning reducing the sensitivity of peripheral reflexes

A randomised controlled trial of a walking training with simultaneous cognitive demand (dual task) in chronic stroke

Objective. To evaluate the tolerability of, adherence to and efficacy of a community walking training programme with simultaneous cognitive demand (dual‐task) compared to a control walking training programme without cognitive distraction. Methods. Adult stroke survivors, at least 6 months after stroke with a visibly obvious gait abnormality or reduced two‐minute walk distance were included into a 2‐arm parallel randomized controlled trial of complex intervention with blinded assessments. Participants received a 10 week, bi‐weekly, 30 minutes treadmill program at an aerobic training intensity (55‐85% heart rate maximum), either with, or without simultaneous cognitive demands. Outcome measured at 0, 11 and 22 weeks. Primary: two‐minute‐walk tests with and without cognitive distraction, dual task effect on walking and cognition; secondary: SF‐36, EuroQol‐5D‐5L, Physical Activity Scale for Elderly (PASE), and step activity. Results. Fifty stroke patients were included, 43 received allocated training and 45 completed all assessments. The experimental group (n = 26) increased mean (SD) two‐minute walking distance from 90.7 (8.2) to 103.5 (8.2) metres, compared with 86.7 (8.5) to 92.8 (8.6) in the control group, and their PASE score from 74.3 (9.1) to 89.9 (9.4), compared with 94.7 (9.4) to 77.3 (9.9) in the control group. Statistically, only the change in the PASE differed between the groups (p = 0.029), with the dual‐task group improving more. There were no differences in other measures. Conclusions. Walking with specific additional cognitive distraction (dual‐task training) might increase activity more over 12 weeks, but the data are not conclusive

Dual-task walking and automaticity after stroke: Insights from a secondary analysis and imaging sub-study of a randomised controlled trial

Objective. To test the extent to which initial walking speed influences dual-task performance after walking intervention, hypothesising that slow walking speed affects automatic gait control, limiting executive resource availability. Design. A secondary analysis of a trial of dual-task (DT) and single-task (ST) walking interventions comparing those with good (walking speed ⩾0.8 m s−1, n = 21) and limited (walking speed <0.79 m s−1, n = 24) capacity at baseline. Setting. Community. Subjects. Adults six-months post stroke with walking impairment. Interventions. Twenty sessions of 30 minutes treadmill walking over 10 weeks with (DT) or without (ST) cognitive distraction. Good and limited groups were formed regardless of intervention received. Main measures. A two-minute walk with (DT) and without (ST) a cognitive distraction assessed walking. fNIRS measured prefrontal cortex activation during treadmill walking with (DT) and without (ST) Stroop and planning tasks and an fMRI sub-study used ankle-dorsiflexion to simulate walking. Results. ST walking improved in both groups (∆baseline: Good = 8.9 ± 13.4 m, limited = 5.3±8.9 m, Group × time = P < 0.151) but only the good walkers improved DT walking (∆baseline: Good = 10.4 ± 13.9 m, limited = 1.3 ± 7.7 m, Group × time = P < 0.025). fNIRS indicated increased ispilesional prefrontal cortex activation during DT walking following intervention (P = 0.021). fMRI revealed greater DT cost activation for limited walkers, and increased resting state connectivity of contralesional M1 with cortical areas associated with conscious gait control at baseline. After the intervention, resting state connectivity between ipsilesional M1 and bilateral superior parietal lobe, involved in integrating sensory and motor signals, increased in the good walkers compared with limited walkers. Conclusion. In individuals who walk slowly it may be difficult to improve dual-task walking ability

Urbanization drives community shifts towards thermophilic and dispersive species at local and landscape scales

The increasing conversion of agricultural and natural areas to human-dominated urban landscapes is predicted to lead to a major decline in biodiversity worldwide. Two conditions that typically differ between urban environments and the surrounding landscape are increased temperature, and high patch isolation and habitat turnover rates. However, the extent and spatial scale at which these altered conditions shape biotic communities through selection and/or filtering on species traits are currently poorly understood. We sampled carabid beetles at 81 sites in Belgium using a hierarchically nested sampling design wherein three local-scale (200 × 200 m) urbanization levels were repeatedly sampled across three landscape-scale (3 × 3 km) urbanization levels. First, we showed that communities sampled in the most urbanized locations and landscapes displayed a distinct species composition at both local and landscape scale. Second, we related community means of species-specific thermal preferences and dispersal capacity (based on European distribution and wing morphology, respectively) to the urbanization gradients. We showed that urban communities consisted on average of species with a preference for higher temperatures and with better dispersal capacities compared to rural communities. These shifts were caused by an increased number of species tolerating higher temperatures, a decreased richness of species with low thermal preference, and an almost complete depletion of species with very low-dispersal capacity in the most urbanized localities. Effects of urbanization were most clearly detected at the local scale, although more subtle effects could also be found at the scale of entire landscapes. Our results demonstrate that urbanization may fundamentally and consistently alter species composition by exerting a strong filtering effect on species dispersal characteristics and favouring replacement by warm-dwelling species.status: publishe

Faecal occult blood loss accurately predicts future detection of colorectal cancer. A prognostic model

Objectives To examine the prognostic potential of repeated faecal haemoglobin (F-Hb) concentration measurements in faecal immunochemical test (FIT)-based screening for colorectal cancer (CRC). Design Prognostic model. Setting Dutch biennial FIT-based screening programme during 2014-2018. Participants 265 881 participants completing three rounds of FIT, with negative test results (F-Hb <47 μg Hb/g faeces) in rounds 1 and 2. Interventions Colonoscopy follow-up in participants with a positive FIT (F-Hb ≥47 μg Hb/g faeces). Main outcomes We evaluated prognostic models for detecting advanced neoplasia (AN) and CRC in round 3, with as predictors, participant age, sex, F-Hb in rounds 1 and 2, and categories/combinations/non-linear transformations of F-Hb. Primary evaluation criteria included: risk prediction accuracy (calibration), discrimination of participants with versus without AN or CRC (optimism-adjusted C-statistics, range 0.5-1.0), the degree of risk stratification and C-statistics in external validation. Results Among study participants, 8806 (3.3%) had a positive FIT result, 3254 (1.2%) had AN detected and 557 (0.2%) had cancer. F-Hb concentrations in rounds 1 and 2 were the strongest outcome predictors, with adjusted ORs of up to 9.4 (95% CI 7.5 to 11.7) for the highest F-Hb category. Risk predictions matched the observed risk for most participants (calibration intercept -0.008 to -0.099; slope 0.982-0.998), and discriminated participants with versus without AN or CRC with C-statistics of 0.78 (95% CI 0.77 to 0.79) and 0.73 (95% CI 0.71 to 0.75), respectively. The predicted risk ranged from 0.4% to 36.7% for AN and from 0.0% to 5.5% for CRC across participants. In external validation, the model retained similar discrimination accuracy for AN (C-statistic 0.77, 95% CI 0.66 to 0.87) and CRC (C-statistic 0.78, 95% CI 0.66 to 0.91). Conclusion Participants at lower versus higher risk of future AN or CRC can be accurately identified based on their age, sex and particularly, prior F-Hb concentrations. Risk stratification should be considered based on this information