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This article is evidence-based, verified by Ashleigh Willis, a Neuroscience Ph.D. candidate.
Our brains run on a delicate balance of excitatory and inhibitory activity. Nerve cells, or neurons, within the brain communicate via electrical and chemical signaling. Electrical signals can be contained within small networks or travel long-distances. Disruption to electrical activity within the brain can have enormous consequences. Imbalanced excitation-inhibition is a core physiological feature of many psychiatric disorders.
Scientists now understand that human behavior relies on harmonious communication between brain regions. It’s becoming clear that disrupted connectivity is at the heart of many disorders. This includes psychiatric conditions such as autism, depression, and schizophrenia.
However, altering neuronal signaling and connectivity with pharmacological methods is a tricky business. Drugs that alter neuronal signaling can result in lots of unpleasant side effects. This is because many medications have ‘off-target’ effects that disrupt other biological systems.
The exciting news is that not all biological interventions have to use pharmacology. Neuroscientists have started repurposing non-invasive experimental techniques to treat psychiatric disorders.
The best example of this is transcranial magnetic stimulation (TMS).
TMS is a method of non-invasive brain stimulation that can modulate neuronal activity. This technique was first used as an experimental research technique. More recently, the technique has provided effective therapy for a variety of disorders, including autism, depression, and schizophrenia.
What is TMS? 🧠
TMS is a ‘neuro-modulatory’. The technique can alter electrical activity in the brain via an electromagnetic pulse.
TMS produces a magnetic field around the skull. This field can manipulate electrical activity in the brain. The technique delivers an electrical current to a ‘coil.’ The coil is positioned beside the head and acts as a magnetic field generator. This magnetic field then generates an electric current within the brain via a pulse. In turn, this alters the activity of neuronal networks. These alterations can produce changes in behavior and sensory perception.
A wide variety of coils are available in different shapes and sizes. Scientists can target different brain regions by changing which coil they use. The most common part that TMS manipulates is a brain region known as the ‘cortex.’
The cortex enwraps the brain in thin, specialized layers of tissue. This thin cortical sheet gives our brains a distinctive wrinkly appearance. These wrinkles, known as ‘sulci’ and ‘gyri,’ are unique to humans. Cortical brain regions perform various executive functions such as attention and decision-making. These regions are also the primary regulators of social and emotional behavior.
The cortex is one of the critical regions of functional disruption in autism. The ability to alter and restore this balance within the cortex can improve symptoms.
Electrical activity and brain connectivity in autism 🧠
Brain imaging studies have shown abnormal patterns of activity in people with autism. Post-mortem studies have also revealed abnormalities in the local connections of cortical neurons. These findings suggest differences in brain connectivity at the micro and macro scale.
Researchers can measure patterns of electrical brain activity at the macro level. These patterns are known as ‘oscillations’ or brain rhythms. The synchronization of these brain rhythms allows harmonious communication between brain regions. Many studies have revealed differences in the brain rhythms of people with autism. Some have suggested that these alterations to brain waves are a biomarker for autism. Many scientists also believe these are the neural signatures that underlie autism symptoms.
Disruption to electrical activity within the brain looks to be a key feature of autism. Our ability to balance electrical activity may provide an effective treatment for autism.
How does TMS work as a therapy?
When first developed, the technique was used for experimental manipulations. This meant administering a single pulse via the coil to a specific region of the brain. Scientists could then assess behavior or sensory perception before and after the pulse. This revealed which brain regions were responsible for particular expressions and functions. This method is sometimes referred to as single-pulse TMS (spTMS).
In recent years, a technique known as repetitive TMS (rTMS) has become popular. rTMS uses the same technical principles as single-pulse TMS. But, as the name suggests, these pulses are applied several times in a row. The timing of these pulses changes depending on the desired effects. Different pulse timings will result in altered brain changes.
rTMS can be administered at both high and low-frequency levels. This level refers to the frequency band of the delivered pulses (e.g., high= 8Hz, low= 0.5Hz). Changes in frequency can alter which types of electrical brain activity are targeted. These changes can result in different effects.
rTMS is unique as the effects can lead to long last brain adaptations. In fact, in some cases, results can last for months. Interestingly, results can be seen as early as 1-2 weeks into the course.
Scientists still aren’t entirely sure how this works. However, they do have some speculations. Researchers think rTMS may cause these long-term brain changes by modulating processes of ‘brain plasticity.’ Plasticity can change how neuronal networks are connected. The therapy is also adaptable to the needs of the individual. For this reason, rTMS is the form of stimulation used in a clinical setting.
What happens during TMS therapy?
Before undertaking TMS therapy, all patients undergo a medical assessment. The patient’s doctor or psychiatrist will usually perform this. This is to ensure that the intervention is right for them. After this, clinicians will draw up a treatment plan based on evidence-based guidelines.
TMS therapy is usually an outpatient intervention. The intensity and length of the therapy will vary depending on the needs of the individual. Typically, sessions last for 30-40 minutes and take place five days per week, over 6 to 8 weeks.
Certified TMS technicians conduct the therapy sessions. These technicians will have received specialized theoretical and practical training. The TMS technicians will position the coil and apply the electromagnetic current. They can adapt to the timing and frequency of the pulse as needed. Technicians will also monitor progress and give regular check-ins with physical well-being.
TMS treatment schedules can be intensive. Due to this, technicians will try to make adjustments to the clinical environment. This helps to maximize patient comfort throughout the process. Comfort is important because patients must remain very still throughout the session. Excessive movement reduces the accurate targeting of specific brain regions.
How effective is TMS therapy for autism? 👨⚕️
Clinical use of TMS is becoming standard for the treatment of depression. This is where the technique has seen rapid advancement and successful outcomes. But there is growing evidence which suggests TMS may treat autism too.
Many studies have shown that low-frequency rTMS can improve some features of autism. In particular, this stimulation is helpful for repetitive behaviors. Research has shown that this may be due to a suppression of over-excitability in the cortex.
One clinical trial investigated low-frequency rTMS. The researcher applied this to the “prefrontal cortex”. The treatment took place over 12 sessions. The study found an improvement in the synchronization and power of brain rhythms. These rhythms, known as ‘gamma oscillations,’ have a critical role in cognition.
Gamma rhythms are a well-characterized biomarker for attention and executive function in humans. Hence, this study suggests rTMS may improve these cognitive capacities. The same study showed improvements in compulsive and repetitive behavior after rTMS treatment. Furthermore, some measurements of social behavior were also enhanced in these patients.
High-frequency rTMS has also been trialed in clinical populations. In one study, researchers gave high-frequency stimulation to ASD children with intellectual disabilities. Higher frequencies can increase cortical excitability.
Some scientists hypothesize that this may improve cognitive ability. The results were inconclusive regarding an improvement in cognitive and intellectual capacity. Despite this, researchers did find improved co-ordination.
A 2018 study found a ‘dose-dependent’ response between symptom severity and excitatory-inhibitory imbalance. Some studies have indicated that TMS interventions may address and improve this imbalance. As a result, some core features of autism may improve.
Research is evolving at a rapid pace. But, it’s vital to remember the need for large-scale and well-controlled studies. Unfortunately, these are still missing from the rTMS therapy for the autism research area. A recent review found many studies that had small sample sizes and poor controls. The authors of this study also noted a publication bias toward positive results. This is often prevalent in the scientific literature.
However, the same review identified many positive indications. They found many instances where rTMS can be useful for autism. They found the most robust results with functions such as attentional control. The study indicated that some features of autism did not change. This included slow reaction time and understanding the perspective of others.
rTMS may not be able to address all autism symptoms. But, it looks to have a positive effect on some core characteristics. The current consensus appears to be that rTMS can benefit patients with autism. Early indications suggest the therapy works for all age groups. The fact that the therapy is long-lasting and adaptable to the patient makes it appealing too.
How can I access TMS therapy? 👨⚕️
The clinical use of TMS is very safe, and adverse effects are rare. Rare side effects include fainting and seizures. People with epilepsy should discuss the suitability of this treatment with their doctor. Other rare side effects include mild discomfort and temporary hearing loss.
Patients who have implanted devices may experience the induction of these devices. Devices to be aware of include pacemakers and defibrillators. This is due to the electromagnetic field caused by the TMS coil. Doctors will consider these devices to make decisions on whether the therapy is appropriate.
Compared to other emerging therapies, TMS has lots of well-researched and evidence-based guidelines. These are available from the National Institute for Health and Care Excellence (NICE).
This allows interventions to incorporate a wealth of best practice protocols. Many of these guidelines relate to the treatment of conditions such as depression. But, research into the best practices for autism is evolving and improving.
Access to TMS therapies can vary across countries. In the UK, some NHS trusts do offer TMS for the treatment of some psychiatric conditions. The patient criteria for TMS therapy referral will vary a lot depending on the NHS region. However, there are increasing ways to access TMS therapy through private practice.
If you’re in the United States, the clinical TMS society has a variety of helpful resources. They can also help you find a licensed provider: https://www.clinicaltmssociety.org/.
No matter where you’re based if you’re looking to access TMS therapy, it’s important to research clinics. TMS technicians have professional training and certification. These technicians will usually have a background in medicine, psychology, or neuroscience.
They will have prior experience working with patients in a medical setting. People with autism often have complex needs. It may be worth look for technicians who have experience working with autism patients.
All patients should consult their doctor before starting TMS therapy.
The take-home message 📝
TMS has evolved from an experimental technique to a unique therapy. TMS appears to be able to provide positive benefits to many autism symptoms. However, larger-scale clinical trials and required to uncover what symptoms TMS can improve.
Autism is a lifelong disorder. Hence, it is vital to understand the long-term effects of TMS across all age-groups. At the moment, the intervention appears to be safe for children, adolescents, and adults. Future controlled clinical trials should confirm this.
TMS therapy looks like a positive intervention for autism. At present, scientists suggest TMS is useful add-on therapy for pre-existing treatment regimes. There are still some outstanding questions. Despite this, research is moving fast, and the future looks bright for TMS therapy.
Ashleigh Willis is a final year Ph.D. candidate in Neuroscience at the University of Glasgow. Her research investigates the genetic and environmental contributors to mental health and neurodevelopmental conditions. Ashleigh has built research collaborations with McGill University and received specialist training at the Centre for Neuroscience at Montreal General Hospital, McGill University Health Centre. She is also an active member of the Society for Neuroscience. Ashleigh holds an Honours in Psychology, an MRes in Neuroscience, and is fascinated by the neuronal circuits which make us who we are. Ashleigh is passionate about providing a deeper understanding of mental health conditions and sharing an accurate and de-stigmatizing message through talks for organizations such as TEDx, Pint of Science, and the Scottish Funding Council.
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