What is Transcranial Magnetic Stimulation (TMS)?

Transcranial Magnetic Stimulation (TMS): Overview and Applications

Transcranial Magnetic Stimulation (TMS) is a non-invasive brain stimulation technique that uses brief focal electromagnetic pulses to penetrate the skull and stimulate targeted brain regions, inducing neuronal firing and modulating brain activity. 1

Basic Principles and Mechanism

TMS works based on the principle of electromagnetic induction:

• A copper coil positioned over the scalp generates a magnetic field that passes through the skull
• This magnetic field induces electrical currents in the underlying neural tissue
• The induced currents are strong enough to depolarize neurons and trigger action potentials 1
• TMS can modulate cortical excitability through mechanisms similar to long-term potentiation and depression, promoting brain plasticity 1

Types of TMS Protocols

TMS can be administered in several different formats:

• Single-pulse TMS (spTMS): Individual magnetic pulses used primarily for diagnostic purposes and measuring cortical excitability
• Paired-pulse TMS (PP-TMS): Two pulses delivered in sequence to assess inhibitory and excitatory circuits
• Repetitive TMS (rTMS): Trains of pulses delivered at specific frequencies
  • High-frequency rTMS (>5 Hz): Generally increases cortical excitability
  • Low-frequency rTMS (<1 Hz): Generally decreases cortical excitability 1
• Theta Burst Stimulation (TBS): Patterned rTMS with specific inter-train intervals
  • Intermittent TBS (iTBS): Typically increases cortical excitability
  • Continuous TBS (cTBS): Typically decreases cortical excitability 1, 2

Clinical Applications

TMS has been approved and used for various neuropsychiatric conditions:

• FDA-approved applications:

  • Major depressive disorder (strongest evidence base)
  • Obsessive-compulsive disorder
  • Smoking cessation 3

• Emerging applications with growing evidence:

  • Anxiety disorders (particularly with right DLPFC stimulation) 4
  • Post-stroke rehabilitation (motor recovery, aphasia) 1
  • Chronic pain conditions
  • Neurological disorders (migraine, dementia) 5

Treatment Parameters and Targeting

Critical parameters that affect TMS outcomes include:

• Stimulation target: Most commonly the dorsolateral prefrontal cortex (DLPFC)
• Stimulation frequency: High vs. low frequency depending on desired effect
• Stimulation intensity: Typically calibrated as a percentage of motor threshold
• Number of pulses: Total dose delivered per session
• Treatment duration: Number of sessions and schedule 1, 4

Advanced targeting methods include:

• Neuronavigation: Uses MRI-guided systems to precisely target specific brain regions 6
• Personalized targeting: Emerging approaches using individual neuroimaging data to optimize treatment 7

Safety and Side Effects

TMS is generally considered safe with minimal side effects:

• Most common side effects: Scalp discomfort, headache during or after treatment
• Rare but serious risk: Seizures (extremely uncommon with proper protocols)
• Contraindications: Metallic implants near the coil, history of epilepsy (relative), pregnancy (precautionary) 3

Future Directions

The field is advancing toward:

• More personalized TMS approaches based on individual neuroimaging and biomarkers 7
• Standardized protocols for specific conditions 1
• Combined approaches with other treatments (medication, psychotherapy)
• Improved understanding of neurobiological mechanisms 2

TMS represents a significant advancement in non-invasive neuromodulation with growing applications across psychiatry and neurology, offering an alternative treatment option for patients who don't respond to conventional therapies.