Exploring potential new treatment for autism
New research led by CAMH’s Dr. Pushpal Desarkar is zeroing in on one of the brain’s most important features – its ability to adapt to changing circumstances, referred to as brain plasticity – to answer questions that could pave the way to a treatment for autism spectrum disorder.
In a first-of-its-kind study, Dr. Desarkar is investigating if the brain has too much plasticity in people with autism, and if this excessive plasticity, or hyperplasticity, can be reversed using brain stimulation, a novel and non-invasive treatment.
“If successful, this research might lead to a treatment for autism, for which no effective treatments exist,” says Dr. Desarkar, Psychiatrist and Clinician Scientist in the Adult Neurodevelopmental Service and the Temerty Centre for Therapeutic Brain Intervention at CAMH. “Autism spectrum disorder is the most common neurodevelopmental disorder, affecting about one per cent of Canadians.”
Can the brain have too much plasticity?
“Neuroplasticity is the ability of the brain to adjust, to reorganize in response to environmental and internal stimuli,” says Dr. Desarkar. “The best example is memory – if you re-read a book, you will recall information from the first time you read it. This is a case of neuroplasticity – it leads to lasting changes in the brain, and forms the basis of memory and language.”
“Plasticity is important for health because it means we are quite adaptive,” he adds.
Earlier research suggests that the brain may have excessive plasticity in autism spectrum disorder. People with autism may experience heightened sensitivity to touch or pain, which may be examples of hyperplasticity, says Dr. Desarkar. Another example is the fact that 25 to 30 per cent of people with autism also have epilepsy.
Tracking thumb movements to observe plasticity
The first goal of Dr. Desarkar’s research is to confirm whether people with autism have greater neuroplasticity than people without the disorder. He is studying neuroplasticity in 60 adults: 30 people with high-functioning autism and 30 individuals without autism.
While the research team can’t “see” plasticity, there is an interesting way to measure it: tracking thumb movement. This well-established indicator, thumb movement potential (formally called motor-evoked potential), works by placing an electrode on the thumb. Each study participant receives two short sessions (each about a minute long) of theta burst stimulation (TBS), a type of brain stimulation that influences plasticity. TBS delivers magnetic pulses to a specified brain region – in this case, the motor cortex, the region that controls hand movements and other voluntary movements. After administering each session of TBS, the research team measures a participant’s thumb movement potential over a two-hour period. The electrode detects not only visible movements of the thumb that result from this stimulation, but movement potential that cannot be seen.
Preliminary results to date show a difference in response. In people with autism, it takes on average 90 to 120 minutes for a person’s thumb movement potential to return to its pre-stimulation level, whereas this occurs in 40 to 60 minutes in people without autism. The prolonged response to theta burst stimulation in individuals with autism suggests brain hyperplasticity is the cause.
Can we reverse excessive plasticity?
The second part of the study holds promise as the first possible treatment for autism. Researchers are assessing if another type of brain stimulation, called repetitive transcranial magnetic stimulation (rTMS), can reverse hyperplasticity in people with autism. Like theta burst stimulation, rTMS is a non-invasive type of magnetic brain stimulation. Health Canada has approved rTMS to treat cases of depression that have not responded to other treatments.
Individuals with autism are randomly assigned to receive a single session of either therapeutic rTMS or sham rTMS, which acts like a placebo as a comparison group. Following this, the research team again provides theta burst stimulation, then measures thumb movement potential. The team is aiming to confirm if response times in people with autism decline to the same levels as seen in people without autism. This would indicate that plasticity has been stabilized with rTMS.
“Our early preliminary results are encouraging,” says Dr. Desarkar. If the study confirms that hyperplasticity is present is people with autism and can be modified with rTMS, the next step would be to determine if treatment improves symptoms associated with autism. “If we can find an effective treatment, this would be transformative for the field,” says Dr. Desarkar.
This multi-year study is supported by the University of Toronto’s Faculty of Medicine Dean’s Fund, the Innovation Fund from the Alternate Funding Plan of the Academic Health Sciences Centres of Ontario, the Caskey Francis Family Award in Clinical Research and the Scottish Rite Charitable Foundation of Canada.