A Dynamical Systems Approach to Characterizing Brain-Body Interactions during Movement: Challenges, Interpretations, and Recommendations.

Brain-body interactions (BBIs) have been the focus of intense scrutiny since the inception of the scientific method, playing a foundational role in the earliest debates over the philosophy of science. Contemporary investigations of BBIs to elucidate the neural principles of motor control have benefited from advances in neuroimaging, device engineering, and signal processing. However, these studies generally suffer from two major limitations. First, they rely on interpretations of 'brain' activity that are behavioral in nature, rather than neuroanatomical or biophysical. Second, they employ methodological approaches that are inconsistent with a dynamical systems approach to neuromotor control. These limitations represent a fundamental challenge to the use of BBIs for answering basic and applied research questions in neuroimaging and neurorehabilitation. Thus, this review is written as a tutorial to address both limitations for those interested in studying BBIs through a dynamical systems lens. First, we outline current best practices for acquiring, interpreting, and cleaning scalp-measured electroencephalography (EEG) acquired during whole-body movement. Second, we discuss historical and current theories for modeling EEG and kinematic data as dynamical systems. Third, we provide worked examples from both canonical model systems and from empirical EEG and kinematic data collected from two subjects during an overground walking task.

Salivary S100 calcium-binding protein beta (S100B) and neurofilament light (NfL) after acute exposure to repeated head impacts in collegiate water polo players.

Blood-based biomarkers of brain injury may be useful for monitoring brain health in athletes at risk for concussions. Two putative biomarkers of sport-related concussion, neurofilament light (NfL), an axonal structural protein, and S100 calcium-binding protein beta (S100B), an astrocyte-derived protein, were measured in saliva, a biofluid which can be sampled in an athletic setting without the risks and burdens associated with blood sampled by venipuncture. Samples were collected from men's and women's collegiate water polo players (n = 65) before and after a competitive tournament. Head impacts were measured using sensors previously evaluated for use in water polo, and video recordings were independently reviewed for the purpose of validating impacts recorded by the sensors. Athletes sustained a total of 107 head impacts, all of which were asymptomatic (i.e., no athlete was diagnosed with a concussion or more serious). Post-tournament salivary NfL was directly associated with head impact frequency (RR = 1.151, p = 0.025) and cumulative head impact magnitude (RR = 1.008, p = 0.014), while controlling for baseline salivary NfL. Change in S100B was not associated with head impact exposure (RR < 1.001, p > 0.483). These patterns suggest that repeated head impacts may cause axonal injury, even in asymptomatic athletes.

Head impact exposure and concussion in women's collegiate club lacrosse.

This study sought to describe head impact exposure in women's collegiate club lacrosse. Eleven women's collegiate club lacrosse players wore head impact sensors during eight intercollegiate competitions. Video recordings of competitions were used to verify impact data. Athletes completed questionnaires detailing their concussion history and perceived head impact exposure. During the monitored games, no diagnosed concussions were sustained. Three athletes reported sustaining head impacts (median = 0; range: 0-3 impacts per game). Six impacts registered by the sensors were verified on video across a total of 81 athlete-game exposures. Verified impacts had a median peak linear acceleration of 21.0 g (range: 18.3 g - 48.3 g) and peak rotational acceleration of 1.1 krad/s2 (range: 0.7 krad/s2 - 5.7 krad/s2). Women competing in collegiate club lacrosse are at a low risk of sustaining head impacts, comparable to previous reports of the high school and collegiate varsity levels of play.

Dynamic associations between anxiety, depression, and tobacco use in older adults: Results from The Irish Longitudinal Study on Ageing.

Evidence supports moderate-to-large reductions in anxiety, depression, and perceived stress after smoking cessation; however, much of the available evidence has focused on young adults. Therefore, this study quantified associations between smoking and smoking cessation on prevalent and incident generalised anxiety disorder (GAD) and major depression (MDD) in a nationally representative sample of Irish older adults. Participants (n = 6201) were community dwelling adults aged ≥50 years resident in Ireland. Smoking status and self-reported doctor diagnosis of anxiety or depression prior to baseline were assessed at baseline (i.e., Wave 2). At baseline and 2-, 4-, and 6-year follow-up (i.e., Waves 3-5), GAD and MDD were assessed by the Composite International Diagnostic Interview Short-Form. Logistic regression quantified cross-sectional and prospective associations (odds ratios (ORs) and 95% confidence intervals (95%CIs)) between smoking status and mental health. Prevalence and incidence of GAD was 9.1% (n = 566) and 2.8% (n = 148), respectively. Prevalence and incidence of depression was 11.1% (n = 686) and 6.4% (n = 342), respectively. Following full adjustment, current smokers had higher odds of prevalent GAD (OR = 1.729, 1.332-2.449; p < 0.001) and MDD (OR = 1.967, 1.548-2.499; p < 0.001) than non-smokers. Former smokers had higher odds of prevalent GAD than non-smokers (OR = 1.276, 1.008-1.616; p < 0.001). Current smokers did not have higher odds of incident MDD (OR = 1.399, 0.984-1.990; p = 0.065) or GAD than non-smokers (1.039, 0.624-1.730; p = 0.881). Findings may have important implications for interventions designed to curb tobacco abuse, which tend to be less successful among those with anxiety and depression.

The Association Between Generalized Anxiety Disorder and Resting-State Prefrontal Cortex Oxygenation Is Modified by Self-Reported Physical Activity: Results From The Irish Longitudinal Study on Ageing.

Individuals with anxiety disorders exhibit lower intrinsic functional connectivity between prefrontal cortical areas and subcortical regions. The prefrontal cortex (PFC) is sensitive to the acute and chronic effects of physical activity (PA), while the anxiolytic effects of PA are well known. The current study examined the association of generalized anxiety disorder (GAD) and its interaction with PA, with resting-state, left PFC oxygenation. This cross-sectional study used data from participants (N = 2444) from The Irish Longitudinal Study on Ageing, a nationally representative prospective study of community-living adults aged 50 and older in Ireland. The Composite International Diagnostic Interview Short-Form determined fulfillment of criteria for GAD. The short-form International Physical Activity Questionnaire determined adherence to the World Health Organization PA guidelines. Resting-state, left PFC oxygenation was continuously measured via a Portalite. Tissue saturation index (TSI) was calculated as the ratio of oxygenated hemoglobin to total tissue hemoglobin (expressed as a percentage) for the final minute of a 5-minute supine-rest period. Multivariable linear regression quantified associations of GAD with TSI in the total population and population stratified by PA status. Participants with GAD had lower TSI (b = -1.416, p = .008) compared to those without GAD. However, this association was modified by PA. Among participants who met the PA guidelines, TSI did not differ according to GAD status (b = -0.800, p = .398). For participants who did not meet the guidelines, TSI was significantly lower among those with GAD (b = -1.758, p = .004). These findings suggest that PA may help to protect brain health among older adults with GAD.

Age-Related Trajectories of Brain Structure-Function Coupling in Female Roller Derby Athletes.

Contact and collision sports are believed to accelerate brain aging. Postmortem studies of the human brain have implicated tau deposition in and around the perivascular space as a biomarker of an as yet poorly understood neurodegenerative process. Relatively little is known about the effects that collision sport participation has on the age-related trajectories of macroscale brain structure and function, particularly in female athletes. Diffusion MRI and resting-state functional MRI were obtained from female collision sport athletes (n = 19 roller derby (RD) players; 23-45 years old) and female control participants (n = 14; 20-49 years old) to quantify structural coupling (SC) and decoupling (SD). The novel and interesting finding is that RD athletes, but not controls, exhibited increasing SC with age in two association networks: the frontoparietal network, important for cognitive control, and default-mode network, a task-negative network (permuted p = 0.0006). Age-related increases in SC were also observed in sensorimotor networks (RD, controls) and age-related increases in SD were observed in association networks (controls) (permuted p ≤ 0.0001). These distinct patterns suggest that competing in RD results in compressed neuronal timescales in critical networks as a function of age and encourages the broader study of female athlete brains across the lifespan.

Physical activity partially mediates associations between "Big" personality traits and incident generalized anxiety disorder: Findings from the irish longitudinal study on ageing.

BACKGROUND: This study aimed to examine associations of personality with generalized anxiety disorder (GAD) and physical activity (PA), PA with GAD, and PA mediates associations between personality and incident GAD. METHODS: Participants aged ≥50 years completed the 60-item NEO-Five Factor Inventory questionnaire to assess personality and short-form International Physical Activity Questionnaire at baseline, and the Composite International Diagnostic Interview - Short Form to clinically assess GAD at baseline and 2, 4, and 6 years later. Participants who had GAD at baseline or reported having ever been told by a doctor that they had anxiety were excluded from analyses. Binary logistic regression quantified associations of the 'Big Five' personality traits with PA and incident GAD, and associations of PA with incident GAD (i.e., GAD at any point during follow-up). The 'counterfactual approach' identified potential mediating effects of PA in the associations between personality traits and incident GAD. RESULTS: Participants (n = 4582; 53.7% female) were aged 64.38±8.88 years. Incidence of GAD was 2.95% (n = 135). Extraversion (OR=1.160, 95%CI=1.087-1.237), openness (1.113, 1.043-1.188), and conscientiousness (1.083, 1.015-1.155) were positively associated with physical activity. Neuroticism was positively (2.335, 1.945-2.803), and extraversion (0.700, 0.563-0.797), conscientiousness (0.826, 0.693-0.985), and PA (0.655, 0.451-0.952) were inversely, associated with the incident GAD. Approximately 8.7% of the effect of extraversion and 8.8% of the effect of conscientiousness on GAD was due to mediation by PA only. LIMITATIONS: PA was self-reported Conclusions: Personality screening may help to identify older adults at-risk of anxiety who would benefit from participation in physical activity interventions.

One season of head-to-ball impact exposure alters functional connectivity in a central autonomic network.

Repetitive head impacts represent a risk factor for neurological impairment in team-sport athletes. In the absence of symptoms, a physiological basis for acute injury has not been elucidated. A basic brain function that is disrupted after mild traumatic brain injury is the regulation of homeostasis, instantiated by activity across a specific set of brain regions that comprise a central autonomic network. We sought to relate head-to-ball impact exposure to changes in functional connectivity in a core set of central autonomic regions and then to determine the relation between changes in brain and changes in behavior, specifically cognitive control. Thirteen collegiate men's soccer players and eleven control athletes (golf, cross-country) underwent resting-state fMRI and behavioral testing before and after the season, and a core group of cortical, subcortical, and brainstem regions was selected to represent the central autonomic network. Head-to-ball impacts were recorded for each soccer player. Cognitive control was assessed using a Dot Probe Expectancy task. We observed that head-to-ball impact exposure was associated with diffuse increases in functional connectivity across a core CAN subnetwork. Increased functional connectivity between the left insula and left medial orbitofrontal cortex was associated with diminished proactive cognitive control after the season in those sustaining the greatest number of head-to-ball impacts. These findings encourage measures of autonomic physiology to monitor brain health in contact and collision sport athletes.

Patterns of head impact exposure in men's and women's collegiate club water polo.

OBJECTIVES: Recent reports have demonstrated a risk of concussion and subconcussive head impacts in collegiate varsity and international elite water polo. We sought to characterize patterns of head impact exposure at the collegiate club level of water polo. DESIGN: Prospective cohort study. METHODS: Head impact sensors (SIM-G, Triax Technologies) were worn by men's (n=16) and women's (n=15) collegiate club water polo players during 11 games. Peak linear acceleration (PLA) and peak rotational acceleration (PRA) of head impacts were recorded by the sensors. Two streams of competition video were used to verify and describe the nature of head impacts. RESULTS: Men's players sustained 52 verified head impacts of magnitude 39.7±16.3g PLA and 5.2±3.2 krad/s2 PRA, and women's players sustained 43 verified head impacts of magnitude 33.7±12.6g PLA and 4.0±2.8krad/s2 PRA. Impacts sustained by men had greater PLA than those sustained by women (p=.045). Athletes were impacted most frequently at the offensive center position, to the back of the head, and by an opponent's torso or limb. CONCLUSIONS: Our cohort of male and female athletes sustained relatively infrequent head impacts during water polo competitions played at the collegiate club level. The amount of head impact exposure in our cohort was dependent on player position, with offensive centers prone to sustaining the most impacts. Head impact sensors are subject to large amounts of false positives and should be used in conjunction with video recordings to verify the validity of impact data.

A Dose Relationship Between Brain Functional Connectivity and Cumulative Head Impact Exposure in Collegiate Water Polo Players.

A growing body of evidence suggests that chronic, sport-related head impact exposure can impair brain functional integration and brain structure and function. Evidence of a robust inverse relationship between the frequency and magnitude of repeated head impacts and disturbed brain network function is needed to strengthen an argument for causality. In pursuing such a relationship, we used cap-worn inertial sensors to measure the frequency and magnitude of head impacts sustained by eighteen intercollegiate water polo athletes monitored over a single season of play. Participants were evaluated before and after the season using computerized cognitive tests of inhibitory control and resting electroencephalography. Greater head impact exposure was associated with increased phase synchrony [r (16) > 0.626, p < 0.03 corrected], global efficiency [r (16) > 0.601, p < 0.04 corrected], and mean clustering coefficient [r (16) > 0.625, p < 0.03 corrected] in the functional networks formed by slow-wave (delta, theta) oscillations. Head impact exposure was not associated with changes in performance on the inhibitory control tasks. However, those with the greatest impact exposure showed an association between changes in resting-state connectivity and a dissociation between performance on the tasks after the season [r (16) = 0.481, p = 0.043] that could also be attributed to increased slow-wave synchrony [F (4, 135) = 113.546, p < 0.001]. Collectively, our results suggest that athletes sustaining the greatest head impact exposure exhibited changes in whole-brain functional connectivity that were associated with altered information processing and inhibitory control.

The effects of exercise on mood and prefrontal brain responses to emotional scenes in smokers.

The benefits of exercise for smokers attempting to quit are partially dependent on physical activity levels prior to cessation. Mood disturbances can manifest within 30 min of smoking a cigarette and contribute to negative reinforcement of smoking behavior over time, whereas a single bout of aerobic exercise can reduce negative mood states and improve affect on a similar timescale in non-smokers. The acute effects of exercise among non-abstaining smokers immediately after a cigarette are unknown but may have clinical implications for smokers considering cessation. The aim of this study was to examine the concurrent effects of exercise on mood disturbance and prefrontal brain hemodynamic response to emotionally arousing scenes 30 min after smoking a cigarette and to test whether prefrontal brain hemodynamic response was correlated with affective ratings of the scenes. Fifteen cigarette smokers, averaging 47.6 cigarettes/week in the year prior to screening, served as participants. Functional near-infrared spectroscopy was used to measure hemodynamic status over the dorsolateral prefrontal cortex (DLPFC). Participants viewed pleasant, unpleasant, and neutral scenes prior to smoking a cigarette and 30 min later after seated rest or exercise at a preferred intensity. Mood disturbance was assessed by the Profile of Mood States-Brief Form four times: before smoking a cigarette, before and after exercise and rest, and after a post-condition (exercise/rest) exposure to emotionally arousing scenes. Compared to seated rest, cycling after a cigarette reduced mood disturbance (p = =.038) and DLPFC hemodynamic response to unpleasant (p = =.003) and pleasant (p = =.021) scenes relative to neutral scenes. DLPFC hemodynamic response was not related to affective ratings of scenes. We report that cycling for 20 min at a preferred intensity reduces mood disturbances which occur shortly after smoking a cigarette and blunts DLPFC hemodynamic response to emotionally arousing scenes. The findings encourage further investigation of exercise for smokers in the maintenance stage of smoking cessation.

Speckleplethysmographic (SPG) Estimation of Heart Rate Variability During an Orthostatic Challenge.

Heart rate variability (HRV) provides insight into cardiovascular health and autonomic function. Electrocardiography (ECG) provides gold standard HRV measurements but is inconvenient for continuous acquisition when monitored from the extremities. Optical techniques such as photoplethysmography (PPG), often found in health and wellness trackers for heart rate measurements, have been used to estimate HRV peripherally but decline in accuracy during increased physical stress. Speckleplethysmography (SPG) is a recently introduced optical technique that provides benefits over PPG, such as increased signal amplitude and reduced susceptibility to temperature-induced vasoconstriction. In this research, we compare SPG and PPG to ECG for estimation of HRV during an orthostatic challenge performed by 17 subjects. We find that SPG estimations of HRV are highly correlated to ECG HRV for both time and frequency domain parameters and provide increased accuracy over PPG estimations of HRV. The results suggest SPG measurements are a viable alternative for HRV estimation when ECG measurements are impractical.

Head impacts sustained by male collegiate water polo athletes.

Water polo is a contact sport that is gaining popularity in the United States and carries a risk of repeated head impacts and concussion. The frequency and magnitude of sport-related head impacts have not been described for water polo. We aimed to compare patterns of empirically measured head impact exposure of male collegiate water polo players to patterns previously reported by a survey of current and former water polo athletes. Participants wore water polo caps instrumented with head impact sensors during three seasons of collegiate water polo. Peak linear acceleration (PLA) and peak rotational acceleration (PRA) were recorded for head impacts. Athlete positions were recorded by research staff at the occurrence of each head impact. Head impacts were sustained by athletes in offensive positions more frequently than in defensive and transition positions (246, 59.9% vs. 93, 22.6% vs. 72, 17.5%). 37% of all head impacts during gameplay were sustained by athletes playing the offensive center position. Impact magnitude (means ± SD: PLA = 36.1±12.3g, PRA = 5.0±2.9 krads/sec2) did not differ between position or game scenario. Among goalies, impact frequency and magnitude were similar between games (means ± SD: 0.54±.51 hits/game, PLA = 36.9±14.2g, PRA = 4.3±4.2 krads/sec2) and practices (means ± SD: 0.96±1.11 hits/practice, PLA = 43.7±14.5g, PRA = 3.9±2.5 krads/sec2). We report that collegiate water polo athletes are at risk for sport-related head impacts and impact frequency is dependent on game scenario and player position. In contrast, magnitude does not differ between scenarios or across positions.

The Effectiveness of Protective Headgear in Attenuating Ball-to-Forehead Impacts in Water Polo.

Recent reports have demonstrated that there is a serious risk of head impact and injury in water polo. The use of protective headgear in contact sports is a commonly accepted strategy for reducing the risk of head injury, but there are few available protective headgears for use in water polo. Many of those that are available are banned by the sport's governing bodies due to a lack of published data supporting the effectiveness of those headgears in reducing head impact kinematics. To address this gap in knowledge, we launched a water polo ball at the forehead of an anthropomorphic testing device fitted with either a standard water polo headgear or one of two protective headgears. We selected a range of launch speeds representative of those observed across various athlete ages. Mixed-model ANOVAs revealed that, relative to standard headgear, protective headgears reduced peak linear acceleration (by 10.8-21.6%; p < 0.001), and peak rotational acceleration (by 24.5-48.5%; p < 0.001) induced by the simulated ball-to-forehead impacts. We discuss the possibility of using protective headgears in water polo to attenuate head impact kinematics.

Acute Exercise Effects among Young Adults with Analogue Generalized Anxiety Disorder.

Recent findings support positive effects of acute aerobic exercise on worry, state anxiety, and feelings of energy and fatigue among young adult women with subclinical, or analogue, generalized anxiety disorder (GAD). However, exercise effects among young adult men with analogue GAD are unstudied. PURPOSE: This study replicated initial findings of positive effects of acute vigorous-intensity aerobic exercise on worry, state anxiety, and feelings of energy and fatigue among young adult women with analogue GAD, examined responses among young adult men with analogue GAD, and explored sex-related differences and moderation by physical activity level, trait anxiety, depression, and poor sleep status. METHODS: Thirty-five young adults (21.4 ± 2.3 yr; 19 males; 16 females) with Penn State Worry Questionnaire scores ≥45 (60 ± 8) completed two counterbalanced 30-min conditions: treadmill running at ~71.2% ± 0.04% HR reserve and seated quiet rest. Outcomes included worry, worry engagement, absence of worry, state anxiety, and feelings of energy and fatigue. RESULTS: No outcome or moderator differed at baseline between sexes. Exercise significantly improved state anxiety (P < 0.04; d = 0.27) and feelings of energy (P < 0.001; d = 1.09). Small nonsignificant improvements were found for worry (d = 0.22), worry engagement (d = 0.18), and feelings of fatigue (d = 0.21). The magnitude of improvements in worry, worry engagement, absence of worry, and feelings of energy were stronger among females. Significant large, potentially clinically meaningful increases in feelings of energy were found among women (d = 1.35) and men (d = 0.92). A nonsignificant, but potentially clinically meaningful, moderate reduction in worry (d = 0.53) was found among women. High-trait anxiety and poor sleep quality were supported as moderators. CONCLUSIONS: Findings replicated positive effects of acute aerobic exercise among young adult women with analogue GAD, and extended to support for positive effects among young adult men with analogue GAD.

Sleep quality moderates the association between physical activity frequency and feelings of energy and fatigue in adolescents.

Physical activity (PA) can improve sleep quality, low energy, and fatigue. Though poor sleep quality may induce feelings of low energy and fatigue, the potential moderating effect of sleep quality on associations between PA and feelings of energy and fatigue among adolescents is unknown. Thus, this study examined the moderating effect of sleep quality on associations between PA frequency and feelings of energy and fatigue among adolescents in Ireland. Adolescents (N = 481; 281 males, 200 females) aged 15.1 ± 1.7 years self-reported PA frequency, feelings of energy and fatigue, and sleep quality (September to December 2015). Two-way ANCOVAs examined variation in feelings of energy and fatigue according to the interaction of PA and sleep quality. Standardized mean difference (d) quantified the magnitude of differences. Poor sleepers with low PA reported greater feelings of fatigue compared to normal sleepers with low PA (d = 1.02; 95% CI 0.60, 1.44), and poor sleepers with moderate PA reported greater feelings of fatigue compared to normal sleepers with moderate PA (d = 0.50; 0.17, 0.82). Poor sleepers with low PA reported greater feelings of fatigue compared to both poor sleepers with moderate PA (d = 0.44; 0.05, 0.83) and poor sleepers with high PA (d = 0.87; 0.46, 1.28). Poor sleepers with moderate PA reported greater feelings of fatigue compared to poor sleepers with high PA (d = 0.52; 0.14, 0.91). Poor sleep did not moderate the association between PA and feelings of energy. Sleep quality moderates the association between PA frequency and feelings of fatigue. Fatigue symptoms improve as PA frequency increases among adolescents with poor sleep quality.

Yoga Aids Blood Pressure Recovery After Exposure of Forehead to Cold: A Pilot Study.

Context: Hypotension that occurs after a single bout of aerobic exercise also attenuates the vascular response to discrete stressors, an effect that can last for hours. It is unknown whether the hypotensive benefits of traditional exercise extend to alternative forms of mindful exercise, such as yoga, to confer transient protection against neurovascular challenges that increase blood pressure (BP). Objectives: The study intended to examine the effects of acute exercise on neurovascular responses to exposure of the forehead of female yoga practitioners to vasoconstrictive cold (ie, to cold pressor stress). Design: The research team designed a study with 3 conditions (ie, with participants' participation in 3 activities on separate days in a repeated-measures design). Participants were randomly assigned to perform the activities in 1 of 3 orders across successive visits. Participants: Participants were 9 females, 20 to 33 y old, who had regularly practiced Hatha yoga from 6 mo to 12 y before the start of the study. All participants were normotensive at entry to the study and had normal body weights for their heights. Interventions: All participants performed 3 activities: (1) self-directed yoga practice, the intervention; (2) cycling exercise at a self-selected intensity, a positive control; and (3) quiet rest, a negative control. Outcome Measures: Postintervention, participants' foreheads were exposed to cold. Their systolic blood pressures (SBPs), diastolic blood pressures (DBPs), pulse rates, and forearm oxygenation were assessed using near-infrared spectroscopy. Results: Participants' SBPs and DBPs increased during cold pressor stress under all conditions, concurrent with decreased forearm oxygenation. During recovery from the cold, participants' BPs declined to near precold pressor baseline levels after yoga and cycling but remained elevated after quiet rest. Conclusions: The enhanced recovery of BP from cold applied to the forehead after yoga practice or cycling exercise suggests that both types of exercise promote a hypotensive response, which could indicate lowered cardiovascular risk.

Effects of Sprint Interval Cycling on Fatigue, Energy, and Cerebral Oxygenation.

INTRODUCTION: Feelings of fatigue are reduced after a session of continuous exercise of low-to-moderate intensity lasting 20 min or more, but only when feelings of energy are increased. Feelings of fatigue and energy have not been described after fatiguing, high-intensity interval exercise. Cerebral oxygenation has been implicated as a central correlate of fatigability, but it has not been studied concurrent with perceived fatigue during or after exercise. METHODS: Fifteen recreationally active participants (8 women, 7 men) completed bouts of sprint interval cycling (four, 30-s all-out sprints each followed by 4 min of active recovery) and a time- and work-matched bout of constant resistance cycling. Oxygenation (oxygenated hemoglobin [HbO2]) and deoxygenation (deoxygenated hemoglobin [HHb]) in the dorsolateral prefrontal cortex were measured using near-infrared spectroscopy. Fatigue ratings during each sprint and feelings of fatigue and energy during recovery were assessed. RESULTS: Increases in HbO2 and HHb in frontal cortex were greater during sprint cycling than during constant resistance cycling (P = 0.001). Fatigability (decreased power output) increased over successive sprints (P = 0.001). About 95% of the increase in fatigue ratings across sprints (P < 0.001) was accounted for by fatigability and cortical HbO2. Feelings of fatigue were decreased (P < 0.001) and feelings of energy were increased (P < 0.05) across sprint recovery periods but were unchanged during constant resistance cycling. About 85% of the changes in feelings of fatigue or energy during recovery were explained by fatigue ratings across sprints and maximum HbO2 in the cortex during recovery. CONCLUSION: Repeated, high-intensity sprints were fatiguing, but paradoxical reductions in feelings of fatigue and increases in feelings of energy occurred during recovery that were accounted for by ratings of fatigue during exercise and oxygenation in the dorsolateral prefrontal cortex during recovery.

Striatal enkephalinergic differences in rats selectively bred for intrinsic running capacity.

UNLABELLED: Rats selectively bred for high- and low-capacity for running on a treadmill (HCR; LCR) also differ in wheel-running behavior, but whether wheel-running can be explained by intrinsic or adaptive brain mechanisms is not as yet understood. It is established that motivation of locomotory behavior is driven by dopaminergic transmission in mesolimbic and mesostriatal systems. However, whether voluntary wheel running is associated with enkephalinergic activity in the ventral striatum is not known. MATERIALS AND METHODS: 40 male (20 HCR and 20 LCR) and 40 female (20 HCR and 20 LCR) rats were randomly assigned to 3 weeks of activity wheel exposure or sedentary conditions without wheel access. After 3 weeks of activity-wheel running, rats were decapitated and brains were extracted. Coronal sections were analyzed utilizing in situ hybridization histochemistry for enkephalin (ENK) mRNA in the ventral striatum. RESULTS: HCR rats expressed less ENK than LCR rats in the nucleus accumbens among females (p<0.01) and in the olfactory tubercle among both females (p<0.05) and males (p<0.05). There was no effect of wheel running on ENK mRNA expression. CONCLUSION: Line differences in ENK expression in the olfactory tubercle, and possibly the nucleus accumbens, partly explain divergent wheel-running behavior. The lower striatal ENK in the HCR line is consistent with enhanced dopaminergic tone, which may explain the increased motivation for wheel running observed in the HCR line.

Refeeding after acute food restriction: differential reduction in preference for ethanol and ethanol-paired flavors in selectively bred rats.

Rats' voluntary ethanol intake varies with dispositional factors and energy status. The joint influences of these were of interest here. We previously reported that rats selectively bred for high voluntary saccharin intake (HiS) consume more ethanol and express more robust conditioning of preference for flavors paired with voluntarily consumed ethanol than do low-saccharin consuming counterparts (LoS). Three new experiments examined the effect of refeeding after an episode of food restriction on ethanol intake and on preference for ethanol-paired flavors in HiS and LoS rats. A 48-h episode of food restriction with wheel running reduced intake of and preference for 4% ethanol (Exp. 1a) and preference for an ethanol-paired flavor (Exp. 1b) during refeeding. Food restriction alone was sufficient to reduce the flavor preference (Exp. 2). Adding fat to the refeeding diet or extending the food restriction period exacerbated the effect (Exp. 3), yielding a frank aversion to ethanol-paired flavors in LoS rats. These studies indicate that rebound from negative energy balance shifts responses to ethanol-associated cues from preference toward aversion. Analyses of bodyweight changes and caloric intake during refeeding support this conclusion and further suggest that lower metabolic efficiency may be a marker for enhanced preference mutability.