Principal Research Scientist, NeuRA
Senior Research Fellow, NHMRC
Associate Professor, UNSW
Jane Butler (PhD) graduated in 1999 from UNSW, worked at the Miami Project to Cure Paralysis, University of Miami supported by a NHMRC post-doctoral fellowship, and has returned to Australia in 2002 to continue her research at NeuRA. She has a broad interest in the control of human motoneurones in health on disease with a focus on the control of respiration. Current studies include investigation of the behaviour of single motor units in respiratory muscles and respiratory neural control during normal breathing and in patients with respiratory disorders such as obstructive sleep apnoea, chronic obstructive pulmonary disease, and methods to improve respiratory function and health after spinal cord injury. She also studies the changes in the motor pathway that occur during normal movement and fatigue.
This basic science project aims to examine the behaviour of human motoneurones during sustained activation to reveal their mechanisms of recovery after activation. We will take the fundamental findings from this study and compare the behaviour of motoneurones innervating muscles affected by neurological injury such as spinal cord injury and stroke.
Breathing is a complex motor task that needs to be coordinated at all times while we eat, speak, exercise and even during sleep. The breathing muscles are controlled automatically from the brainstem during normal breathing but can also be controlled voluntarily from the motor cortex. The way these two drives to the breathing muscles interact is still not well understood. While there is some evidence that there are at least two independent pathways, and that integration of the pathways occurs at the spinal cord, there is some uncertainty about whether these pathways may have some interaction in the brainstem. Our current experiments are looking at voluntary and involuntary drive to the breathing muscles to try to answer this fundamental question about the neural control of breathing. In addition we are looking at the potential cortical contributions to resting breathing in respiratory disorders.
Obstructive sleep apnoea is a sleep disorder that affects more than 4% of the population and can lead to symptoms from daytime drowsiness to high blood pressure. People with sleep apnoea are often not breathing normally during sleep and may experience periods where the airway closes and they are unable to breathe. In severe sleep apnoea this can occur 50-60 times each hour. That is once each minute. The closure of the upper airway is thought to be due to a number of factors, one of which is that the neural drive to the airway muscles is insufficient in people with sleep apnoea. In our lab, we have made the first extensive recordings from the major muscle of the upper airway, genioglossus. We have shown that the neural drive to this muscle is very complex, more so than any limb muscle. At NeuRA, we have also pioneered new methods to image this muscle using fMRI and ultrasound. We are now planning to look at how changes in muscle architecture and mechanics relate to the neural drive to the muscle and whether that relationship is maintained in people with sleep apnoea.
Our recent studies of the control of breathing muscles have shown a strong link between neural drive and mechanical action of the muscle. We showed that for a number of breathing muscles, the neural drive is directed to the muscles with the best mechanical effect for breathing. We termed this link between mechanics and neural drive ‘neuromechanical matching’. It is a new principle of muscle activation that allows for metabolically efficient activation of the muscles. This basic research finding is now leading to further studies in patients with respiratory disorders where muscle mechanics have changed. Chronic obstructive pulmonary disease is one such disease, where muscle mechanics are known to change. Our new studies will look at whether these patients have “adapted” to the changed muscle mechanics or whether their muscles may be activated inefficiently.
Not only are the breathing muscles controlled automatically from the brainstem and motor cortex, but they can be activated in response to emotion, e.g. during laughing and crying. We plan to investigate the neural pathways involved in emotional breathing in healthy volunteers.
Respiratory complications are the major cause of death for people with spinal cord injuries. People with a high level spinal cord injury are 150 times more likely to die from pneumonia than the general population. This is because after high level spinal cord injury, people have a reduced ability to cough and to clear secretions from the lungs. The major group of muscles that produce a cough are the abdominal muscles. If the abdominal muscles are paralysed after spinal cord injury then the strength of the cough will be severely reduced. In our lab, we are looking at ways to improve cough in people with spinal cord injury by using surface functional electrical stimulation of the abdominal muscles. We have shown that this type of stimulation can improve cough significantly. We are now looking for ways to further improve cough through muscle training as well as ways to develop a portable stimulator that would allow independent activation of a cough.
After cervical spinal cord injury (SCI), the respiratory muscles are partly or completely paralysed. This has two major clinical consequences: a decreased ability to get air into the lungs and a decreased ability to cough and remove secretions. This results in a lifetime of recurrent respiratory tract infections (2/year/person) that often progress to pneumonia with frequent and extended hospital admissions. People with cervical SCI are 150 times more likely to die from respiratory complications than the general population, as many as 28% die within the first year after injury. For those that survive the first year, a cervical SCI has a lifetime cost of $9.5million, a large proportion of which is attributed to respiratory-related complications. A recent longitudinal study of people with cervical SCI showed that respiratory muscle weakness is associated with incidental pneumonia. Respiratory muscle weakness also causes dyspnoea (breathlessness) and sleep-disordered breathing, which is 4-10 times more prevalent in people with SCI than the able-bodied population. Therefore, there is an urgent need to identify a simple and cost-effective treatment for respiratory muscles weakness to prevent respiratory complications after SCI, improve quality of life and reduce the burden on the healthcare system.
Our primary aim is to determine definitively the effectiveness of training on respiratory muscle strength, respiratory physiology and health outcomes. To do this we will conduct a randomised controlled trial 2 times bigger than the largest previous study, of respiratory muscle resistive load training in individuals with acute and chronic cervical SCI. The project will provide critical new knowledge about the efficacy of a simple and inexpensive respiratory muscle training regime, which can be applied immediately in the hospital and community, to minimise respiratory morbidity in people with SCI. This project also provides a unique opportunity to investigate other consequential effects of long-term respiratory muscle training that have never been studied in people with SCI. These include effects on cough efficacy, sleep-disordered breathing, breathlessness, respiratory morbidity, respiratory health and neural drive to the diaphragm, as well as quality of life.
DR CLAIRE BOSWELL-RUYS Postdoctoral fellow
DR RACHEL MCBAIN Postdoctoral fellow
DR CHAMINDA LEWIS PhD student
The aim of our study was to investigate the relation between substantia nigra (SN) echomorphology and indices of motor cortex excitability. Nigral hyperechogenicity in healthy individuals is thought to represent an SN abnormality or predisposition to Parkinson's disease (PD) and its prevalence is greater in the very old. Our study involved 20 old healthy subjects (aged 72-84 years) known to have normal (n=10) or abnormal (n=10) SN echomorphology. All were in good health with no overt neurological signs. SN morphology was assessed with transcranial sonography through the pre-auricular bone window. Motor cortical excitability and intracortical inhibition were assessed with transcranial magnetic stimulation (TMS) over the first dorsal interosseus motor area. Single stimuli were delivered during relaxation and voluntary contraction and paired stimuli were delivered during relaxation. Each cortical hemisphere was analysed separately. The response to single-pulse TMS (in motor cortex ipsilateral to the target SN) did not differ between groups. However, a significant difference between groups was observed in the paired pulse paradigm (conditioning stimulus intensity: 70% resting motor threshold; interstimulus interval: 2 ms). The conditioned motor evoked potential amplitude was significantly larger ipsilateral to the hyperechogenic SN than in controls (P=0.014). Thus, healthy subjects with SN hyperechogenicity exhibit significantly less intracortical inhibition within the motor cortex than subjects with normal echomorphology. Decreased intracortical inhibition is also observed in PD patients. This study provides further evidence that SN hyperechogenicity in healthy individuals is associated with changes characteristic of PD supporting a role for this feature as a vulnerability marker or state marker for subtle nigral dopaminergic dysfunction.
Transcranial magnetic stimulation (TMS) during voluntary muscle contraction causes a period of reduced electromyographic (EMG) activity (EMG). This is attributed to cortical inhibition and is known as the 'silent period'. Silent periods were compared in inspiratory muscles following TMS during voluntary inspiratory efforts during normocapnia, hypercapnia, and hypocapnia. TMS was delivered during isometric and dynamic contractions of scalenes and parasternal intercostals at 25% maximum inspiratory pressure. Changing end-tidal CO2 did not affect the duration of the silent period nor suppression of EMG activity during the silent period. In scalenes, silent periods were shorter for dynamic compared to isometric contractions (p<0.05); but contraction type did not alter the degree of suppression of EMG during the silent period. In parasternal intercostal, no significant differences in silent period parameters occurred for the different contraction types. The lack of effect of end-tidal CO2 suggests that descending drive from the medullary respiratory centres does not independently activate the inspiratory muscles during voluntary inspiratory efforts.
Whether interlimb reflexes emerge only after a severe insult to the human spinal cord is controversial. Here the aim was to examine interlimb reflexes at rest in participants with chronic (>1 year) spinal cord injury (SCI, n = 17) and able-bodied control participants (n = 5). Cutaneous reflexes were evoked by delivering up to 30 trains of stimuli to either the superficial peroneal nerve on the dorsum of the foot or the radial nerve at the wrist (5 pulses, 300 Hz, approximately every 30 s). Participants were instructed to relax the test muscles prior to the delivery of the stimuli. Electromyographic activity was recorded bilaterally in proximal and distal arm and leg muscles. Superficial peroneal nerve stimulation evoked interlimb reflexes in ipsilateral and contralateral arm and contralateral leg muscles of SCI and control participants. Radial nerve stimulation evoked interlimb reflexes in the ipsilateral leg and contralateral arm muscles of control and SCI participants but only contralateral leg muscles of control participants. Interlimb reflexes evoked by superficial peroneal nerve stimulation were longer in latency and duration, and larger in magnitude in SCI participants. Interlimb reflex properties were similar for both SCI and control groups for radial nerve stimulation. Ascending interlimb reflexes tended to occur with a higher incidence in participants with SCI, while descending interlimb reflexes occurred with a higher incidence in able-bodied participants. However, the overall incidence of interlimb reflexes in SCI and neurologically intact participants was similar which suggests that the neural circuitry underlying these reflexes does not necessarily develop after central nervous system injury.