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The stopping of an earlier intended action is best explained in a race between a go process and a stop process (Logan & Cowan, 1984). The finish line, to which each process races, has been likened to a point of no return, specifically one that marks the onset of a final ballistic (unstoppable) process. Of note is the typical relation of reduced go probabilities and faster go latencies at shorter signal onset asynchronies (SOAs). (The SOA is the time interval between presentation of the go signal and presentation of the stop signal.) We report, in some cases, sub-maximal surface electromyograms (EMGs) at onset when trying to stop a maximal speeded action. These data indicate reduced synaptic drive to reach the motor pools as a result of earlier stopping effects and, as such, hold important implications for a theory of control. First, we interpret these data to suggest that the point of no return is phantom. Sub-maximal EMGs indicate a point in the control stream beyond which some EMG will be later observed but, importantly, they fail to mark the onset of a final ballistic process if, once breached, the same process remains subject to further effects of stopping. The alternative interpretation, however, that of a final ballistic process that receives sub-maximal input which results in sub-maximal output (i.e., EMG onset) cannot be ruled out from these data. We used the Hoffmann (H) reflex to probe further the mechanism of control for stopping a voluntary action. The H-reflex, an involuntary reflex that is taken as an index of spinal control, is relevant to the control of stopping because it is typically facilitated a short time before EMG onset. In other words, it provides a window of control within which a final ballistic process would otherwise be expected to locate. Thus, we interpret the effects of stopping on the H-reflex before EMG onset as strong evidence against a final ballistic process. Second, while the race model can explain the relation between the go probabilities, the go latencies and the SOAs, it fails to explain the sub-maximal EMG onsets that describe that same action in some cases. We submit a mechanism of excitatory-inhibitory interaction at all times up to the motor pool to explain both sets of empirical data. The viability of this theory is demonstrated using computer analyses.

Background: Isometric handgrip (IHG) exercise increases heart rate (HR) and mean arterial pressure (MAP); MAP can be sustained after exercise via post-exercise ischemia (PEI). HR and MAP responses are mediated by feed-forward cortical signals (central command, CC) and neural feedback from active muscles (exercise pressor reflex, EPR). Purpose: Differentiate between cortical regions involved with CC versus the EPR via changes in alpha (8-12Hz) and beta (13-30Hz) power using magnetoencephalography (MEG). Methods: Participants (n=11, 22 ± 2 years) completed a repeated IHG and PEI protocol at 5% (control) and 40% maximum force. Results: HR and MAP increased (p<0.04) early during IHG (CC only), while MAP increased further (p=0.03) as IHG continued (CC & EPR). The MAP response persisted during PEI (EPR, p=0.07). During IHG, alpha and beta power decreased within the contralateral sensorimotor cortex. Power increased within MEG sensors associated with the ipsilateral (IHG-alpha) and contralateral (IHG-beta and PEI-beta) insular cortex.

One of the most elusive challenges in the diagnosis and treatment of dysphagia is the reliable identification of silent aspiration (aspiration in the absence of cough). The citric acid inhalation cough challenge offers potential for aiding in identification of silent aspiration; however clinical application of this technique is currently problematic due to an absence of normative data. Therefore, this study aimed to establish a normative data set for the Citric- Acid Inhalation Cough Challenge, as administered with facemask method. 80 healthy subjects will participate in this study, constituting 2 age groups: above and below 60 years, with equal gender representation. On 3 separate trials, they will be asked to passively inhale, via a facemask, nebulised citric acid of concentrations ranging from 08M to 2.6M with placebo interspersed. ‘Natural cough thresholds’ (NCT) and ‘Suppressed Cough Thresholds’ (SCT) will be reached when subjects cough on at least 2 out of 3 trials. The majority (92.5%) of participants reached Natural Cough Threshold by 0.8M, with 68% demonstrating Suppressed Cough Threshold also at this concentration. There were no significant differences found between males and females (p<0.05) for either NCT (p=0.9885) or SCT (p=0.44). Whilst no difference was found between youngers and elders for NCT (p=0.7254), there was a significant difference for SCT (p=0.018), with youngers better able to suppress cough. Over 90% of healthy people were found to elicit cough at 0.8M, inferring that this level would be an adequate guide for use by clinicians testing for presence/absence of cough.

Silent aspiration is associated with pneumonia and mortality, and is poorly identified by traditional clinical swallowing evaluation (CSE). Currently, there is no reliable test for detecting silent aspiration during CSE. There is, however, increasing evidence for the validity of cough reflex testing (CRT) for identifying silent aspiration. This test has the potential to significantly improve clinical assessment of dysphagia. The aim of this research programme was to further investigate the validity, reliability and clinical utility of CRT for identifying patients at risk of silently aspirating. Several aspects of CRT were explored during this research programme. Two correlational studies were conducted to validate CRT for identifying silent aspiration against videofluoroscopic swallowing study (VFSS) and flexible endoscopic evaluation of swallowing (FEES). Cough reflex threshold testing was completed on 181 patients using inhaled, nebulised citric acid. Within one hour, 80 patients underwent VFSS and 101 patients underwent FEES. All tests were recorded and analysed by two researchers blind to the result of the alternate test. Significant associations between CRT result and cough response to aspiration on VFSS (p = .003) and FEES (p < .001) were identified. Sensitivity and specificity were optimised at 0.6mol/L in patients undergoing VFSS (71%, 60% respectively) and at 0.4mol/L in patients undergoing FEES (69%, 71% respectively). A concentration of 0.8mol/L had the highest odds ratio (OR) for detecting silent aspiration (8 based on VFSS, 7 based on FEES). Coughing on lower concentrations of citric acid (0.4mol/L compared with 1.2mol/L) was a better predictive measure of silent aspiration. Diminished cough strength has also been associated with aspiration and increased risk of pneumonia. Reflexive cough is our primary defensive mechanism against aspiration and a measure of reflexive cough strength therefore holds greater relevance than one of voluntary cough strength. Despite common use and clinical applicability, the reliability of subjective cough judgements has received little attention. The inter- and intra-rater reliability of subjective judgements of cough in patients following inhalation of citric acid was assessed. Forty-five speech-language therapists (SLTs) were recruited to the first study. Of these, 11 SLTs were currently using CRT in their clinical practice (experienced raters) and 34 SLTs reported no experience with CRT (inexperienced raters). Participants provided a rating of strong, weak or absent to ten video segments of cough responses elicited by inhalation of nebulised citric acid. The same video segments presented in a different sequence were re- evaluated by the same clinicians following a 15-minute break. Inter-rater reliability for experienced raters was calculated with a Fleiss’ generalised kappa of .49; intra-rater reliability was higher with a kappa of .70. Inexperienced raters showed similar reliability with kappa values for inter-rater and intra-rater reliability of .36 and .62, respectively. SLTs demonstrated only fair to moderate reliability in subjectively judging a patient’s cough response to citric acid. Experience in making cough judgements did not improve reliability significantly. In a second study, specific training in cough physiology and cough judgement was provided to 58 trained SLTs. Inter-rater reliability of subjective judgements of cough in patients following inhalation of citric acid was assessed. Participants provided a rating of present or absent, and if present then a rating of strong or weak, to ten video segments of cough responses. Inter-rater reliability for cough presence was calculated with a Fleiss’ generalised kappa of .71 and cough strength was calculated at .61. Years of clinical experience did not improve inter-rater reliability significantly. Experience in using CRT did improve inter-rater reliability. Further validity and reliability research would be beneficial for guiding clinical guidelines and training programmes. By identifying patients at risk of silent aspiration, more informed management decisions can be made that consequently lead to a reduction in preventable secondary complications such as pneumonia. The clinical utility of CRT for reducing pneumonia in acute stroke patients was assessed through a randomised, controlled trial. Three hundred and eleven patients referred for swallowing evaluation were assigned to either 1) a control group receiving standard evaluation or 2) an experimental group receiving standard evaluation with CRT. Participants in the experimental group were administered nebulised citric acid with test results contributing to clinical decisions. Outcomes for both groups were measured by pneumonia rates at three months post stroke and other clinical indices of swallowing management. Analysis of the data identified no significant differences between groups in pneumonia rate (p = .38) or mortality (p = .15). Results of CRT were shown to influence diet recommendations (p < .0001) and referrals for instrumental assessment (p <.0001). Despite differences in clinical management between groups, the end goal of reducing pneumonia in post stroke dysphagia was not achieved. Through this research, the characteristics and outcomes associated with dysphagia secondary to stroke in New Zealand were identified. Baseline characteristics of 311 patients with dysphagia following acute stroke were collected during their hospital stay and outcomes were measured at three months post stroke. Mortality rates were 16% and pneumonia rates 27%. Mean length of stay was 24 days and only 45% of patients were in their own home at three months post stroke. Pneumonia was significantly associated with mortality and increased length of stay. Only 13% of patients received referral for instrumental assessment of swallowing. These data are discussed in reference to the National Acute Stroke Services Audit 2009 and internationally published data. The outcomes for stroke patients with dysphagia in New Zealand are poor with a high risk of pneumonia and long hospital stays when compared internationally. In summary, this research programme has contributed to our understanding of the use of CRT in patients with dysphagia. The addition of a measure of reflexive cough strength may add to clinical assessment but specific training is required to reach adequate reliability. CRT results are significantly associated with aspiration response on instrumental assessment and lower concentrations of citric acid provide a better predictive measure of silent aspiration. CRT can be standardised and therefore is not as susceptible to interpretative variance that plagues much of CSE. Sensitivity and specificity values using this CRT methodology are adequate for CRT to be incorporated into clinical protocols. Inclusion of CRT alone was not shown to be sufficient to change clinical outcomes however integration of CRT into clinical pathways may prove more successful. Further research evaluating the addition of CRT to a comprehensive CSE would add greatly to the field of dysphagia assessment.

Introduction: Elderly females are predominantly left impaired by the degenerative impact which osteoarthritis has on the 1st CMC joint. Research supports the successful implementation of early stage conservative management. Aim: To determine the viability of performing a full scale study to investigate the influence of an abductor pollicis longus strengthening program on the symptoms experienced by elderly females presenting with early stage osteoarthritis of the 1st CMC joint. Objectives: Validating data gathering instruments; evaluating methods and procedures used for recruiting, randomization; retaining, assessing and facilitating compliance of participants. Evaluation of the data capturing process. Required resources and sample size for a scientifically valid full scale study was estimated. Method: The pilot study made use of the quantitative research design proposed for a full scale study. Tools such as cost sheets and compliance logbooks were implemented along with qualitative components such as feedback questionnaires and field notes. Three retirement homes participated; 25 residents qualified to participate of which 15 were allocated to the experimental group and 10 to the control group. The experimental group participated in an 8 week exercise program; while the control group received an assistive device. Both the experimental and control groups were assessed at baseline; four weeks and after eight weeks. The assessment battery included the Kapandji index for thumb opposition, voluntary isometric total grip, 2-point pincer, 3-point pincer and key grasp strength, Visual Analogue Scale for pain and the Michigan Hand Outcome Questionnaire (MHQ). Data analysis: Data was captured by the researcher; the MHQ and feedback questionaires were independantly completed by the partiticpants. Data cleansing was conducted manually where corectness was verified by a third uninvolved party. Quantitative data was summarized and tested with the vi Generalized Estimating Equations (GEE) to detect possible changes over time. Inferential analysis and comparisons of results for the experimental and control groups could not be made. The researcher detected themes and subthemes within the qualitative data. Results/Discussion: Recruitment techniques’ response rate did not exceed 27%; qualitative data sets identified influencing factors An inclusion age of 60 years and older were suggested and to extend the research to various ethic groups. A large enough sample group for randomization was not obtained. Recommended adjustments to the assessment battery: using an adjusted MHQ as the full MHQ includes unapplicable questions; using a Numerical Rating Scale (NRS) for pain potentially being more user friendly for an elderly population; and an additional abduction active range of motion goniometer assessment for the thumb is recommended as the Kapandji scale for opposition provided limited information concerning the range of motion of the 1st CMC joint. The calculated cost per participant was R1921.60 for the control group and R3179.79 for the experimental group. Human resources were calculated at 64.2% of the entire budget. Compliance was affected by poor memory and health. Population attrition rates were calculated at an average of 48%. The feedback questionaires indentified personal gain and the feeling of contributing to a research initiative as the predominant themes for retaining the target population. Conclusion:The conducted pilot study can be used to define the parameters necessary to conduct then mentioned full scale research study, as well as assist with research designs envolving a similar target population. One more pilot study is recommended prior to a full scale study addressing topics such as including diverse races; recommended additional assessment tools and intervnetion components. / Thesis (M.O.T.)-University of KwaZulu-Natal, Durban, 2014.

Similar to quadrupedal animals, there is evidence in humans of interlimb signalling during upper and lower limb muscular activation. A product of these interconnections is modulation of motor output via remote neural input. Such remote communication can take several forms; for example, movement modifies activity between upper and lower limbs (e.g. arms to legs) and between a limb pair (e.g. one leg to the other). A specific form of modulation between homologous muscles bilaterally (i.e. the corresponding motor unit pool across the spinal cord) is also seen with strength training. However, details of these motor connections are not well known. Improved understanding of remote influences on motor output and coordination patterns may be valuable in an applied motor re-training setting. Abnormal excitability within reflex pathways of lower limb musculature is common among various neurological disorders. Thus, it is of interest whether remote inputs could be exploited to help normalize dysfunctional motor output. The primary goal of this thesis was to better our understanding of neural interlimb connections; specifically, to examine modulatory responses within the ankle flexor and extensor muscles induced by remote muscular activation associated with both rhythmic arm movement and contralateral resistance training. Further, the final objective of this work was to apply these earlier observations in the context of a post-stroke rehabilitation paradigm, aimed at normalizing muscle activation patterns within the more-affected limb. Initially, this thesis examined spinal reflex excitability within functional antagonists of the lower leg, the ankle flexors and extensor muscles, and the impact of transient, rhythmic movement on these neural networks. Hoffmann (H-) reflexes were first used as a measurement probe. Rhythmic arm cycling significantly suppressed reflex amplitude in extensors, but revealed a bidirectional (i.e. either suppression or facilitation) reflex modulation in flexor muscles. Thus, differential regulation of ankle flexor and extensor H-reflex amplitudes was evidenced during rhythmic arm movement. This may stem from differences in locomotor pattern generator output to these groups as well as increased involvement of cortical drive to the flexors relative to the extensors during rhythmic movement. These results support the presence of interlimb neural coupling, such that remote motor action (arm movement) influences lumbar spinal cord excitability. Additionally, these descending signals impact ankle flexors and extensors differentially, which illustrates a method of producing facilitative modulation of ankle flexor motor responses. Second, reciprocal inhibition (RI) was used to examine regulation of excitability between these same lower limb functional antagonists during rhythmic arm movement. Arm cycling significantly increased RI in ankle extensors, but had no effect in the flexors. This extends observation of remote motor activity-induced modulation on spinal excitability to the core circuitry that comprises the interaction between functional agonist/antagonist pairs. Moreover, the asymmetry of this effect highlights differences in descending supraspinal inputs to ankle flexors vs. extensors, and may be related to functional dorsiflexion requirements during locomotion. Subsequently, this thesis explored long term plasticity of interlimb neural modulation resulting from remote motor activation in the form of resistance training. Specifically, the within limb pair ‘cross-education’ phenomenon was investigated via unilateral isometric strength training of the ankle flexors. The first of these training interventions was implemented in a cohort of neurologically intact subjects who performed five weeks of one-sided maximal isometric dorsiflexion training. H-reflex recruitment curves were used to probe for training-induced spinal plasticity within the agonist (flexor) and antagonist (extensor) muscles bilaterally. Post-intervention, dorsiflexor torque significantly increased in the trained and untrained limbs. Further, significant changes in H-reflex excitability were detected in the trained flexor (agonist) muscle and in both extensor (antagonist) muscles. These findings reveal that muscular crossed effects can be obtained in the ankle dorsiflexor muscles, and provide novel information on agonist and antagonist spinal adaptations that accompany unilateral training. They also suggest potential for application of remote motor activation (resistance training) to induce interlimb neural plasticity within a clinical context, such as improving one-sided weakness and/or motor dysfunction following neurotrauma. The final training intervention was implemented in a chronic (>6mo post-infarct) stroke clinical group who completed six weeks of maximal isometric dorsiflexion training in the less-affected leg. Voluntary isometric strength (dorsiflexion torque, muscle activation), reciprocal inhibition (RI), walking ability and clinical function were used to quantify training effects. Post-intervention, dorsiflexion torque and maximal flexor muscle activation significantly increased in both the more-affected (untrained) and less-affected (trained) legs. Further, the relation between size of RI and level of muscle activation in the more-affected flexor muscle was significantly altered by training, and the Timed Up and Go clinical test was significantly improved. Thus, significant gains in voluntary strength, muscle activation and spinal excitability on the untrained, more-affected side after stroke can be invoked through training the opposite limb. This translates into small but observable functional improvements. Taken together, the data in this thesis provide a basis for novel motor re-training approaches. Improved understanding has been gained of the similarities and differences between remote motor influences received by ankle flexor and extensor muscles in the lower leg. These observations culminate in the implementation of a novel post-stroke training paradigm, which shows that remote muscle activation, i.e. the cross-education effect, can induce strength and functional gains in the more-affected limb. / Graduate

In the healthy young, stimulation of superficial peroneal nerve (SPn) cutaneous afferents at the ankle during walking has been shown to elicit functionally relevant neural and mechanical responses that contribute to obstacle avoidance during swing and have been referred to as stumble corrective responses. However, specific age-related differences in the stumble corrective response induced by electrically evoked cutaneous stimulation have yet to be determined. As a confounding contributor to age related changes in dynamic stability during locomotion, neural and mechanical changes in the stumble corrective response may result in a decreased ability to recover from a destabilizing incident and provide key markers of neuromuscular decline. Therefore the purpose of this study was to compare age-dependent differences in responses to electrically evoked stimulation of the superficial peroneal nerve at the ankle during walking in healthy young and elderly groups. Electromyograms (EMG) of the tibialis anterior (TA), soleus (Sol), medial gastrocnemius (MG), biceps femoris (BF) and vastus lateralis (VL) were recorded along with gait kinematics including joint displacement and angular velocity at the ankle and knee as well as toe clearance relative to the walking surface. Overall, the stumble corrective response was preserved in the elderly as evident by significant responses in kinematics and muscle activity that were similar in sign and phase to those seen in the healthy young. However, the magnitude of the kinematic responses and resulting toe clearance in older adults were significantly smaller than in the young. Further, during the swing phase of unstimulated walking cycles, there were reduced knee flexion, plantarflexion and toe clearance in the elderly with corresponding differences in muscle activity. Therefore, smaller kinematic responses to stimulation, in the elderly, superimposed on a different undisturbed gait profile, resulting in reduced toe clearance, reflects early degradation of the stumble corrective response. This early degradation is likely a prodromal sign of increased fall risk. This supports the potential use of cutaneous reflexes in quantifying degradation of neuromuscular control and its contribution to fall risk. / Graduate / 0317 / 0758 / rbrodie@uvic.ca

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