For those who have suffered a stroke, damage to the brain can result in a decreased ability to walk. The traditional therapy used for the recovery of walking, body weight supported treadmill training, has significant labour requirements that limit the availability of training to the larger stroke population. Thus, the conception and application of new, effective, and efficient rehabilitation therapies is required. To approach this, an understating of the intricate neural control behind walking is needed to form the principled foundation upon which locomotor therapies are based. Due to observations that the arms and legs are connected in the nervous system during walking, and that nervous system control is the same across rhythmic tasks, arm and leg (A&L) cycling training could provide an effective means of locomotor rehabilitation. Thus, the goal of this dissertation is focused upon exploring central nervous system control and interlimb coordination during rhythmic arm and leg movement and testing the extent to which A&L cycling training improves walking after stroke. The first objective of this dissertation was to provide further evidence of central nervous system control of walking. Through a literature review in Chapter 1 and experimental evidence in Chapter 2 of common subcortical control across rhythmic locomotor tasks, evidence for the existence of central pattern generating networks in humans is given. The second objective was to explore interlimb coordination during rhythmic movement. Results presented in Chapters 3 and 4 further our understanding of specific interlimb interactions during rhythmic arm and leg tasks. The third objective was to evaluate the effects of an A&L cycling training intervention in a post-stroke population. To support this objective, it was shown in Chapter 5 that a multiple baseline design is appropriate for use in intervention studies. In Chapter 6, it was determined that A&L cycling training can be used to improve walking ability. And in Chapter 7, it was shown that training induced plasticity in interlimb reflex pathways. Overall, results in this dissertation provide further knowledge on nervous system control and arm and leg interlimb interactions during rhythmic movements and their effect on locomotor recovery following a stroke. / Graduate / 2017-10-31

Spinal cord injury (SCI) manifests signs of spasticity, plantar flexor (PF) hyperreflexia and ankle clonus, and deficits in motor function. In individuals with motor-incomplete SCI (MISCI), ankle clonus may limit independent walking function. Ankle clonus is attributed to enhanced soleus stretch reflex (SSR) excitability due to decreased supraspinal input and maladaptive reorganization of spinal reflex circuitry. We explored these questions: 1. What are the biomechanical, clinical, and neurophysiologic correlates of ankle clonus? 2. Does locomotor training improve ankle clonus and walking function? 3. Will operant conditioning-based interventions that increase tibialis anterior activation or decrease soleus reflex excitability improve ankle motor control and walking function? In Chapter 2 we compared Ankle Clonus Drop Test (Drop Test) measures with clinical and neurophysiologic measures. Drop Test measures were highly reliable and exhibited moderate to strong correlations with clinical and neurophysiologic measures. Analysis of EMG activity during clonus revealed a predominant pattern of antagonist coactivation. In Chapter 3 we investigated the effects of locomotor training on PF and quadriceps spasticity, and walking function. We assessed responsiveness of the PF reflex threshold angle, a Drop Test measure of PF spasticity. PF and quadriceps spasticity decreased after locomotor training and were moderately correlated with increased walking speed. The PF reflex threshold angle measure discriminated between individuals with and without clonus. In Chapter 4 we compared the effects of two operant-conditioning based interventions to, (1) increase TA EMG activation (TA↑) and (2) decrease SOL H-reflex amplitude during active dorsiflexion (SOL↓), on reflex modulation, ankle motor control, and walking function. Each intervention improved walking function; however, modulated the variables in unique ways. TA↑ improved deficits of strength and range of motion, and SOL↓ improved modulation of SSR and SOL/TA coactivation. In Chapter 5 we discussed implications of our conclusions: (1) Drop Test ankle clonus measures are valid, reliable, and responsive; (2) antagonist coactivation was predominant during ankle clonus; (3) in individuals with chronic MISCI, locomotor training decreased PF and quadriceps spasticity and improved walking function; and (4) an operant conditioning-based intervention to either increase TA strength or decrease SOL reflex excitability improved spinal reflex modulation and walking function.

The focus of this thesis was to study an action that humans perform regularly, namely, to hold a morsel between the teeth and split it into smaller pieces. Three different issues related to this biting behavior were addressed:  (1) the effect of redu­c­ed perio­dontal tissues on food holding and splitting behavior; (2) the behavioral conse­quences of performing different bite tasks with different functional requirements, i.e., to split a peanut half resting on a piece of chocolate or to split both the peanut and the chocolate; and (3) the reflex modulations resul­ting from such a change in the intended bite action. The main conclusions from the experi­mental studies were the following: First, perio­dontitis, an inflam­matory disease that destroys the peri­o­dontal ligaments and the embedded perio­dontal mechanoreceptors, causes significant impairments in the masticatory abili­ty: the manipulative bite forces when holding a morsel are elevated compared to a matched control population and the bite force development prior to food split is altered. These changes are likely due to a combination of reduced sensory informa­tion from the damaged ligaments and to changes in the bite stra­tegy secon­d­ary to the unstable oral situation. Second, people exploit the anatomy of jaw-closing muscles to regulate the amount of bite force that dissipates following a sudden unloading of the jaw. Such control is necessary because without mechanisms that quickly halt jaw-closing movements after sudden unloading, the impact forces when the teeth collide could otherwise damage both the teeth and related soft tissues. Splitting a piece of chocolate, for instance, regularly requires >100N of bite force and the jaws collide within 5 ms of a split. On the other hand, when biting through heterogeneous food, the bite force needs to be kept high until the whole morsel is split. The required regulation is achieved by differen­tial­ly engaging parts of the masseter muscles along the anteroposterior axis of the jaw to exploit differences between muscle portions in their bite force generating capa­ci­ty and muscle shortening velocity. Finally, the reflex evoked by suddenly unloading the jaw—apparent only after the initial bite force dissipation—is modulated according to the bite intention. That is, when the intention is to bite through food items with multiple layers, the reflex response in the jaw opening muscles following a split is small, thus minimizing the bite force reduction. In contrast, when the intention is to rapidly decrease the bite force once a split has occurred, the reflex response is high. This pattern of reflex modulation is functionally beneficial when biting through heterogeneous food in a smooth manner. The presented studies show the significance of integrating cogni­tive, physiological and anatomical aspects when attempting to understand human masticatory control.