Neuroscientists are helping stroke survivors regain control of their bodies by using unexpected bursts of noise to boost brain function and facilitate movement.
The bang from a car backfiring or the crack of a starter’s pistol will elicit little more than a startled response from most people. For Curtin’s neuroscientists, this type of high-intensity noise forms a key part of research into how the brain controls our movements.
Dr Welber Marinovic is currently leading research funded by the Australian Research Council into how different types of sensory stimulation such as electric shocks and loud noises can produce different responses in the brain.
The research team is ultimately trying to work out which types of sensory stimuli can help people produce more vigorous movements and when they could be applied, with a view to helping stroke patients regain control of their movements.
“What I am trying to understand are the basic brain mechanisms by which unexpected sensory stimuli leads to quicker and more vigorous movements after a go-signal, which is a phenomenon called the StartReact Effect,” Dr Marinovic says.
“Past research has shown that if you deliver an acoustic stimulus during movement execution, such as contracting your index finger in conjunction with an acoustic noise like ‘shhhh’, then that suppresses activity in the motor cortex,” he explains.
“What I have shown is an acoustic noise doesn’t always inhibit the motor cortex, it can actually facilitate cortical activity if presented at the appropriate time. This is a novel finding that has helped us to further our understanding about the StartReact Effect.
“If we can better understand the StartReact Effect and the associated mechanisms in the brain, then we can experiment with different types of stimuli and tasks to help stroke survivors relearn movements.
“Right now, we are trying to figure out the basics, that is, what are the characteristics of acoustic stimuli and what are the associated brain mechanisms; otherwise using it in rehabilitation scenarios relies on guesswork.
“I have a hypothesis that the Locus Coeruleus, a small nucleus in the brainstem, is involved in the StartReact Effect, and perhaps activation of this nucleus by an unexpected sensory stimulus rapidly increases neuron activity in the motor cortex.
“I suspect that might be the main mechanism that leads to movement facilitation, but further studies are required to test this hypothesis.”
The research team is currently exposing test subjects to very short bursts of highly intense 100 decibel white-noise – noise containing many frequencies with equal intensities – to test their ability to move on cue.
“Pure tones also work, but they are perceived as less intense and therefore less effective,” Dr Marinovic says. “The secret to making the sound a more effective stimulus is to make the timing of the sound unpredictable. For instance, the unexpected sound of a car backfiring or a pistol discharging are good examples of sounds that could trigger not only strong reflexes, but also voluntary responses from stroke patients.”
The team has tested different types of actions in association with noise stimuli including finger abduction (waving a finger back and forth) and are now testing wrist flexion and extension. They next want to try coordinated movements of two or more fingers in flexion and extension, such as touching the thumb and forefinger together.
“That is a very functional action for everyday activities like holding a coffee cup and depends greatly on corticospinal connections – connections between the motor cortex and the muscles,” Dr Marinovic says.
“The StartReact Effect might depend on task functionality or the types of muscles you are trying to move, so we want to understand whether the effect is task dependent, muscle dependent or both.
“Knowing this is important because if you have a stroke patient whose limb is impaired, you can help the patient to more easily engage in rehabilitation programs if you know which muscles are more prone to the StartReact Effect and which muscles aren’t.”
The research team also want to investigate whether exposing stroke patients to noise stimuli over a prolonged period will eventually enable them to move more easily without the requirement of hearing any accessory stimulus at all.
“During one-hour-long sessions with patients I have observed patients with great difficulty in initiating movements by themselves, but when the white noise was played they could move far more easily and vigorously,” Dr Marinovic says.
“What I want to know is, if I do this over the course of a month, is the person going to be better off even without the acoustic stimulus? And can they regain movement more quickly than people not using this type of stimulus?”
