Transcranial Magnetic Stimulation: Stroke Risk And Real Dangers?

Transcranial magnetic stimulation (TMS) is a non-invasive tool that has been used to investigate the brain plasticity changes resulting from stroke and as a therapeutic modality to safely improve motor function. TMS can be used to stimulate the primary motor cortex (M1) to activate corticospinal neurons transsynaptically, eliciting volleys of neuronal output in the form of motor evoked potentials (MEP).

TMS has been shown to improve upper limb recovery in stroke patients. It has also been used to treat dysphagia, speech impairments, central post-stroke pain, depression, and cognitive dysfunction.

TMS is believed to rely on principles of long-term potentiation/depression (LTP/LTD)- synaptic plasticity that has been extensively studied at the cellular level.

Motor rehabilitation

RTMS can be used to stimulate the affected hemisphere, or the unaffected hemisphere, with the aim of restoring balance between the two. The former is achieved by applying high-frequency rTMS, which increases cortical excitability, while the latter is achieved by applying low-frequency rTMS, which decreases cortical excitability.

RTMS can be combined with other rehabilitation techniques, such as physical therapy, to improve motor function.

RTMS has been shown to improve upper limb function, lower limb function, and balance function. It can also be used to treat dysphagia, depression, and cognitive impairment.

The molecular and cellular mechanisms underlying rTMS-mediated stroke rehabilitation include the regulation of neurotransmitters, immune cells, and inflammatory cytokines.

RTMS can be used to modulate the activity of astrocytes and microglia, which are important in the maintenance of the blood-brain barrier and CNS homeostasis.

RTMS has been shown to be safe, with only minor side effects such as tingling sensations and headaches. However, there is a risk of epileptic seizures if safety guidelines are not followed.

Speech rehabilitation

Improving Language and Speech Functions

RTMS can target specific brain regions to enhance language and speech functions. It has been found to improve naming abilities, propositional speech, and overall language performance in stroke patients with aphasia. This includes improvements in fluency, phrase length, and the ability to express thoughts and ideas.

Enhancing Brain Plasticity

RTMS can also promote brain plasticity changes, which are essential for recovery. By inhibiting over-activation in the right hemisphere and modulating activity in the left hemisphere, rTMS helps restore balance and facilitate reorganization. This can lead to improved language and speech functions.

Increasing Neurotransmitter Release

RTMS can modulate the release of neurotransmitters, such as glutamate and GABA, which play a crucial role in synaptic function and neural communication. By regulating these neurotransmitters, rTMS can influence excitatory and inhibitory processes in the brain, promoting recovery.

Reducing Neuroinflammation

Neuroinflammation is a key factor in stroke and its aftermath. rTMS has been shown to reduce neuroinflammation by regulating immune cells, such as microglia and astrocytes, and inflammatory cytokines. This anti-inflammatory effect contributes to neuroprotection and recovery.

Combining rTMS with Traditional Rehabilitation

RTMS is often combined with traditional speech and language therapy to enhance its effectiveness. This combination therapy has shown promising results in improving language and speech functions, especially when started early after a stroke.

Imaging Techniques for Evaluation and Optimization

Imaging techniques, such as fMRI and DTI, play a vital role in understanding the mechanisms of rTMS and optimizing its application. They can help identify target brain regions, assess treatment effects, and guide the development of personalized rTMS protocols for individual patients.

Central post-stroke pain

CPSP is caused by damage that disturbs signals along the pain-transmission pathway, from the sensory cortex to the thalamus. The condition is rare, occurring in an estimated 2% to 5% of all stroke cases. Antidepressants, including tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors, and selective serotonin reuptake inhibitors, are used most frequently for the treatment of neuropathic pain, although there is little published evidence of their effectiveness in CPSP. Treatment for patients resistant to first- and second-line treatment can include opioids or tramadol. Caution is advised for the use of opioids as there is a significant risk of physical dependency.

An important component of CPSP treatment is the involvement of an interdisciplinary team that includes healthcare professionals with expertise in mental health and central pain management.

Cognitive impairment

Transcranial magnetic stimulation (TMS) is a non-invasive technique that can be used to improve motor function in stroke patients. It can also be used to treat cognitive impairment, which is a common complication of stroke.

TMS has been shown to improve cognitive function in patients with mild cognitive impairment and Alzheimer's disease. The technique can be used to stimulate the dorsolateral prefrontal cortex and the cerebellum, and it has been found to be most effective when applied at moderate frequencies (5Hz and 10Hz).

The exact mechanisms by which TMS improves cognitive function are not yet fully understood, but it is thought to involve the regulation of neurotransmitters, immune cells, and inflammatory cytokines. TMS has been shown to modulate the release and expression of neurotransmitters such as glutamate, GABA, glycine, and acetylcholine. It also regulates the activation and polarization of astrocytes and microglia, which are types of glial cells that play important roles in the brain's immune response and maintenance of homeostasis. Additionally, TMS has been found to alter the expression of inflammatory cytokines, which are proteins that mediate immune and inflammatory responses.

Overall, TMS is a promising technique for improving cognitive function in patients with stroke-related cognitive impairment, but further research is needed to fully understand its mechanisms of action and optimize its therapeutic potential.

Depression

Transcranial Magnetic Stimulation (TMS) is a non-invasive form of brain stimulation that has been used to treat depression. It operates completely outside of the body, affecting the central nervous system by applying powerful magnetic fields to specific areas of the brain involved in depression. TMS does not require anaesthesia and is generally well-tolerated, with the most common side effect being headaches during or after treatment.

First-line treatments for depression include antidepressants and psychotherapy, but these do not work for everyone. Electroconvulsive therapy (ECT) has long been considered the gold standard for treatment-resistant depression, but its side effects on memory and cognition can be difficult for some people to tolerate. For these individuals, TMS has emerged as a newer treatment option.

TMS therapy is an intensive treatment, requiring sessions five days a week for several weeks. Each session may last anywhere from 20 to 50 minutes. During treatment, an electromagnetic coil is placed on the scalp, generating a pulsatile magnetic field that depolarises cortical neurons. The levels of neuronal stimulation can be regulated, with high-frequency stimulation of the left dorsolateral prefrontal cortex (DLPFC) alleviating depressive symptoms, and low-frequency cortical stimulation of the right DLPFC helping to relieve symptoms of both depression and anxiety.

Several studies have demonstrated the effectiveness of TMS in treating depression. A literature review reported that response rates to TMS range between 50% and 60%, with about one-third of individuals experiencing a full remission of symptoms. Another randomised multicenter trial showed that TMS had significant antidepressant effects, with remission rates four times higher than placebo. TMS was also found to improve all symptoms of depression on the Hamilton depression rating scale.

While the neurobiological phenomena underlying the effectiveness of TMS as an antidepressant are not yet fully understood, studies have suggested a correlation between cerebral metabolic activity and TMS effectiveness. Neuronal physiology that responds to TMS is also important, as repetitive stimulations increase synaptic plasticity, causing it to last longer even after stimulation ceases.

Frequently asked questions