Prefrontal Cortex transcranial Direct Current Stimulation via a Combined High

Definition and Conventional Electrode Montage: A FEM modeling study

Dennis Q. Truong, Abhishek Datta, Jiansong Xu, Felipe Fregni, and Marom Bikson

Neural Engineering LaboratoryDepartment of Biomedical Engineering,

City College of the City University of New York, NY

*Research supported by The Wallace Coulter Foundation

tDCS Basics

• Typically subthreshold brain stimulation – Action potentials are not

directly caused, rather excitability is enhanced or suppressed

• Enhanced or Suppressed cortical excitability is due to polarity.

Heuristic Montages

• Traditionally montages have been created by “rule of thumb”– Active Pad over a target region.

Heuristic Montages

• Traditionally montages have been created by “rule of thumb”– Active Pad over a target region.

M1

Heuristic Montages

• Traditionally montages have been created by “rule of thumb”– Active Pad over a target region.

Broca’s

Heuristic Montages

• Traditionally montages have been created by “rule of thumb”– Active Pad over a target region.

Wernicke’s

Heuristic Montages

• Traditionally montages have been created by “rule of thumb”– Active Pad over a target region.

Dorsal Lateral Prefronal Cortex

(F8)

Heuristic Montages

• Traditionally montages have been created by “rule of thumb”– Active Pad over a target region.– Return Pad is simply elsewhere.

F8 - SO

tDCS is Polarity Sensitive

• Both the “Active” and “Return” stimulate (enhanced or suppressed excitability)

An Alternative to Contralateral Supraorbital

• Both the “Active” and “Return” stimulate (enhanced or suppressed excitability)

“2x1” Hybrid

The Finite Element Model

MRI Acquisition

Image Segmentation Meshing FEM Solution

Heuristic Design is Limited

• The location of the return pad effects current distribution.

• Peak Electric field may or may not be on be directly under the active electrodes

Stimulation “over” is not Stimulation “of”

• Peak Electric field may or may not be on be directly under the active electrodes

Stimulation “over” is not Stimulation “of”

Summary• Montage design does not obey a

simple rule of thumb.– Active Electrodes do not necessarily

cause peak field at the target.– Return Electrodes need to be carefully

considered.

• Big Picture: Clinicians could use better guidelines for montage designs. i.e. – database of montage models

Future Work