<p>Human skeletal muscles possess thixotropic, i.e. history-dependent mechanical properties. This means that the degree of passive muscle stiffness and resting tension is dependent on the immediately preceding history of contractions and length changes. Athletes, for instance, reduce passive muscle stiffness by various types of ‘limbering-up’ procedures, whereas muscle stiffness gradually increases during inactivity.</p><p>Passive resistance of antagonistic muscles may significantly add to the total load during voluntary muscle contractions. This resistance may vary from one moment to another, depending on immediately preceding events. This research was conducted to determine whether history-dependent variations in passive muscular forces influence motor control of voluntary joint movements and steady maintenance of joint positions in healthy subjects. </p><p>In study I, the EMG signal revealed motor compensations for history-dependent variations in passive stiffness of the antagonists during slow voluntary wrist joint movements. Studies II and III demonstrated that the voluntary muscle activity required to maintain a certain wrist joint position was highly influenced by previous changes in forearm muscle length and contractions. Study IV showed that rapid voluntary movements varied in speed and onset time depending on the prevailing degree of muscle resistance, and in addition that the central nervous reaction time required to execute rapid movements was highly influenced by immediately preceding muscle-conditioning procedures.</p><p>History-dependent variations in passive muscular forces seem to be effectively compensated by the motor control system. Presumably, voluntary motor commands to the muscles are automatically adjusted in strength to history-dependent changes in passive muscular forces. Such adjustments occur within the central nervous system, which receives information about the mechanical state of the muscles. Several issues in connection with muscle thixotropy remain unaddressed. For instance, do alterations in the normal thixotropic mechanical behaviour of the muscles impose a particular problem in patients with certain neuromuscular diseases? </p>

Human skeletal muscles possess thixotropic, i.e. history-dependent mechanical properties. This means that the degree of passive muscle stiffness and resting tension is dependent on the immediately preceding history of contractions and length changes. Athletes, for instance, reduce passive muscle stiffness by various types of ‘limbering-up’ procedures, whereas muscle stiffness gradually increases during inactivity. Passive resistance of antagonistic muscles may significantly add to the total load during voluntary muscle contractions. This resistance may vary from one moment to another, depending on immediately preceding events. This research was conducted to determine whether history-dependent variations in passive muscular forces influence motor control of voluntary joint movements and steady maintenance of joint positions in healthy subjects. In study I, the EMG signal revealed motor compensations for history-dependent variations in passive stiffness of the antagonists during slow voluntary wrist joint movements. Studies II and III demonstrated that the voluntary muscle activity required to maintain a certain wrist joint position was highly influenced by previous changes in forearm muscle length and contractions. Study IV showed that rapid voluntary movements varied in speed and onset time depending on the prevailing degree of muscle resistance, and in addition that the central nervous reaction time required to execute rapid movements was highly influenced by immediately preceding muscle-conditioning procedures. History-dependent variations in passive muscular forces seem to be effectively compensated by the motor control system. Presumably, voluntary motor commands to the muscles are automatically adjusted in strength to history-dependent changes in passive muscular forces. Such adjustments occur within the central nervous system, which receives information about the mechanical state of the muscles. Several issues in connection with muscle thixotropy remain unaddressed. For instance, do alterations in the normal thixotropic mechanical behaviour of the muscles impose a particular problem in patients with certain neuromuscular diseases?

Previous studies in animals and humans show anatomic and physiological connections between the trigeminal and cervical regions. This investigation tested the hypothesis of a functional integration between the human jaw and neck motor systems in rhythmic jaw activities. By means of a wireless optoelectronic 3-D movement recording system, spatiotemporal characteristics of mandibular and head-neck movements were studied during rhythmic jaw opening-closing and chewing tasks, in healthy and in individuals with pain and dysfunction in the jaw and neck region following neck trauma, Whiplash-associated Disorders (WAD). As a basis, a methodological study evaluated the applicability of skin and teeth attached reflex markers fixed to the lower jaw and to the head in optoelectronic recording of chewing movements. The results showed concomitant and coordinated mandibular and head movements during rhythmic jaw tasks. The start of the head movement generally preceded the start of the mandibular movement. For chewing, larger size and harder texture of bolus were associated with larger head extension and larger amplitude of both mandibular and head movements. Immobilization of the head by mechanical fixation deranged jaw motor behaviour with regard to speed and amplitude of mandibular movements. Even with head fixation, muscle activity was present in neck muscles during activities. Compared to healthy subjects, WAD individuals showed smaller amplitudes and disturbed coordination of mandibular and head movements. Furthermore, a dynamic load test showed a reduced endurance during chewing in the WAD group. In conclusion, the results suggest that optimal jaw function requires free unrestricted head-neck movements and support the hypothesis of a close functional relationship between the jaw and the neck regions in rhythmic jaw activities. A new concept for human jaw function is proposed, in which "functional jaw movements" are the result of activation of jaw as well as neck muscles, leading to simultaneous movements in the temporomandibular, atlanto-occipital and cervical spine joints. The finding of an association between neck injury and disturbed jaw behaviour suggest that assessment and management of neck injured patients should include jaw function.

Pain from the musculoskeletal system is very common in the modern society. Chronic musculoskeletal pain syndromes causes not only individual suffering but also dysfunctions of movements and postural control, as large costs for the society. In spite of significant efforts, there is a shortage of knowledge on effective prevention, diagnoses and rehabilitation of different chronic musculoskeletal pain syndromes. The general aims of this thesis was to investigate the predictive value of physical, sociodemographic, and psychosocial-behavioural variables for pain reduction after multimodal rehabilitation in patients with chronic low back or neck pain, and to develop and evaluate tests for objective and quantitative evaluation of characteristic sensorimotor disturbances in chronic neck pain. Logistic regression models revealed that unchanged pain intensity could be predicted with good precision while reduced pain intensity after rehabilitation was poorly predicted by the baseline variables. Altered pain intensity in chronic low back pain was predicted by high pain intensity, low levels of pain severity and high affective distress, while reduced pain intensity for patients with chronic neck pain were predicted by high endurance, low age, high pain intensity, low need of being social along with optimistic attitudes on how the pain will interfere with daily life, and few vegetative symptoms. One of the conclusions was that objective measures of specific sensorimotor disturbances should improve the precision by which treatment-induced effects can be assessed and predicted. A study was designed to objectively and quantitatively evaluate a large numbers of different sensorimotor characteristics in a small group of patients with chronic neck pain of different aetiology (whiplash-related and insidious). Kinematic data was recorded during different motor tasks, involving cervical rotations, arm movements and standing. In comparison to a group of asymptomatic control subjects, patients with chronic neck pain was characterised by slower movements, poor balance, reduced cervical stability during perturbations, altered smoothness of movement (jerk index), and reduced movement precision (variable error and variability in range of motion). The sensorimotor variables velocity of arm movements and cervical stability, could correctly classified nearly 90% of the subjects as having chronic neck pain or being asymptomatic. There was a large diversity of sensorimotor disturbances among the individual patients. This was confirmed in a regression model that failed to separate the groups insidious neck pain (sensitivity 44%) and WAD (sensitivity 67%). By investigating associations between the different sensorimotor variables, close relations was found between the repositioning acuity and variability in range of motion, and between standing balance and cervical stability/ standing balance during perturbation. These two groups of variables were only weakly related to each other and to smoothness of movement and movement velocity. The results indicate that chronic neck pain is characterised by specific sensorimotor deficits, and that there are common pathophysiological mechanisms in chronic neck pain of different aetiology. However, the lack of associations between several sensorimotor disturbances indicates that different mechanisms are involved. The thesis indicates that objective sensorimotor tests should be used to improve the quality of functional assessments in chronic neck pain. Methods that objectively and quantitatively measure e.g. movement precision, balance and cervical stability are also needed in order to evaluate current treatment methods and to develop new rehabilitation programs for specific sensorimotor deficits.

Adaptation to changing social conditions is important for many social animals. Here, the effects of social experience on the behavior and neurophysiology of the red swamp crayfish, Procambarus clarkii, were studied. Evidence is presented that shows juvenile crayfish interact and form social order, and their behavior patterns shift in accordance to social status. Dominant animals maintain a high level of aggressive behavior, while subordinates shift their behavior pattern from aggressive to submissive behavior. Adult male crayfish show similar behavior pattern during dominance formation. However, this work demonstrates that male crayfish adopt a unique strategy to signify the formation of a social order expressed in the form of pseudocopulation. Pseudocopulation between male crayfish signifies the acceptance of the social status and leads to the reduction of aggression of dominants and enhances the survival of subordinate animals. I investigated the long-term effects of social status on the behavioral and physiological responses of crayfish to unexpected sensory touch. I discovered that animals of different social experience display different orienting responses that correlate with in vivo electromyographic recordings from the legs’ depressor muscle. The status-dependent response patterns observed in vivo are retained in a reduced, in vitro, preparation that lacks descending input from the brain. The role of serotonin (5-HT) was investigated in mediating the motor output patterns of the depressor nerve. Putative serotonergic innervations of the depressor nerve were identified that originate from serotonergic neurons located in the first abdominal ganglion. Selective stimulation of the ipsilateral 5-HT neuron enhances the response of the depressor nerve to sensory stimulation. Application of 5-HT modestly increased the tonic firing activity of the depressor nerve in social isolates and subordinates but significantly decreased the activity in dominants. This work illustrates that the formation of a dominance relationship significantly and immediately alters the behavior of the participants. As the social relationship matures, the social experience that develops affects the underlying neurophysiology that mediates the behavior. It will be of great interest in future studies to identify not only the effects rather the mechanisms of how social experience induces physiological changes.

Research has shown that maximal exercise has a significant effect on cells of the immune system. Specifically, lymphocyte count increases during exercise and decreases to a value lower than baseline following an acute exhaustive bout of exercise. The overall lymphocyte response is well characterized, however, the ability of exercise to affect lymphocyte subfractions is unknown to our knowledge. The purpose of this study was to assess and evaluate the affects of a simulated tennis match across two sessions on lymphocyte subsets. Initial measurements such as age, height, weight, skinfold analysis, and heart rate were recorded for each player, as well as blood samples being obtained by a finger prick before and after the tennis sessions. The tennis protocol started with five serves to the deuce court and five serves to the ad court, then individuals hit twenty-four forehands and twenty-four backhands against an oscillating ball machine. Each bout of serves and ground strokes were repeated ten times, with one minute rests in between each session. Before and immediately after completing the tennis trial, subjects were pricked with a lancet on the non dominant hand so to obtain at least two capillary tubes of blood. Whole blood was then added to the antibody cocktail, which is mixed according to the antibodies that were tested, which were CD4, CD8, CD19, CD95, and CX3CR1. Whole blood was added to red blood cell lysis buffer and fixation buffer, and the blood solution was incubated with antibodies specific to cell phenotype. The main results of this study indicated that there was a decrease in mainly post cell counts in pre and post CD19/CD95 measurements (P= .007), an increase in CD8/CX3CR1 in pre counts and an increase then decrease in post counts without wearing the bionic glove (P= .042), and a decrease in CD4 in the post count measurement with the bionic tennis glove (P= .043). The study’s can assist in making recommendations for after match treatment such as health and diet suggestions. Knowledge of prevention and treatment methods are low in the field of tennis and immune functions, so findings in this area could prevent elite athletes from contracting infections between matches.

This dissertation demonstrates a new method for inferring a representation of the motor command, generated by the central nervous system for interactive point-to-point movements. This new tool, the input inference neural network or IINN, allows estimation of the complexity of the motor command. The IINN was applied to experimental data gathered from 7 volunteer subjects who performed point-to-point tasks while interacting with a specially constructed haptic robot. The motor plan inference demonstrates that, for the point-to-point movement tasks executed during experiments, the motor command can be projected onto a low-dimensional manifold. This dimension is estimated to be 4 or 5 and far less than the degrees of freedom available in the arm. It is hypothesized that subjects simplify the problem of adapting to changing environments by projecting the motor control problem onto a motor manifold of low dimension. Reducing the dimension of the movement optimization problem through the development of a motor manifold can explain rapid adaptation to new motor tasks.

This dissertation demonstrates a new method for inferring a representation of the motor command, generated by the central nervous system for interactive point-to-point movements. This new tool, the input inference neural network or IINN, allows estimation of the complexity of the motor command. The IINN was applied to experimental data gathered from 7 volunteer subjects who performed point-to-point tasks while interacting with a specially constructed haptic robot. The motor plan inference demonstrates that, for the point-to-point movement tasks executed during experiments, the motor command can be projected onto a low-dimensional manifold. This dimension is estimated to be 4 or 5 and far less than the degrees of freedom available in the arm. It is hypothesized that subjects simplify the problem of adapting to changing environments by projecting the motor control problem onto a motor manifold of low dimension. Reducing the dimension of the movement optimization problem through the development of a motor manifold can explain rapid adaptation to new motor tasks.

We all have a body : our own body and just one body. Through it, we move, we interact with the world and other persons, we perceive, basically we live. It's a unique essential object. If it is true that we have only one physical body, we also have many representations of it in the brain. There is little agreement about the exact number of body representations in the brain, but not on the fact that we have more than one. The multi-componential models of body representation are based on the notion, supported by scientific evidence that different activities demand and rely on specifically adapted representations. In my thesis, I studied one particular body representation that is used and involved in action planning and execution, i.e. the Body Schema. I have been able to describe and measure the plasticity of the Body Schema and its level of specificity in healthy individuals. In particular, using a tool-use paradigm, I showed that the Body Schema is quickly and efficiently updated once a change in the body configuration occurs. With a series of kinematic studies, I contributed unveiling the ingredients that rule the plasticity of the BS and the sensory information that is used to this purpose. As a result of my thesis, I suggest that a clearer definition and operational description of the Body Schema, as an action-devoted repertoire of effectors representations, is possible, particularly thanks to its plastic features

Multiple domains of deficit have been proposed to account for the apparent reading failure of children with a reading disability. Deficits in both phonological awareness and rapid automatized naming are consistently linked with the development of a reading disability in young school age children. Less research, however, has sought to connect these two reading related processes to global theories of deficit, such as temporal processing deficits, in the explanation of reading fluency difficulties. This study sought to explore the relationship between aspects of temporal processing, as indexed through measures of motor fluency and control, and measures of reading related processes, phonological awareness and rapid automatized naming, to word reading fluency. Using structural equation modeling, measures of patterned motor movement were found to be negatively and significantly related to measures of phonological awareness. Measures of oral and repetitive movement were found to be positively and significantly related to measures of patterned movement. Finally, phonological awareness was found to be a significant predictor of word reading fluency both independently and through rapid automatized naming. No direct relationship between measures of motor control and fluency and word reading fluency was found. These findings suggest that temporal processing, as indexed by measures of motor fluency and control, are moderately predictive of the facility with which a child with a reading disability can access, manipulate, and reproduce phonetically based information. Implications for the inclusion of motor based measures in the assessment of children with reading disabilities and future directions for research are discussed.