University of Auckland PhD student Alana McCambridge’s HRC-funded research into a novel non-invasive brain stimulation technique shows promise for helping rehabilitate patients with impaired arm co-ordination and control following a stroke.
Alana, who is of Samoan and Cook Island descent on her mother’s side and Irish descent on her father’s side, received an HRC Pacific Health Research PhD Scholarship in 2012. With the help of this scholarship she, along with her supervisor Professor Winston Byblow, have been investigating the effects of transcranial direct current stimulation (tDCS) on the excitability of motor pathways from the brain to the arm.
“This technique induces a weak direct current to the brain via electrodes placed over a person’s scalp. It can promote plasticity in the brain, which may be useful for helping to rehabilitate the arm after a stroke. However, the technique is not ‘one size fits all’, so I’ve been working on ways to optimise the brain stimulation parameters to achieve the best effect for a particular individual,” says Alana.
So far Alana has carried out four studies in healthy patients to refine the technique. This has involved stimulating the primary motor cortex in the frontal lobe – a region in the brain that helps coordinate voluntary movement throughout the body.
“When tDCS is applied over the primary motor cortex, researchers tend to forget about other parts of the motor system that may also be affected by the stimulation. That is why we’ve also been looking at the effects of brain stimulation on motor pathways beyond the primary motor cortex, that help coordinate the hand and arm together, such as when we reach for a cup of tea.
“I’ve chosen to focus on the upper limb because many stroke patients have a problem with abnormal coupling of the upper and lower arm. If they try to extend their shoulder, their elbow will flex as well; this limits their ability to use their arm for every-day activities.”
As part of her studies, Alana arranged the electrodes in different patterns or montages on the participants’ scalps to see how this affected movement of the arm. Her research, published in the prestigious Journal of Neurophysiology1,2, showed for the first time that tDCS can improve selective muscle activation in the upper arm.
“We’ve found that tDCS is modulating excitability in the brain, but the effects are quite varied between individuals,” says Alana.
For her next study Alana is looking for participants 18 years or over who have had a stroke more than six months ago and have moderate to severe arm impairment. Based on her previous studies with healthy participants, she has developed a set of criteria that will help her to identify those patients who she believes will respond well to the tDCS treatment. She is particularly keen to get as many Pacific participants as possible, as Pacific people have a high and escalating rate of stroke and show the poorest functional outcomes on returning home from hospital.
This study with stroke patients, which Alana hopes to complete by October this year, will involve collaboration with researchers in the Neurology Research Unit at the Department of Medicine, Auckland City Hospital, and the Brain Research Clinic at the University of Auckland.
Alana says she is grateful for the opportunities the HRC Pacific scholarship has given her, and she would like to continue with a career in research and academia beyond her PhD.
1 McCambridge, A, Bradman L, Stinear C, Byblow W (2011). Cathodal transcranial direct current stimulation of the primary motor cortex improves selective muscle activation in the ipsilateral arm. Journal of Neurophysiology 105: 2937–2942.
2 McCambridge, A, Stinear J, Byblow W (2014). A dissociation between propriospinal facilitation and inhibition after bilateral transcranial direct current stimulation. Journal of Neurophysiology 111: 2187–2195.