A New Angle on Transcranial Magnetic Stimulation Coil Orientation: A Targeted Narrative Review.

Area of Science:

• Neuroscience
• Neurology
• Biomedical Engineering

Background:

• Transcranial magnetic stimulation (TMS) treats neuropsychiatric disorders like depression, but efficacy varies.
• Treatment outcomes depend on stimulation parameters, with coil orientation being underexplored.
• Current coil orientation practices are based on motor cortex anatomy, potentially suboptimal for other brain regions like the dorsolateral prefrontal cortex.

Purpose of the Study:

• To review evidence on the impact of TMS coil orientation on neuronal response and clinical outcomes.
• To evaluate how coil orientation interacts with TMS electric fields, head tissue conductivity, and cortical anatomy.
• To propose optimizing coil orientation as a critical parameter for therapeutic TMS.

Main Methods:

• Targeted narrative review of experimental, clinical, and computational studies.
• Analysis of electric field properties induced by TMS.
• Examination of how coil orientation affects cortical activation magnitude and location.

Main Results:

• Coil orientation significantly influences the electric field distribution and subsequent neuronal activation.
• Evidence suggests that current coil positioning may not be optimal for targeting specific brain networks in conditions like depression.
• Optimizing coil orientation can impact TMS dosing and brain network engagement, key factors for clinical response.

Conclusions:

• Coil orientation is a critical, yet often overlooked, parameter in therapeutic TMS.
• Revising coil orientation strategies, potentially away from motor cortex-based methods, could enhance TMS efficacy.
• Further research and clinical application should consider optimizing coil orientation for improved treatment outcomes in neuropsychiatric disorders.