The Narrative Impact of Active Video Games on Physical Activity Among Children: A Feasibility Study.

BACKGROUND: Active video games (AVGs) capable of inducing physical activity offer an innovative approach to combating childhood obesity. Unfortunately, children's AVG game play decreases quickly, underscoring the need to identify novel methods for player engagement. Narratives have been demonstrated to influence behaviors. OBJECTIVE: The objective of this study was to test the hypothesis that a narrative would motivate increased AVG play, though a feasibility study that investigated the motivational effect of adding a previously developed narrative cutscene to an originally nonnarrative AVG, Nintendo Wii Sports Resort: Swordplay Showdown. METHODS: A total of 40 overweight and obese 8- to 11-year-olds equally divided by sex played the AVG. Half (n=20) were randomly assigned to a narrative group that watched the narrative cutscene before game play. The other half played the game without watching it. RESULTS: Children in the narrative group had significantly (P<.05) more steps per 10-second period (mean 3.2, SD 0.7) and overall (mean 523, SD 203) during game play compared with the nonnarrative group (10-second period: mean 2.7, SD 0.7; overall: mean 366, SD 172). CONCLUSIONS: The AVG with narrative induced increased physical activity. Additional research is needed to understand the mechanisms through which narrative increases physical activity during AVG game play.

Cognitive load results in motor overflow in essential tremor.

SK is an 84-year-old woman diagnosed with essential tremor (ET) but no cognitive deficits. In this experiment, we tested the effects of mental rotation (a form of additional cognitive load) during reaching behavior (with the right hand) on the tremor profile of the non-moving left hand. We observed a marked increase in tremor and its variability, as well as the "freezing" of the movement pattern as effects of the cognitive load. These findings imply cognitive-motor overlaps in patients with ET, raising the possibility that the deficits reflect the loss of a common pool of neural resources, despite the heterogeneity of the symptoms of the disorder.

Aging and muscle: a neuron's perspective.

PURPOSE OF REVIEW: Age-related muscle weakness causes a staggering economic, public, and personal burden. Most research has focused on internal muscular mechanisms as the root cause to strength loss. Here, we briefly discuss age-related impairments in the brain and peripheral nerve structures that may theoretically lead to muscle weakness in old age. RECENT FINDINGS: Neuronal atrophy in the brain is accompanied by electrical noise tied to declines in dopaminergic neurotransmission that degrades communication between neurons. Additionally, sensorimotor feedback loops that help regulate corticospinal excitability are impaired. In the periphery, there is evidence for motor unit loss, axonal atrophy, demyelination caused by oxidative damage to proteins and lipids, and modified transmission of the electrical signal through the neuromuscular junction. SUMMARY: Recent evidence clearly indicates that muscle weakness associated with aging is not entirely explained by classically postulated atrophy of muscle. In this issue, which focuses on 'Ageing: Biology and Nutrition' we will highlight new findings on how nervous system changes contribute to the aging muscle phenotype. These findings indicate that the ability to communicate neural activity to skeletal muscle is impaired with advancing age, which raises the question of whether many of these age-related neurological changes are mechanistically linked to impaired performance of human skeletal muscle. Collectively, this work suggests that future research should explore the direct link of these 'upstream' neurological adaptions and onset of muscle weakness in elders. In the long term, this new focus might lead to novel strategies to attenuate the age-related loss of muscle strength.

Paced finger-tapping abnormalities in bipolar disorder indicate timing dysfunction.

OBJECTIVES: Theoretical and empirical evidence suggests that impaired time perception and the neural circuitry contributing to internal timing mechanisms may contribute to severe psychiatric disorders, including mood disorders. The structures that are involved in subsecond timing, i.e., cerebellum and basal ganglia, have also been implicated in the pathophysiology of bipolar disorder. However, the timing of subsecond intervals has infrequently been studied in this population. METHODS: Paced finger-tapping tasks have been used to characterize internal timing processes in neuropsychiatric disorders. A total of 42 bipolar disorder patients (25 euthymic, 17 manic) and 42 age-matched healthy controls completed a finger-tapping task in which they tapped in time with a paced (500-ms intertap interval) auditory stimulus (synchronization), then continued tapping without auditory input while attempting to maintain the same pace (continuation). This procedure was followed using the dominant index finger, then with alternating thumbs. RESULTS: Bipolar disorder participants showed greater timing variability relative to controls regardless of pacing stimulus (synchronization versus continuation) or condition (dominant index finger versus alternating thumbs). Decomposition of timing variance into internal clock versus motor implementation components using the Wing-Kristofferson model showed higher clock variability in the bipolar disorder groups compared to controls, with no differences between groups on motor implementation variability. CONCLUSIONS: These findings suggest that internal timing mechanisms are disrupted in bipolar disorder patients, independent of symptom status. Increased clock variability in bipolar disorder may be related to abnormalities in cerebellar function.

The entropy conservation principle: applications in ergonomics and human factors.

The entropy conservation framework describes the task-organism-environment system as a system where entropy remains a conserved quantity that is redistributed for the purposes of motor adaptation. In this paper, potential applications for the entropy conservation framework in the areas of ergonomics and human factors are presented. First, a brief overview of the concept of entropy conservation and explore its links to the extant literature will be provided. Following which, this paper will introduce theoretically-based methods of changing the properties of the task, environment, and organism to improve worker performance and reduce the occurrence of overuse injuries. Finally, methods of adapting the workplace to the aging organism will be explored. Overall the paper will provide a view that any changes in task, organism, or environment will result in a change to the entire system.

Development of dynamic stability in children's rhythmic movement.

This study examined the hypothesis that the stability of rhythmic motor patterns increases with developmental age in children. Children aged 6 and 10 years and adults (18- to 23-year-olds) rocked back and forth at their preferred amplitude and frequency while seated on a wooden box placed atop a force platform. Participants performed the seated rocking task with their feet supported and unsupported. There was an age-related decrease in rocking frequency and variability of the rocking cycle period, while the stability of the rocking dynamics increased, as indexed by the standard deviation of the phase angle of center of pressure motion. The presence of foot support decreased the stability of the rocking dynamics and reduced cycle period variability in the children, but not the adults. The results revealed that increments of age are associated with an increase in the stability of rhythmic motor patterns even when environmental conditions are altered.

Coupling and irregularity in the aging motor system: tremor and movement.

This experiment examined the hypothesis that aging reduces the coupling between system components, resulting in a loss of complexity in behavior. Young (18-23 years), old (60-65 years), and older old (70-75 years) subjects performed rhythmical movement and postural tasks with the index finger. Irregularity of the acceleration dynamics was lower during postural tremor and movement in the old and older old subjects, an age effect that was only observed on the mediolateral axis of motion. Coupling across the axes of motion was significantly higher during rhythmic movement in the elderly but remained unaltered across the tasks in the young adults. The results show that the loss of complexity with aging can be detected even in healthy 60-65-year-olds, but demonstrates the need for postural tremor to be examined on more than a single axis of motion. Our findings suggest that reduced motor adaptability with aging results from a greater demand on task-related reorganization of the motor output.

Age-related complexity and coupling of children's sitting posture.

This study tested the hypothesis that postural complexity increases as the coupling across the axes of motion decreases as children get older. Children aged 6 and 10 years and young adults (18-23 years) were seated on a wooden box placed atop a force platform that recorded their mediolateral and anteroposterior center of pressure (COP) motion with their feet supported and unsupported. The COP path length and complexity decreased with age, and this was paralleled by an increase in relative phase entropy across the axes of sway motion. The postural sway of the younger children was dominated by slower fluctuations that were more tightly coupled across the axes of motion than the adults. The findings support the postulation that the development of children's sitting posture is characterized by increased freedom in postural coordination that realizes a more loosely coupled but adaptive postural motion with a reduced amount of sway.

Motor entropy in response to task demands and environmental information.

This experiment tested the hypothesis that human motor adaptation can be represented as the conservation of entropy across the task, organism, and environment. Healthy young individuals generated a submaximal isometric force with the index finger of their dominant hand. Subjects performed this task under different task demands (error tolerance) and environmental information (feedback frequency) conditions. In order to extend previous findings, we employ the use of approximate entropy (ApEn) to capture the temporal aspects of the variability in the isometric force and to create links to other studies of time-series in human behavior. We showed that ApEn of the force time-series, made conditional upon satisfying the task demands, decreased as the task demands were increased and the environmental information reduced. There was a compensatory interaction between task and environment on the force dynamics that could be represented by a quadratic surface, capturing 92% of the total variance. Our results show that when faced with a reduced likelihood of achieving the task goal (increased task entropy) and an environment that provides little information (increased environmental entropy), the subjects employed similar force production strategies over time, resulting in a more regular pattern.

Entropy conservation in the control of human action.

The human motor system is highly adaptable with the ability to adjust its movement patterns under constantly changing task and environmental constraints. In this paper we develop the position that the probabilistic nature of human action can be characterized by entropies at the level of the organism, task, and environment. Systematic changes in motor adaptation are characterized as task-organism and environment-organism tradeoffs in entropy. Such compensatory adaptations lead to a view of goal-directed motor control as the product of an underlying conservation of entropy across the task-organism-environment system. The conservation of entropy supports the view that context dependent adaptations in human goal-directed action are guided fundamentally by natural law and provides a novel means of examining human motor behavior.

Stance and sensory feedback influence on postural dynamics.

This study examined the effects of ice-induced plantar desensitization and the withdrawal of visual feedback on the magnitude and time-dependent structure of postural sway variability. The magnitude of variability was quantified as the area of an ellipse enclosing 95% of the center of pressure (COP) time-series during normal and tandem stances. The same time-series were also analyzed using Approximate Entropy (ApEn) and Cross-Approximate Entropy (CrossApEn) as indices of irregularity and asynchrony between the mediolateral and anteroposterior COP motions. Variability increased during tandem stance and this increase was compounded by both visual feedback withdrawal and cutaneous desensitization. Both ApEn (mediolateral and anteroposterior COP motion) and CrossApEn increased with the withdrawal of visual feedback during the tandem stance, but decreased significantly during normal stance. The results of the study demonstrate that plantar desensitization only affected the magnitude of sway variability but did not alter its time-dependent structure. Contrasting effects on the structure of postural sway variability with visual feedback withdrawal were observed during the different stances, highlighting the role of task demands in postural dynamics.

The dynamics of structural and functional complexity across the lifespan.

The paper addresses the process of human physiological development and aging from the perspective complexity at the structural level and functional levels. The goal is to present a view of the human lifespan as a continuous increase in structural complexity of the human system, resulting in increased independence of the physiological subsystems. This brings about an increase in functional complexity early in the lifespan and an eventual loss of complexity during human aging (Lipsitz & Goldberger, 1995). Different nonlinear dynamics concepts are presented as a means of providing support for this theory of human aging and development.

Early exposure to dynamic environments alters patterns of motor exploration throughout the lifespan.

We assessed early rearing conditions on aging-related changes in mouse behavior. Two isolated-housing groups, running wheel (IHRW) and empty cage (IHEC), were compared against two enriched environments, static (EEST) and dynamic (EEDY), both of which included toys and other mice. For EEDY, the location of toys and sources of food and water changed daily, but remained constant for EEST. All mice, randomly assigned to one of the four groups at ∼4 weeks of age, remained in their respective environments for 25 weeks followed by single housing in empty cages. Beginning at ∼40 weeks of age, all mice were tested at monthly intervals in a plus-shaped maze in which we measured the number of arm entries and the probability of entering a perpendicular arm. Despite making significantly more arm entries than any other group, IHEC mice also were less likely to turn into the left or right arm, a sign of motor inflexibility. Both EEDY and EEST mice showed enhanced turning relative to IHRW and IHEC groups, but only EEDY mice maintained their turning performance for up to ∼100 weeks of age. EEDY and EEST mice also were unique in showing an increase in expression of the major glutamate transporter (GLT1) in striatum, but a decrease in motor cortex, suggesting a need for further assessment of environmental manipulations on long-term changes in forebrain glutamate transmission. Our behavioral results indicate that early exposure to continually changing environments, rather than socialization or exercise alone, results in life-long changes in patterns of motor exploration.

Behavioral inflexibility and motor dedifferentiation in persons with Parkinson's disease: bilateral coordination deficits during a unimanual reaching task.

We evaluated kinematics of people with Parkinson's disease (PD) and age-matched controls during cued and uncued reaching movements. Maximum hand velocity, its variability and shoulder-to-shoulder coupling, quantified by phase locking value (PLV), were compared between PD (n=14) and Control (n=4). The PD group achieved significantly lower maximum hand velocities during the reaching movement in comparison to the Control group (p=0.05), whereas the Control group exhibited significantly greater variability (i.e., larger SDs) of maximum hand velocities across the blocks than the PD group (p=0.01). Persons with PD exhibited higher PLVs than the healthy elderly individuals when performing reaching movements with their dominant side (p=0.05), while the PLVs did not differ between groups when the movements were performed with their non-dominant hand. The present study suggests that persons with PD have a reduced ability to: (1) modulate maximum reaching velocity; and (2) alter coordination across the shoulders to different reaching actions. In persons with PD, the velocity-oriented (dominant) limb becomes slowed and less flexible, to the point that its movement dynamics are effectively similar to that of the position-oriented (non-dominant) limb.

Weaker Seniors Exhibit Motor Cortex Hypoexcitability and Impairments in Voluntary Activation.

BACKGROUND: Weakness predisposes seniors to a fourfold increase in functional limitations. The potential for age-related degradation in nervous system function to contribute to weakness and physical disability has garnered much interest of late. In this study, we tested the hypothesis that weaker seniors have impairments in voluntary (neural) activation and increased indices of GABAergic inhibition of the motor cortex, assessed using transcranial magnetic stimulation. METHODS: Young adults (N = 46; 21.2±0.5 years) and seniors (N = 42; 70.7±0.9 years) had their wrist flexion strength quantified along with voluntary activation capacity (by comparing voluntary and electrically evoked forces). Single-pulse transcranial magnetic stimulation was used to measure motor-evoked potential amplitude and silent period duration during isometric contractions at 15% and 30% of maximum strength. Paired-pulse transcranial magnetic stimulation was used to measure intracortical facilitation and short-interval and long-interval intracortical inhibition. The primary analysis compared seniors to young adults. The secondary analysis compared stronger seniors (top two tertiles) to weaker seniors (bottom tertile) based on strength relative to body weight. RESULTS: The most novel findings were that weaker seniors exhibited: (i) a 20% deficit in voluntary activation; (ii) ~20% smaller motor-evoked potentials during the 30% contraction task; and (iii) nearly twofold higher levels of long-interval intracortical inhibition under resting conditions. CONCLUSIONS: These findings indicate that weaker seniors exhibit significant impairments in voluntary activation, and that this impairment may be mechanistically associated with increased GABAergic inhibition of the motor cortex.

Rethinking energy in parkinsonian motor symptoms: a potential role for neural metabolic deficits.

Parkinson's disease (PD) is characterized as a chronic and progressive neurodegenerative disorder that results in a variety of debilitating symptoms, including bradykinesia, resting tremor, rigidity, and postural instability. Research spanning several decades has emphasized basal ganglia dysfunction, predominantly resulting from dopaminergic (DA) cell loss, as the primarily cause of the aforementioned parkinsonian features. But, why those particular features manifest themselves remains an enigma. The goal of this paper is to develop a theoretical framework that parkinsonian motor features are behavioral consequence of a long-term adaptation to their inability (inflexibility or lack of capacity) to meet energetic demands, due to neural metabolic deficits arising from mitochondrial dysfunction associated with PD. Here, we discuss neurophysiological changes that are generally associated with PD, such as selective degeneration of DA neurons in the substantia nigra pars compacta (SNc), in conjunction with metabolic and mitochondrial dysfunction. We then characterize the cardinal motor symptoms of PD, bradykinesia, resting tremor, rigidity and gait disturbance, reviewing literature to demonstrate how these motor patterns are actually energy efficient from a metabolic perspective. We will also develop three testable hypotheses: (1) neural metabolic deficits precede the increased rate of neurodegeneration and onset of behavioral symptoms in PD; (2) motor behavior of persons with PD are more sensitive to changes in metabolic/bioenergetic state; and (3) improvement of metabolic function could lead to better motor performance in persons with PD. These hypotheses are designed to introduce a novel viewpoint that can elucidate the connections between metabolic, neural and motor function in PD.

Increased metabolic flexibility and complexity in a long-lived growth hormone insensitive mouse model.

The goal of this study was to test whether the "loss of the complexity" hypothesis can be applied to compare the metabolic patterns of mouse models with known differences in metabolic and endocrine function as well as life span. Here, we compare the complexity of locomotor activity and metabolic patterns (energy expenditure, VO2, and respiratory quotient) of the long-lived growth hormone receptor gene deleted mice (GHR(-/-)) and their wild-type littermates. Using approximate entropy as a measure of complexity, we observed greater metabolic complexity, as indicated by greater irregularity in the physiological fluctuations of the GHR(-/-) mice. Further analysis of the data also revealed lower energy costs of locomotor activity and a stronger relationship between locomotor activity and respiratory quotient in the GHR(-/-) mice relative to controls. These findings suggest underlying differences in metabolic modulation in the GHR(-/-) mice revealed especially through measures of complexity of their time-dependent fluctuations.

Aging induced loss of complexity and dedifferentiation: consequences for coordination dynamics within and between brain, muscular and behavioral levels.

Growing evidence demonstrates that aging not only leads to structural and functional alterations of individual components of the neuro-musculo-skeletal system (NMSS) but also results in a systemic re-organization of interactions within and between the different levels and functional domains. Understanding the principles that drive the dynamics of these re-organizations is an important challenge for aging research. The present Hypothesis and Theory paper is a contribution in this direction. We propose that age-related declines in brain and behavior that have been characterized in the literature as dedifferentiation and the loss of complexity (LOC) are: (i) synonymous; and (ii) integrated. We argue that a causal link between the aforementioned phenomena exists, evident in the dynamic changes occurring in the aging NMSS. Through models and methods provided by a dynamical systems approach to coordination processes in complex living systems, we: (i) formalize operational hypotheses about the general principles of changes in cross-level and cross-domain interactions during aging; and (ii) develop a theory of the aging NMSS based on the combination of the frameworks of coordination dynamics (CD), dedifferentiation, and LOC. Finally, we provide operational predictions in the study of aging at neural, muscular, and behavioral levels, which lead to testable hypotheses and an experimental agenda to explore the link between CD, LOC and dedifferentiation within and between these different levels.

The effects of incidentally learned temporal and spatial predictability on response times and visual fixations during target detection and discrimination.

Responses are quicker to predictable stimuli than if the time and place of appearance is uncertain. Studies that manipulate target predictability often involve overt cues to speed up response times. However, less is known about whether individuals will exhibit faster response times when target predictability is embedded within the inter-trial relationships. The current research examined the combined effects of spatial and temporal target predictability on reaction time (RT) and allocation of overt attention in a sustained attention task. Participants responded as quickly as possible to stimuli while their RT and eye movements were measured. Target temporal and spatial predictability were manipulated by altering the number of: 1) different time intervals between a response and the next target; and 2) possible spatial locations of the target. The effects of target predictability on target detection (Experiment 1) and target discrimination (Experiment 2) were tested. For both experiments, shorter RTs as target predictability increased across both space and time were found. In addition, the influences of spatial and temporal target predictability on RT and the overt allocation of attention were task dependent; suggesting that effective orienting of attention relies on both spatial and temporal predictability. These results indicate that stimulus predictability can be increased without overt cues and detected purely through inter-trial relationships over the course of repeated stimulus presentations.

Biological sources of inflexibility in brain and behavior with aging and neurodegenerative diseases.

Almost unequivocally, aging and neurodegeneration lead to deficits in neural information processing. These declines are marked by increased neural noise that is associated with increased variability or inconsistency in behavioral patterns. While it is often viewed that these problems arise from dysregulation of dopamine (DA), a monoamine modulator, glutamate (GLU), an excitatory amino acid that interacts with DA, also plays a role in determining the level of neural noise. We review literature demonstrating that neural noise is highest at both high and low levels of DA and GLU, allowing their interaction to form a many-to-one solution map for neural noise modulation. With aging and neurodegeneration, the range over which DA and GLU can be modulated is decreased leading to inflexibility in brain activity and behavior. As the capacity to modulate neural noise is restricted, the ability to shift noise from one brain region to another is reduced, leading to greater uniformity in signal-to-noise ratios across the entire brain. A negative consequence at the level of behavior is inflexibility that reduces the ability to: (1) switch from one behavior to another; and (2) stabilize a behavioral pattern against external perturbations. In this paper, we develop a theoretical framework where inflexibility across brain and behavior, rather than inconsistency and variability is the more important problem in aging and neurodegeneration. This theoretical framework of inflexibility in aging and neurodegeneration leads to the hypotheses that: (1) dysfunction in either or both of the DA and GLU systems restricts the ability to modulate neural noise; and (2) levels of neural noise and variability in brain activation will be dedifferentiated and more evenly distributed across the brain; and (3) changes in neural noise and behavioral variability in response to different task demands and changes in the environment will be reduced.