A putative role for neurogenesis in neurocomputational terms: Inferences from a hippocampal model

New neurons are generated daily in the hippocampus during adult life. They are integrated into the existing neuronal circuits according to several factors such as age, physical exercise and hormonal status. At present, the role of these new neurons is debated. Computational simulations of hippocampal function allow the effects of neurogenesis to be explored, at least from a computational perspective. The present work implements a model of neurogenesis in the hippocampus with artificial neural networks, based on a standard theoretical model of biologically plausible hippocampal circuits. The performance of the model in retrieval of a variable number of patterns or memories was evaluated (episodic memory evaluation). The model increased, in a phase subsequent to initial learning, the number of granular cells by 30% relative to their initial number. In contrast to a model without neurogenesis, the retrieval of recent memories was very significantly improved, although remotes memories were only slightly affected by neurogenesis. This increase in the quality of retrieval of new memories represents a clear advantage that we attribute to the neurogenesis process. This advantage becomes more significant for higher storage loads. The model presented here suggests an important functional role of neurogenesis on learning and memory.     

Running is the neurogenic and neurotrophic stimulus in environmental enrichment

Environmental enrichment (EE) increases dentate gyrus (DG) neurogenesis and brain-derived neurotrophic factor (BDNF) levels. However, running is considered an element of EE. To dissociate effects of physical activity and enrichment on hippocampal neurogenesis and BDNF levels, young female C57Bl/6 mice were housed under control, running, enrichment, or enrichment plus running conditions, and injected with bromodeoxyuridine. Cell genesis was assessed after 12 d and differentiation was analyzed 1 mo later. In addition, locomotor activity in the open field and hippocampal mature BDNF peptide levels were measured. Open-field adaptation was improved in all groups, compared to controls, but more so with running. New cell proliferation, survival, neuron number, and neurotrophin levels were enhanced only when running was accessible. We conclude that exercise is the critical factor mediating increased BDNF levels and adult hippocampal neurogenesis.     

Lateral dominance of legs in maximal muscle power, muscular endurance, and grading ability.

The purpose of this study was to examine lateral dominance in maximal muscle power, muscular endurance, and grading ability, using isokinetic mulscular strength in knee extension and flexion. The subjects were 50 healthy male students whose ages ranged from 19 to 23 years (M height: 173.6+/-6.2 cm, M weight: 67.2+/-6.8 kg). Their dominant legs for power exertion and for functional use were based on questionnaire items selected from those used in previous studies. The angular velocities of extension and flexion for exerting maximal muscle power were 60, 180, and 300 x sec.(-1). A continuous exertion 30 times at an angular velocity of 180 sec.(-1) was used as the load for muscular endurance. For grading ability, 25%, 50% and 75% of the maximal muscle strength at angular velocities of 60 and 180 x sec.(-1) were the required values, and the difference between these values and the exerted muscular strength was evaluated. The dominant leg and nondominant leg were compared for both power exertion and functional use. There was no lateral dominance in maximal muscle power and muscular endurance. In muscular endurance, especially, some subjects showed one leg superior in power exertion and some superior in functional use. Lateral dominance was noted across maximal muscle power and muscular endurance in grading ability. The dominant leg tended to be better than the nondominant leg in functional use. However, lateral dominance was not remarkable for flexing motion and in exertion for a short time.     

Strength Training Effects on Muscle Forces and Contributions to Whole-Body Movement in Cerebral Palsy

Strength training is often prescribed for children with cerebral palsy (CP); however, links between strength gains and mobility are unclear. Nine children (age 14?±?3?years; GMFCS I-III) with spastic CP completed a 6-week strength-training program. Musculoskeletal gait simulations were generated for four children to assess training effects on muscle forces and function. There were increases in isometric joint strength, but no statistical changes in fast-as-possible walking speed or endurance after training. The walking simulations revealed changes in muscle forces and contributions to body center of mass acceleration, with greater forces from the hip muscles during walking most commonly observed. A progressive strength-training program can result in isometric and dynamic strength gains in children with CP, associated with variable mobility outcomes.     

Effects of three training types on vitality among older adults: A self-determination theory perspective

ObjectivesTo investigate effects of endurance, functional and strength training on subjective vitality in older adults. Using the self-determination theory (SDT) framework we tested the moderating effects of autonomy support and mediating effects of need satisfaction on participants’ changes in vitality.DesignParallel-groups randomized controlled trial.Methods138 older adults (M = 74.2 years, SD = 4.5) were randomized to a training group or wait-list control, with assessments at baseline, at 7 weeks (short term), and 16 weeks (long term). Mixed models provided estimates of treatment effects, with covariates for moderating effects of autonomy support and mediating effects of need satisfaction (autonomy, competence, relatedness). Inferences were based on uncertainty in standardized effect-sizes (ES) in relation to a smallest important ES of 0.20.ResultsAt short term, effects on vitality were moderate for endurance training (ES = .70, ±.44), and small for functional (ES = .54, ±.36) and strength training (ES = .21, ±.47). At long term only endurance training had a clear effect on vitality (ES = .27, ±.38). Perceived autonomy support moderated the effect of endurance training at short term (ES = .66, ±.66), and functional training at long term (ES = .23, ±.40). Change in competence mediated the effect of functional and strength training at long term, while in endurance training high perceptions of autonomy support moderated the mediation effect of competence on vitality.ConclusionsEndurance training is recommended for increasing subjective vitality in older adults. Moderating effects of autonomy support and mediating effects of need satisfaction are partially consistent with self-determination theory.     

Effects of voluntary activation on neuromuscular endurance analyzed by surface electromyography

The purpose was to examine the relation between voluntary muscle activation and neuromuscular endurance of individual subjects based on the pattern of surface electromyography (EMG). The voluntary muscle activation was estimated from the relation between voluntary force and tetanic force superimposed on the voluntary force (twitch interpolation technique). 14 male subjects (10 regular exercisers and 4 sedentary; 21-29 years old) were divided into a High Voluntary Activation group and a Low Voluntary Activation group. A significant positive correlation of .72 (p<.01) was found between maximum voluntary torque and voluntary activation. A fatigue test was conducted during isometric contractions of 60% and 20% maximum voluntary torque. The endurance time was significantly longer for the Low Voluntary Activation group than the High Voluntary Activation group. The mean power frequency of voluntary EMG obtained from the vastus lateralis muscle decreased consistently whereas the average rectified value increased. The final change of mean power frequency relative to the initial value was significantly greater in the 60% Fatigue task than in the 20% Fatigue task. For the 60% Fatigue task, the final change of mean power frequency and average rectified value relative to the initial value was significantly greater in the Low Voluntary Activation group than in the High Voluntary Activation group. These results suggest that the individual differences in voluntary activation determine the neuromuscular performance usually evaluated as maximum voluntary torque and endurance time and that the voluntary activation may depend on the daily exercise.     

Measurements of Muscular Strength,Endurance, and Recovery Over Fifteen Successive Days

Muscular output was measured in terms of strength, endurance, impulse, and recovery, with 10 Ss, 4 times per day over 15 successive days. A general index (the mean percentage of baseline performance with all measures) indicated that performance generally improved over the first 5 or 6 days, and remained relatively stable thereafter. The measures of strength were sensitive to within-day effects, whereas endurance and recovery measures were not influenced by such circadian rhythms.     

Burnout predictors among prison officers: The moderating effect of temperamental endurance

The study investigates whether work stressors, coping styles, and work-related social support predict burnout among prison officers (N = 476). It was hypothesized that coping and social support would mediate the effects of work stressors on burnout and that these effects would be moderated by temperamental endurance. Results of structural equation modeling showed that emotion-oriented coping was positively related to emotional exhaustion, and negatively to personal accomplishment. Task-oriented coping was positively related to personal accomplishment. Social support from work was negatively related to emotional exhaustion. The effects of work stressors on burnout were mediated by work-related social support and by emotion-oriented coping. Additionally, some of these mediating effects were moderated by endurance. Work-related social support was negatively related to depersonalization only among participants with strong endurance. High level of work stressors predicted high emotion-oriented coping only among individuals with weak endurance.     

Effects of familiar and unfamiliar asynchronous music on treadmill walking endurance

To assess effects of familiarity of music on treadmill endurance, 15 female undergraduates in sports science performed an incremental treadmill walking task on three separate occasions while listening to Familiar Music, Unfamiliar Music, and White Noise. A repeated-measures analysis of variance indicated that participants walked for significantly longer when accompanied by Familiar and Unfamiliar Music in comparison to White Noise (p<.01). Although participants rated Familiar Music as significantly more motivating than Unfamiliar music (p<.05), no significant differences were found between the two music conditions for treadmill endurance. Heart rates did not appear to be influenced by music during treadmill walking or on completion of the task.     

Neurogenesis decreases with age in the canine hippocampus and correlates with cognitive function

New neurons are continually produced in the adult mammalian brain from progenitor cells located in specific brain regions, including the subgranular zone (SGZ) of the dentate gyrus of the hippocampus. We hypothesized that neurogenesis occurs in the canine brain and is reduced with age. We examined neurogenesis in the hippocampus of five young and five aged animals using doublecortin (DCX) and bromodeoxyuridine (BrdU) immunostaining. The total unilateral number of new neurons in the canine SGZ and granule cell layer (GCL) was estimated using stereological techniques based upon unbiased principles of systematic uniformly random sampling. Animals received 25mg/kg of BrdU once a day for 5 days and were euthanized 9 days after the last injection. We found evidence of neurogenesis in the canine brain and that cell genesis and neurogenesis are greatly reduced in the SGZ/GCL of aged animals compared to young. We further tested the hypothesis that an antioxidant fortified food or behavioral enrichment would improve neurogenesis in the aged canine brain and neurogenesis may correlate with cognitive function. Aged animals were treated for 2.8 years and tissue was available for six that received the antioxidant food, five that received the enrichment and six receiving both treatments. There were no significant differences in the absolute number of DCX or DCX-BrdU neurons or BrdU nuclei between the treatment groups compared to control animals. The number of DCX-positive neurons and double-labeled DCX-BrdU-positive neurons, but not BrdU-positive nuclei alone, significantly correlated with performance on several cognitive tasks including spatial memory and discrimination learning. These results suggest that new neurons in the aged canine dentate gyrus may participate in modulating cognitive functions.     

Preferences for Life-Prolonging Medical Treatments and Deference to the Will of God

We defined and measured a dimension of religiosity frequently invoked in end-of-life (EOL) research—deference to God’s Will (GW)—and examined its relationship to preferences for life-prolonging treatments. In a 35-min telephone interview, 304 older men and women (60 +) were administered the 5-item GW scale, sociodemographic questions, three attitude items regarding length of life, and measures of two health indices, depression, and life-prolonging treatment preferences. The GW scale demonstrated internal consistency (Cronbach’s alpha = .94) and predictive and discriminant validity. Higher scores indicative of greater deference to GW were associated with stronger life-prolonging treatment preferences in poor-prognosis scenarios. Implications for the role of religiosity in medical decision-making are discussed.     

Effects of Interspersed Brief Problems on Students' Endurance at Completing Math Work

An alternating treatments design was used to compare the effects of baseline, interspersed brief problems, and interspersed brief problems plus token reinforcement on students' endurance while completing math worksheets. By pairing the completion of brief problems with token reinforcement, the role of problem completion as a conditioned reinforcer was examined consistent with the discrete task completion hypothesis. Four 5th grade students who were low achieving in math participated. Each day the students completed a stack of math worksheets containing 3-digit by 3-digit addition problems with or without interspersed single-digit problems for 10 min. Dependent measures included total digits correct per session and during each min of the 10 min work period (i.e., a measure of endurance). Results indicated that total digits correct per session was highest during the interspersal plus reinforcement condition followed by interspersal and then baseline for three of the four students. In addition, both interspersal conditions resulted in greater endurance than baseline. Limitations of the current study and implications for increasing students' persistence on classroom tasks are discussed.     

Selective deficit in spatial location memory in extremely low birth weight children at age six: The PETIT Study

Spatial location memory has rarely been assessed in young children due to a scarcity of developmentally appropriate tests. This study sought to compare nonverbal learning and recall in children born extremely low birth weight (ELBW; <1000 g) and less than 33 gestational weeks (GW) with term-born children at early school age using a recently developed and adapted test. We administered a modification of the Hopkins Board to 210 children at age six; 84 born ELBW (35 born < 26 GW; 49 born 26–33 GW) and 126 term-born. Six measures were obtained: naming, trials-to-criterion, errors-to-criterion, delayed item recall, delayed location recall, and percent retention. After age correction, ELBW children had worse general cognition, item naming, delayed item recall, delayed location recall, and percent retention than term-born children. Delayed item recall and percent retention performances of ELBW children remained worse after correction for general cognition. ELBW groups (< 26 GW and 26–33 GW) groups performed worse than term-born children in naming and delayed item recall with chronological age as covariate. Those born before 26 GW, but not 26–33 GW, performed worse than term-born children in delayed location recall and percent retention. Differences remained significant after controlling for gender, maternal education, and delivery type. All three groups' performance declined from final learning trial to delayed location recall, with a decline greater for less than 26 GW than term-born children. Extreme prematurity (< 26 GW) and ELBW are significant risk factors for spatial location memory deficit. The modified Hopkins Board discriminated high-risk preterm and term-born children at early school age and appears to be a useful test to measure this rarely studied cognitive capacity.     

FIELD MEASURES OF STRENGTH AND FITNESS PREDICT FIREFIGHTER PERFORMANCE ON PHYSICALLY DEMANDING TASKS

Recruits from 9 consecutive fire academy classes were assessed on a battery of strength and endurance measures at Weeks 1, 7, and 14 of training. Regression analyses using Week 1 measures indicated that strength variables were the primary predictors of performance on physically demanding firefighting tasks assessed at the completion of training. Incremental validity was obtained with the addition of aerobic capacity, which produced more accurate performance distinctions among recruits with high strength levels. Results showed predictive validity and linearity throughout the upper range of strength and endurance levels, but evidence of an increased drop-off in performance for recruits with strength levels below the male 25th percentile. Structural equation modeling, a more powerful and comprehensive approach to validation than traditional regression, provided strong support for the construct validity of general strength and endurance as predictors of firefighter performance on physically demanding fire suppression and rescue tasks.     

Cognitive reappraisal reduces perceived exertion during endurance exercise

Emotion regulation may influence psychological responses to exercise. We examined whether the emotion regulation strategies, cognitive reappraisal and distraction, influenced psychological state and prefrontal cortex oxygenation during endurance exercise. Twenty-four endurance runners ran for 90 min at 75–85% maximum heart rate in three separate sessions with no instruction or with instructions to use cognitive reappraisal or distraction. Participants rated their emotional arousal, emotional valence, and perceived exertion before, every 30 min during, and after exercise. Functional near-infrared spectroscopy quantified changes in prefrontal cortex oxygenation. Participants felt lower emotional arousal and physical exertion when instructed to utilize cognitive reappraisal than when given no emotion regulation instruction. Such responses to distraction did not differ from the other conditions. Emotion regulation strategies did not influence emotional valence or prefrontal cortex oxygenation. Participants’ analytical interpretation of the cognitive reappraisal instruction could contribute to small effect sizes and limited effects. Further research should determine contexts under which emotion regulation strategies most benefit endurance exercise experience.     

Beat the Heat: Effects of a Motivational Self-Talk Intervention on Endurance Performance

The study examined the effects of a motivational self-talk intervention on endurance cycling performance in hot conditions. Participants were 16 physically active adult men. After a baseline VO₂ peak assessment and two training sessions, participants completed a 30 min cycling trial in a hot environment (35°C, 45% relative humidity) while maintaining a steady rate of perceived exertion. Participants of the intervention group produced greater power output during the final third of the trial. Findings suggest that the self-talk strategy seems to have compromised the aversive effects of the demanding environmental conditions and provide support for the psychobiological model of endurance performance.     

The Influence of Competition on the Efficiency of an Isometric Muscle Contraction

36 male Ss from collegiate intramural athletic teams were asked to maintain 50% of their maximum voluntary contraction on an iso-metric handle as long as possible. Ss were divided into 2 groups. One group performed individually while the other group, in teams of 3 Ss each, competed for a team prize. During the session, the active muscle was continuously monitored by EMG. The introduction of the motivational factors of competition and team presence did not increase the mean endurance time, but muscle EMG activity was significantly increased when additional motivational factors were introduced. It was concluded that team presence and competition are better described as stress factors which reduce the efficiency of the muscles. The reduction of efficiency is explained both in terms of increased activity of the antagonistic muscles and an increase in S’s general arousal level.     

Quadriceps Torque,Peak Variability and Strength Endurance in Patients after Anterior Cruciate Ligament Reconstruction: Impact of Local Muscle Fatigue

Abstract

We tested if ACL-reconstructed participants show a decreased quadriceps torque, a lower muscle endurance capacity and a higher peak torque variability compared to unimpaired control participants prior to and following local muscle fatigue. Participants (n?=?19, 10 women; 25?±?5yrs.) with unilateral hamstrings autograft ACL-reconstruction and a matched unimpaired control group were recruited. Participants performed two maximal isometric voluntary force (MIVF) contractions of the knee extensors. In between, standardized local muscle fatigue was induced. ACL-reconstructed knees display a lower peak torque of the knee extensors in comparison to the contralateral limb (3.2?±?.3Nm/kg vs. 3.5?±?.3 Nm/kg). Peak torque variability and fatigue resistance were not affected by local muscle fatigue (p > .05). Participants with ACL-reconstructed knees show a persistent quadriceps muscle dysfunction. This dysfunction and lower limb side asymmetries might be risk factors for ACL re-ruptures.     

Effects of acute endurance,strength, and coordination exercise interventions on attention in adolescents: A randomized controlled study

ObjectivesThe aim of this study was to compare three different modes of an acute bout of exercise – endurance, strength, and coordination – in their effects on adolescents' attention.DesignThis was a preregistered, prospective, randomized intervention study with four groups and two distinct measurement occasions.MethodEighty adolescent students aged 15–18 years were randomized to one of three exercise intervention groups (endurance, strength, coordination) or to a non-exercise, control group. The exercise interventions lasted for 25 min. The random assignment to the study groups was stratified according to participants' age and gender. Before and after the exercise intervention, all participants completed the revised d2-test of attention. A 4 × 2 repeated measures ANOVA with contrast-coded test was used as the main analysis method.ResultsAttentional test performance increased from before to after the exercise intervention for all exercise groups, as compared with the control group. The three exercise groups improved equally and did not differ in their attentional scores after the intervention.ConclusionsAn acute bout of exercise was in general beneficial for adolescent students' attention, while the mode of the provided exercise training was not decisive. School directors and teachers are encouraged to incorporate exercise-related breaks into their school plan.