S. Lee Hong - Academia.edu (original) (raw)

Papers by S. Lee Hong

Random number generators (RNGs) are the foundation of strong security and privacy measures. With ... more Random number generators (RNGs) are the foundation of strong security and privacy measures. With an increasing number of smart devices being connected to the Internet, the demand for secure communication will only increase. An important outgrowth of Internet-connected devices is the embedding of sensors. Yet, there remains a paucity of good protocols to provide sensor-based secure RNG seeds. In their raw form, sensor data are a weak source of RNG seeds for two reasons: 1) adversarial control - a malicious party gaining control of the sensor and generating a known data sequence and 2) collinearity across sensors - inherent correlated sequences generated because sensors are embedded in the same device. We propose a new seeding technique that leverages sensor data to provide secure seeds for RNG. Given the current proliferation of sensors and Internet-connectivity on smart devices, this technique could increase cybersecurity in a variety of domains, without additional cost.

The journals of gerontology. Series A, Biological sciences and medical sciences, 2013

The goal of this study was to test whether the “loss of the complexity” hypothesis can be applied... more 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.

Current opinion in clinical nutrition and metabolic care, 2013

Age-related muscle weakness causes a staggering economic, public, and personal burden. Most resea... more 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.

Almost unequivocally, aging and neurodegeneration lead to deficits in neural information processi... more 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. Biological sources of inflexibility in brain and behavior with aging and neurodegenerative diseases. Front. Syst. Neurosci. 6:77.

Background: In Huntington's disease (HD), motor symptoms develop prior to the widespread loss of ... more Background: In Huntington's disease (HD), motor symptoms develop prior to the widespread loss of neurons in striatum and cerebral cortex. The aim of this study was to examine dysfunctional patterns of corticostriatal communication during spontaneously occurring behaviors in a transgenic mouse model of HD.

This paper seeks to present a new perspective on the aging brain. Here, we make connections betwe... more This paper seeks to present a new perspective on the aging brain. Here, we make connections between two key phenomena of brain aging: 1) increased neural noise or random background activity; and 2) slowing of brain activity. Our perspective proposes the possibility that the slowing of neural processing due to decreasing nerve conduction velocities leads to a compensatory speeding of neuron firing rates. These increased firing rates lead to a broader distribution of power in the frequency spectrum of neural oscillations, which we propose, can just as easily be interpreted as neural noise. Compensatory speeding of neural activity, as we present, is constrained by the: A) availability of metabolic energy sources; and B) competition for frequency bandwidth needed for neural communication. We propose that these constraints lead to the eventual inability to compensate for age-related declines in neural function that are manifested clinically as deficits in cognition, affect, and motor behavior.

Motor dysfunction is a consistently reported but understudied aspect of schizophrenia. Postural s... more Motor dysfunction is a consistently reported but understudied aspect of schizophrenia. Postural sway area was examined in individuals with schizophrenia under four conditions with different amounts of visual and proprioceptive feedback: eyes open or closed and feet together or shoulder width apart. The nonlinear complexity of postural sway was assessed by detrended fluctuation analysis (DFA). The schizophrenia group (n = 27) exhibited greater sway area compared to controls (n = 37). Participants with schizophrenia showed increased sway area following the removal of visual input, while this pattern was absent in controls. Examination of DFA revealed decreased complexity of postural sway and abnormal changes in complexity upon removal of visual input in individuals with schizophrenia. Additionally, less complex postural sway was associated with increased symptom severity in participants with schizophrenia. Given the critical involvement of the cerebellum and related circuits in postural stability and sensorimotor integration, these results are consistent with growing evidence of motor, cerebellar, and sensory integration dysfunction in the disorder, and with theoretical models that implicate cerebellar deficits and more general disconnection of function in schizophrenia.

Motor control, Jan 1, 2007

This experiment examined the magnitude and structure of force variability in isometric index fing... more This experiment examined the magnitude and structure of force variability in isometric index finger force production tasks at 5, 15, 25, 35, 45, 55, 65, 75, 85, and 95% of maximal force in two different finger orientations. In the finger flexion task, the participants generated a downward isometric force through index finger flexion. In the finger abduction task, isometric force was generated by adducting the index finger (mediolateral motion of the middle finger and forearm were restricted). The task-related, normal force (Fz) and tangential forces (Fx and Fy) were collected with a three-dimensional force transducer. The standard deviation (SD) of the task-related force output (Fz) increased exponentially with force level. With increasing force level, approximate entropy (ApEn, a measure of irregularity) of Fz followed an inverted-U function for finger flexion, but decreased linearly in finger abduction. However, changes in the ApEn of the tangential forces were generally opposite to that of Fz, revealing compensations in the irregularity of force output between force dimensions. The findings provide evidence that force variability is related to muscle force-length characteristics (Feldman, 1966; Gottlieb %%% Agarwal, 1988).

Motor control, Jan 1, 2012

The user has requested enhancement of the downloaded file.

Nonlinear Dynamics, Psychology, and Life Sciences, Jan 1, 2010

The entropy conservation framework describes the task-organism-environment system as a system whe... more 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.

Nonlinear dynamics, psychology, and life sciences, Jan 1, 2007

The paper addresses the process of human physiological development and aging from the perspective... more 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.

Communicative & Integrative …, Jan 1, 2012

This paper expands on recent findings that link dynamic patterns of striatal activity with patter... more This paper expands on recent findings that link dynamic patterns of striatal activity with patterns of movement and exploration in wild-type and transgenic mice (R6/2) that model Huntington's disease (HD), a fatally inherited neurological condition. Here, with HD as a backdrop, we further develop the concept of entropy conservation in brain and behavior. In particular, we propose that entropy conservation could serve as a rule that guides the process of redistributing brain activity dynamics in order to alter behavior, allowing the adaptation to an ever-changing external environment. This concept is further linked to recent neuroimaging studies in human aging, building a new bridge between our recent findings of entropy conservation and the extant literature.

Background Huntington's disease (HD) is an inherited condition that results in neurodegenerat... more Background

Huntington's disease (HD) is an inherited condition that results in neurodegeneration of the striatum, the forebrain structure that processes cortical information for behavioral output. In the R6/2 transgenic mouse model of HD, striatal neurons exhibit aberrant firing patterns that are coupled with reduced flexibility in the motor system. The aim of this study was to test the patterns of unpredictability in brain and behavior in wild-type (WT) and R6/2 mice.

Methodology/Principal Findings

Striatal local field potentials (LFP) were recorded from 18 WT and 17 R6/2 mice (aged 8–11 weeks) while the mice were exploring a plus-shaped maze. We targeted LFP activity for up to 2 s before and 2 s after each choice-point entry. Approximate Entropy (ApEn) was calculated for LFPs and Shannon Entropy was used to measure the probability of arm choice, as well as the likelihood of making consecutive 90-degree turns in the maze. We found that although the total number of choice-point crossings and entropy of arm-choice probability was similar in both groups, R6/2 mice had more predictable behavioral responses (i.e., were less likely to make 90-degree turns and perform them in alternation with running straight down the same arm), while exhibiting more unpredictable striatal activity, as indicated by higher ApEn values. In both WT and R6/2 mice, however, behavioral unpredictability was negatively correlated with LFP ApEn.

Conclusions/Significance

HD results in a perseverative exploration of the environment, occurring in concert with more unpredictable brain activity. Our results support the entropy conservation hypothesis in which unpredictable behavioral patterns are coupled with more predictable brain activation patterns, suggesting that this may be a fundamental process unaffected by HD.

Neuroscience letters, Jan 1, 2009

Experimental Brain Research, Jan 1, 2011

This study was designed to investigate the effects of increasing movement frequency of a single l... more This study was designed to investigate the effects of increasing movement frequency of a single limb on the degree of similarity and coherence of the motor outflow in the non-active limb. Twelve young adults performed a series of unilateral hand-clapping tasks (horizontal and vertical in 25-s trials) while seated. Individuals began the movements at a frequency of 1 Hz for 5 s and were required to increase the movement frequency so as to reach their maximum movement frequency during the latter parts of the trial. Hand and finger kinematics and surface EMG of each arm were recorded. The results showed a progressive emergence of overflow muscle activity and involuntary motion in the non-active arm as the movement frequency of the unilateral action increased toward the upper frequency limits of voluntary movement. This ceiling occurred within the range of 6-7 Hz. Activity in the non-active limb emerged as the movement frequency requirements increased, irrespective of the direction of motion for the task (vertical, horizontal), hand used (preferred, non-preferred) or the auditory timing stimulus provided (metronome, no-metronome). The dynamics of the motor overflow in the non-active limb exhibited time-and frequency-dependent patterns similar to those of the active arm. Together, these results demonstrate that the high-frequency unilateral movements of one limb drives the emergence of motor outflow to the opposite limb with the motor output dynamics being produced across both limbs being progressively similar as movement speed increases.

Medicine & Science …, Jan 1, 2010

ABSTRACT Athletes in a number of sports are using compression as a means to improve training, per... more ABSTRACT Athletes in a number of sports are using compression as a means to improve training, performance, and recovery. However, the efficacy of and mechanisms behind the use of lower leg compression as an ergogenic aid to improve running performance is unknown. Purpose: To examine whether or not wearing moderate lower leg compression sleeves during exercise evokes changes in running economy due to altered gait mechanics. Methods: Sixteen highly trained male distance runners completed two separate running economy (RE) tests during a single session, a treatment trial of calf compression sleeves and a control trial without compression sleeves. RE was determined by measuring oxygen consumption at three constant submaximal speeds of 233, 268, and 300 m.min-1 on a motorized treadmill. Variables related to running mechanics were measured during the last 30 seconds of each four-minute stage of the RE test via wireless tri-axial 10g accelerometer devices attached to the top of each shoe. Values of ground contact time, swing time, stride time, stride frequency (SF), and stride length (SL) were determined from accelerometric output corresponding to foot strike and toe-off events obtained from a minimum of 25 consecutive steps. Statistical significance was set at P < 0.05. Results: There were no significant differences in submaximal VO2 between control and treatment trials at any of the speeds. Additionally, there was no significant difference in the slope of the lines relating submaximal VO2 and running speed between the two experimental conditions. There were no significant differences in ground contact time, swing time, stride time, stride frequency, and stride length between control and treatment conditions at any of the running speeds. However, there was a large inter-individual variability in response to compression, and three subjects exhibited large, iii consistent reductions in VO2 at each speed with compression treatment. These three subjects demonstrated the greatest decreases in SL and SF variability with compression. Conclusions: Wearing lower leg compression does not significantly change running mechanics or oxygen consumption while running at submaximal speeds. However, the individual metabolic and gait response to wearing lower leg compression varies greatly. Submitted in partial fulfillment of the requirements for the Master of Science degree in the School of Health, Physical Education and Recreation, Indiana University

Journal of personality disorders, Jan 1, 2011

Constricted affect (CA) is a cardinal negative symptom of schizophrenia-spectrum disorders. It is... more Constricted affect (CA) is a cardinal negative symptom of schizophrenia-spectrum disorders. It is unclear whether behaviorally-defined CA occurs in individuals with schizotypy-those with the personality organization reflective of schizophrenia liability. Moreover, it is unclear whether CA contributes to real world dysfunction in this population. The present study employed computerized prosodic analysis of natural speech procured during a laboratory procedure. Subjects were 89 individuals with psychometrically-defined schizotypy and 26 controls. Groups did not differ in any of the prosody measures examined here. Within the schizotypy group, increased prosodic expression was associated with positive schizotypy traits while decreased prosodic expression was associated with negative schizotypy traits. Prosodic deficits were significantly associated with reduced prosocial behaviors (e.g., talking with friends) but were not associated with subjective social satisfaction. Prosodic deficits characterize a subset of individuals with schizotypy who show a schizoid-like reduction in social behaviors without a concomitant reduction in social satisfaction.

Developmental …, Jan 1, 2009

This study examined the hypothesis that the stability of rhythmic motor patterns increases with d... more 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. ß 2009 Wiley Periodicals, Inc. Dev Psychobiol 51: 465-473, 2009.

PloS one, Jan 1, 2011

Background: Over the last two decades, various measures of entropy have been used to examine the ... more Background: Over the last two decades, various measures of entropy have been used to examine the complexity of human postural control. In general, entropy measures provide information regarding the health, stability and adaptability of the postural system that is not captured when using more traditional analytical techniques. The purpose of this study was to examine how noise, sampling frequency and time series length influence various measures of entropy when applied to human center of pressure (CoP) data, as well as in synthetic signals with known properties. Such a comparison is necessary to interpret data between and within studies that use different entropy measures, equipment, sampling frequencies or data collection durations.

Abstract 1. In this chapter, we build on our dynamical systems theoretical perspective on motor l... more Abstract 1. In this chapter, we build on our dynamical systems theoretical perspective on motor learning and development (KM Newell et al., 2001; KM Newell, Liu, & Mayer-Kress, 2003, 2005) in presenting a system identification approach to revealing the processes of learning through the determination of the characteristic time scales of performance dynamics. This approach also leads naturally to theoretical and operational distinctions in the analysis of individual and group data—a central focus of this book. Overall, the goal is ...

Random number generators (RNGs) are the foundation of strong security and privacy measures. With ... more Random number generators (RNGs) are the foundation of strong security and privacy measures. With an increasing number of smart devices being connected to the Internet, the demand for secure communication will only increase. An important outgrowth of Internet-connected devices is the embedding of sensors. Yet, there remains a paucity of good protocols to provide sensor-based secure RNG seeds. In their raw form, sensor data are a weak source of RNG seeds for two reasons: 1) adversarial control - a malicious party gaining control of the sensor and generating a known data sequence and 2) collinearity across sensors - inherent correlated sequences generated because sensors are embedded in the same device. We propose a new seeding technique that leverages sensor data to provide secure seeds for RNG. Given the current proliferation of sensors and Internet-connectivity on smart devices, this technique could increase cybersecurity in a variety of domains, without additional cost.

The journals of gerontology. Series A, Biological sciences and medical sciences, 2013

The goal of this study was to test whether the “loss of the complexity” hypothesis can be applied... more 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.

Current opinion in clinical nutrition and metabolic care, 2013

Age-related muscle weakness causes a staggering economic, public, and personal burden. Most resea... more 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.

Almost unequivocally, aging and neurodegeneration lead to deficits in neural information processi... more 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. Biological sources of inflexibility in brain and behavior with aging and neurodegenerative diseases. Front. Syst. Neurosci. 6:77.

Background: In Huntington's disease (HD), motor symptoms develop prior to the widespread loss of ... more Background: In Huntington's disease (HD), motor symptoms develop prior to the widespread loss of neurons in striatum and cerebral cortex. The aim of this study was to examine dysfunctional patterns of corticostriatal communication during spontaneously occurring behaviors in a transgenic mouse model of HD.

This paper seeks to present a new perspective on the aging brain. Here, we make connections betwe... more This paper seeks to present a new perspective on the aging brain. Here, we make connections between two key phenomena of brain aging: 1) increased neural noise or random background activity; and 2) slowing of brain activity. Our perspective proposes the possibility that the slowing of neural processing due to decreasing nerve conduction velocities leads to a compensatory speeding of neuron firing rates. These increased firing rates lead to a broader distribution of power in the frequency spectrum of neural oscillations, which we propose, can just as easily be interpreted as neural noise. Compensatory speeding of neural activity, as we present, is constrained by the: A) availability of metabolic energy sources; and B) competition for frequency bandwidth needed for neural communication. We propose that these constraints lead to the eventual inability to compensate for age-related declines in neural function that are manifested clinically as deficits in cognition, affect, and motor behavior.

Motor dysfunction is a consistently reported but understudied aspect of schizophrenia. Postural s... more Motor dysfunction is a consistently reported but understudied aspect of schizophrenia. Postural sway area was examined in individuals with schizophrenia under four conditions with different amounts of visual and proprioceptive feedback: eyes open or closed and feet together or shoulder width apart. The nonlinear complexity of postural sway was assessed by detrended fluctuation analysis (DFA). The schizophrenia group (n = 27) exhibited greater sway area compared to controls (n = 37). Participants with schizophrenia showed increased sway area following the removal of visual input, while this pattern was absent in controls. Examination of DFA revealed decreased complexity of postural sway and abnormal changes in complexity upon removal of visual input in individuals with schizophrenia. Additionally, less complex postural sway was associated with increased symptom severity in participants with schizophrenia. Given the critical involvement of the cerebellum and related circuits in postural stability and sensorimotor integration, these results are consistent with growing evidence of motor, cerebellar, and sensory integration dysfunction in the disorder, and with theoretical models that implicate cerebellar deficits and more general disconnection of function in schizophrenia.

Motor control, Jan 1, 2007

This experiment examined the magnitude and structure of force variability in isometric index fing... more This experiment examined the magnitude and structure of force variability in isometric index finger force production tasks at 5, 15, 25, 35, 45, 55, 65, 75, 85, and 95% of maximal force in two different finger orientations. In the finger flexion task, the participants generated a downward isometric force through index finger flexion. In the finger abduction task, isometric force was generated by adducting the index finger (mediolateral motion of the middle finger and forearm were restricted). The task-related, normal force (Fz) and tangential forces (Fx and Fy) were collected with a three-dimensional force transducer. The standard deviation (SD) of the task-related force output (Fz) increased exponentially with force level. With increasing force level, approximate entropy (ApEn, a measure of irregularity) of Fz followed an inverted-U function for finger flexion, but decreased linearly in finger abduction. However, changes in the ApEn of the tangential forces were generally opposite to that of Fz, revealing compensations in the irregularity of force output between force dimensions. The findings provide evidence that force variability is related to muscle force-length characteristics (Feldman, 1966; Gottlieb %%% Agarwal, 1988).

Motor control, Jan 1, 2012

The user has requested enhancement of the downloaded file.

Nonlinear Dynamics, Psychology, and Life Sciences, Jan 1, 2010

The entropy conservation framework describes the task-organism-environment system as a system whe... more 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.

Nonlinear dynamics, psychology, and life sciences, Jan 1, 2007

The paper addresses the process of human physiological development and aging from the perspective... more 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.

Communicative & Integrative …, Jan 1, 2012

This paper expands on recent findings that link dynamic patterns of striatal activity with patter... more This paper expands on recent findings that link dynamic patterns of striatal activity with patterns of movement and exploration in wild-type and transgenic mice (R6/2) that model Huntington's disease (HD), a fatally inherited neurological condition. Here, with HD as a backdrop, we further develop the concept of entropy conservation in brain and behavior. In particular, we propose that entropy conservation could serve as a rule that guides the process of redistributing brain activity dynamics in order to alter behavior, allowing the adaptation to an ever-changing external environment. This concept is further linked to recent neuroimaging studies in human aging, building a new bridge between our recent findings of entropy conservation and the extant literature.

Background Huntington's disease (HD) is an inherited condition that results in neurodegenerat... more Background

Huntington's disease (HD) is an inherited condition that results in neurodegeneration of the striatum, the forebrain structure that processes cortical information for behavioral output. In the R6/2 transgenic mouse model of HD, striatal neurons exhibit aberrant firing patterns that are coupled with reduced flexibility in the motor system. The aim of this study was to test the patterns of unpredictability in brain and behavior in wild-type (WT) and R6/2 mice.

Methodology/Principal Findings

Striatal local field potentials (LFP) were recorded from 18 WT and 17 R6/2 mice (aged 8–11 weeks) while the mice were exploring a plus-shaped maze. We targeted LFP activity for up to 2 s before and 2 s after each choice-point entry. Approximate Entropy (ApEn) was calculated for LFPs and Shannon Entropy was used to measure the probability of arm choice, as well as the likelihood of making consecutive 90-degree turns in the maze. We found that although the total number of choice-point crossings and entropy of arm-choice probability was similar in both groups, R6/2 mice had more predictable behavioral responses (i.e., were less likely to make 90-degree turns and perform them in alternation with running straight down the same arm), while exhibiting more unpredictable striatal activity, as indicated by higher ApEn values. In both WT and R6/2 mice, however, behavioral unpredictability was negatively correlated with LFP ApEn.

Conclusions/Significance

HD results in a perseverative exploration of the environment, occurring in concert with more unpredictable brain activity. Our results support the entropy conservation hypothesis in which unpredictable behavioral patterns are coupled with more predictable brain activation patterns, suggesting that this may be a fundamental process unaffected by HD.

Neuroscience letters, Jan 1, 2009

Experimental Brain Research, Jan 1, 2011

This study was designed to investigate the effects of increasing movement frequency of a single l... more This study was designed to investigate the effects of increasing movement frequency of a single limb on the degree of similarity and coherence of the motor outflow in the non-active limb. Twelve young adults performed a series of unilateral hand-clapping tasks (horizontal and vertical in 25-s trials) while seated. Individuals began the movements at a frequency of 1 Hz for 5 s and were required to increase the movement frequency so as to reach their maximum movement frequency during the latter parts of the trial. Hand and finger kinematics and surface EMG of each arm were recorded. The results showed a progressive emergence of overflow muscle activity and involuntary motion in the non-active arm as the movement frequency of the unilateral action increased toward the upper frequency limits of voluntary movement. This ceiling occurred within the range of 6-7 Hz. Activity in the non-active limb emerged as the movement frequency requirements increased, irrespective of the direction of motion for the task (vertical, horizontal), hand used (preferred, non-preferred) or the auditory timing stimulus provided (metronome, no-metronome). The dynamics of the motor overflow in the non-active limb exhibited time-and frequency-dependent patterns similar to those of the active arm. Together, these results demonstrate that the high-frequency unilateral movements of one limb drives the emergence of motor outflow to the opposite limb with the motor output dynamics being produced across both limbs being progressively similar as movement speed increases.

Medicine & Science …, Jan 1, 2010

ABSTRACT Athletes in a number of sports are using compression as a means to improve training, per... more ABSTRACT Athletes in a number of sports are using compression as a means to improve training, performance, and recovery. However, the efficacy of and mechanisms behind the use of lower leg compression as an ergogenic aid to improve running performance is unknown. Purpose: To examine whether or not wearing moderate lower leg compression sleeves during exercise evokes changes in running economy due to altered gait mechanics. Methods: Sixteen highly trained male distance runners completed two separate running economy (RE) tests during a single session, a treatment trial of calf compression sleeves and a control trial without compression sleeves. RE was determined by measuring oxygen consumption at three constant submaximal speeds of 233, 268, and 300 m.min-1 on a motorized treadmill. Variables related to running mechanics were measured during the last 30 seconds of each four-minute stage of the RE test via wireless tri-axial 10g accelerometer devices attached to the top of each shoe. Values of ground contact time, swing time, stride time, stride frequency (SF), and stride length (SL) were determined from accelerometric output corresponding to foot strike and toe-off events obtained from a minimum of 25 consecutive steps. Statistical significance was set at P < 0.05. Results: There were no significant differences in submaximal VO2 between control and treatment trials at any of the speeds. Additionally, there was no significant difference in the slope of the lines relating submaximal VO2 and running speed between the two experimental conditions. There were no significant differences in ground contact time, swing time, stride time, stride frequency, and stride length between control and treatment conditions at any of the running speeds. However, there was a large inter-individual variability in response to compression, and three subjects exhibited large, iii consistent reductions in VO2 at each speed with compression treatment. These three subjects demonstrated the greatest decreases in SL and SF variability with compression. Conclusions: Wearing lower leg compression does not significantly change running mechanics or oxygen consumption while running at submaximal speeds. However, the individual metabolic and gait response to wearing lower leg compression varies greatly. Submitted in partial fulfillment of the requirements for the Master of Science degree in the School of Health, Physical Education and Recreation, Indiana University

Journal of personality disorders, Jan 1, 2011

Constricted affect (CA) is a cardinal negative symptom of schizophrenia-spectrum disorders. It is... more Constricted affect (CA) is a cardinal negative symptom of schizophrenia-spectrum disorders. It is unclear whether behaviorally-defined CA occurs in individuals with schizotypy-those with the personality organization reflective of schizophrenia liability. Moreover, it is unclear whether CA contributes to real world dysfunction in this population. The present study employed computerized prosodic analysis of natural speech procured during a laboratory procedure. Subjects were 89 individuals with psychometrically-defined schizotypy and 26 controls. Groups did not differ in any of the prosody measures examined here. Within the schizotypy group, increased prosodic expression was associated with positive schizotypy traits while decreased prosodic expression was associated with negative schizotypy traits. Prosodic deficits were significantly associated with reduced prosocial behaviors (e.g., talking with friends) but were not associated with subjective social satisfaction. Prosodic deficits characterize a subset of individuals with schizotypy who show a schizoid-like reduction in social behaviors without a concomitant reduction in social satisfaction.

Developmental …, Jan 1, 2009

This study examined the hypothesis that the stability of rhythmic motor patterns increases with d... more 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. ß 2009 Wiley Periodicals, Inc. Dev Psychobiol 51: 465-473, 2009.

PloS one, Jan 1, 2011

Background: Over the last two decades, various measures of entropy have been used to examine the ... more Background: Over the last two decades, various measures of entropy have been used to examine the complexity of human postural control. In general, entropy measures provide information regarding the health, stability and adaptability of the postural system that is not captured when using more traditional analytical techniques. The purpose of this study was to examine how noise, sampling frequency and time series length influence various measures of entropy when applied to human center of pressure (CoP) data, as well as in synthetic signals with known properties. Such a comparison is necessary to interpret data between and within studies that use different entropy measures, equipment, sampling frequencies or data collection durations.

Abstract 1. In this chapter, we build on our dynamical systems theoretical perspective on motor l... more Abstract 1. In this chapter, we build on our dynamical systems theoretical perspective on motor learning and development (KM Newell et al., 2001; KM Newell, Liu, & Mayer-Kress, 2003, 2005) in presenting a system identification approach to revealing the processes of learning through the determination of the characteristic time scales of performance dynamics. This approach also leads naturally to theoretical and operational distinctions in the analysis of individual and group data—a central focus of this book. Overall, the goal is ...