tDCS Electrode Placement Guidelines
For most clinical applications, place the anode over the target brain region to enhance excitability and the cathode on the contralateral supraorbital region, with the left dorsolateral prefrontal cortex (F3 position) being the most common target. 1
Fundamental Polarity Principles
The physiological effects of tDCS are polarity-dependent and determine electrode placement strategy:
- Anodal stimulation enhances cortical excitability of the underlying brain region through mechanisms similar to long-term potentiation 1, 2
- Cathodal stimulation reduces cortical excitability through long-term depression-like mechanisms 1, 2
- This polarity effect is mediated by NMDA receptor-dependent plasticity mechanisms 2
Standard Electrode Configurations by Target
Dorsolateral Prefrontal Cortex (Most Common Target)
Left DLPFC stimulation (used in 77 of 84 published studies):
- Anode placement: Left DLPFC at F3 position (10-20 EEG system) 1
- Cathode placement: Contralateral (right) supraorbital region 1
- This is the most frequently used configuration across clinical applications 1
Right DLPFC stimulation:
Motor Cortex (M1) Stimulation
For stroke rehabilitation and motor function enhancement:
- Anode placement: C3 (left hemisphere) or C4 (right hemisphere) position 1
- Cathode placement: Contralateral supraorbital region 1
- Stroke rehabilitation has Level B evidence supporting this configuration 3, 1
Important caveat for leg motor area: The conventional large-anode montage with contralateral supraorbital cathode produces non-specific effects affecting the contralateral hemisphere more strongly 4. For improved specificity when targeting leg motor cortex, use a smaller anode (3.5 cm × 1 cm at 0.2 mA) with cathode at T7 position 4.
Other Specific Targets
Inferior frontal gyrus:
Temporoparietal junction:
- Cathode placement: Over the target TPJ 1
- Anode placement: Occipital region 1
- Note this reverses the typical polarity when inhibition of TPJ is desired 1
Standard Technical Parameters
Electrode specifications:
- Standard electrode size: 5×7 cm (35 cm²) 1
- Current intensity: 2 mA 1
- Session duration: Up to 30 minutes 1, 2
- These parameters are considered safe based on extensive behavioral and neuroimaging studies 1, 2
Current density considerations:
- Smaller electrodes with equivalent current density at the surface produce similar excitability changes but improved spatial specificity 4
- Multiple electrodes of the same polarity can be arranged in a circle around the opposite polarity electrode to reduce current spatial variability 5
Critical Implementation Requirements
Complete documentation must include 1:
- Electrode material and contact medium
- Electrode size and geometry
- Precise placement relative to anatomical target
- Polarity assignment (anode vs cathode)
- Current density
- Rationale for chosen electrode locations
Common Pitfalls to Avoid
Contralateral effects: Large anodes with distant cathodes can produce stronger effects in the contralateral hemisphere than the targeted region, particularly for deep targets like leg motor cortex 4. Consider smaller electrodes with optimized cathode positioning for improved specificity.
Cathode location matters: While the anode position determines the primary target, cathode location significantly influences current flow patterns and can affect treatment outcomes 6, 4. The contralateral supraorbital position is standard, but alternative positions (e.g., T7 for leg motor cortex) may improve specificity 4.
Reproducibility challenges: Variability in electrode placement methods across studies contributes to inconsistent results 1. Use standardized positioning systems (10-20 or 10-10 EEG system) and document precisely 1.
Evidence Quality Considerations
The electrode placement recommendations are based on Level B evidence for motor rehabilitation applications 3, 1 and extensive consensus from international expert panels 3. The American Academy of Neurology supports these standardized protocols for therapeutic applications 1. However, methodological rigor and standardization remain critical barriers requiring improved reporting standards 3, 1.