Summary: Researchers reveal how targeting transcranial magnetic stimulation (TMS) could improve treatment of depression. The study identified an electrophysiological marker that could predict TMS effectiveness and guide personalized therapy. By optimizing the stimulation site and coil angle, treatment results can improve. These results give hope for better TMS therapies adapted to the future.
Highlights:
- Predictive biomarker: An electrophysiological marker could predict the success of TMS treatment.
- Personalized treatment: Optimizing the stimulation site and coil angle improves the effectiveness of TMS.
- Research potential: The results pave the way for more effective and individualized TMS therapies.
Source: University of Helsinki
Not all patients with depression respond to medications. Two recently published studies provide additional insight into how an alternative treatment, transcranial magnetic stimulation (TMS), could be further improved. TMS differs from electroconvulsive therapy (ECT), which is also used to treat depression.
Researchers from the University of Helsinki and Stanford University studied which TMS targeting factors influence the brain’s choices.
risky responses. They examined the behavior of a specific electrophysiological marker. This marker could potentially be used as a biomarker in the future to measure the effectiveness of TMS treatment and thus help target and tailor treatment.
“Magnetic stimulation is an effective treatment for patients whose depression is not relieved by medication. However, currently, about half of these patients do not receive significant help from TMS.
“The biomarker we studied could help predict who will benefit from the therapy. In the future, it may also be possible to adapt the treatment individually,” explains postdoctoral researcher Juha Gogulski from Stanford, the University of Helsinki and Aalto University.
Individual optimization is worth it
The first study focused on an electrophysiological marker describing cortical excitability and the sources of error affecting its measurement. Researchers studied healthy subjects to determine how magnetic stimulation targeted to the prefrontal cortex and the angle of the stimulation coil affected cortical excitability, that is, responses measured on an electroencephalogram (EEG) immediately after the stimulation pulse.
“The results showed that targeting the stimulation coil to different parts of the prefrontal cortex significantly affected the quality of electrical responses. Furthermore, we found indications that individual optimization of the stimulation site and coil angle could further improve the quality of this measurement,” says Gogulski.
The second study focused on the reliability of the same electrophysiological marker in the prefrontal cortex. The study found that the most important factor affecting reliability was the stimulation site.
“Before we can develop personalized TMS therapy, we need to ensure that the excitability of the prefrontal cortex can be measured as accurately as possible in each patient so that we can monitor how TMS treatment changes brain excitability. Determining reliability is also essential before this type of biomarker can be applied clinically,” says Gogulski.
Potential benefits are significant, more research needed
Magnetic stimulation already helps some people with depression, but Gogulski says the effectiveness of TMS therapy varies between individuals. More precisely tailored treatment could improve outcomes.
“There are many possible factors in TMS therapy that could be used for individual customization, such as stimulation site, number and frequency of pulses, stimulation intensity and number of treatment sessions. Side effects of TMS therapy are minimal, the most common being a temporary mild headache.
According to Gogulski, what makes these new studies significant is that this systematic and detailed mapping of the prefrontal cortex’s electrical responses and their reliability has never been done before.
Researchers hope that in the future, the effectiveness of TMS therapy can be monitored by measuring the brain’s electrical responses during treatment. Based on these measurements, it might be possible to fine-tune the stimulation if necessary, even during treatment.
“The results of both studies will be used in the future to design individual brain stimulation therapies based on electrical biomarkers. However, further research is needed before new treatment methods can be implemented,” says Gogulski.
About this research news on TMS and depression
Author: Aïno Pekkarinen
Source: University of Helsinki
Contact:Aino Pekkarinen – University of Helsinki
Picture: Image is credited to Neuroscience News
Original research: Free access.
“Mapping cortical excitability in the human dorsolateral prefrontal cortex” by Juha Gogulski et al. Clinical neurophysiology
Abstract
Mapping cortical excitability in the human dorsolateral prefrontal cortex
Background
Transcranial magnetic stimulation (TMS) of the dorsolateral prefrontal cortex (dlPFC) is an effective treatment for depression, but the neural effects after TMS remain unclear. TMS combined with electroencephalography (TMS-EEG) can causally probe these neuronal effects. Nevertheless, the variability of single-pulse TMS-evoked potentials (PET) in dlPFC subregions and potential artifacts induced by muscle activation require detailed mapping for precise treatment monitoring.
Objective
Characterize the first PETs anatomically and temporally (20 to 50 ms) close to the TMS pulse (EL-TEP), as well as associated muscle artifacts (<20 ms), across the dlPFC. We hypothesized that TMS location and angle influence EL-TEPs, and specifically that conditions with greater muscle artifact may have lower observed EL-TEPs due to excessive rejection. during pretreatment. Additionally, we sought to determine an optimal TMS target and angle at the group level, while investigating the potential benefits of a personalized approach.
Methods
In 16 healthy participants, we applied six-target single-pulse TMS in the dlPFC at two coil angles and measured EEG responses.
Results
Stimulation location significantly influenced the observed EL-TEPs, with posterior and medial targets producing larger EL-TEPs. Regions with high EL-TEP amplitude showed fewer muscle artifacts, and vice versa. The best group-level target gave 102% larger EL-TEP responses than other dlPFC targets. The optimal dlPFC target differed between subjects, suggesting that a personalized targeting approach could increase EL-TEP by an additional 36%.
Importance
EL-PETs can be probed without significant muscle-related confusion in the posteromedial regions of the dlPFC. The identification of an optimal target at the group level and the potential for further refinement through personalized targeting has significant implications for optimizing depression treatment protocols.