1. 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 Laboratory
Department of Biomedical Engineering,
City College of the City University of New York, NY
*Research supported by The Wallace Coulter Foundation
Part II: [Many Applications need for more montages], Review tDCS (Mechanism, speak about directionality anodal/cathodal stim), historically montage design heuristic, but advances in modeling technique high resolution individualized models possible (videos of Obeses S1-3)… not always practical. Speak of constraints due to: high res MRI’s not always available, time (weeks of segmentation), computation resources (days to solve). Not always practical. Use high res models to create database of montages => this is part of that effort. (screenshot of Bonsai?) Compared to a purely heuristic approach: difference between stimulation “of” and “over”. => reference figures and explain.

2. 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.

3. Heuristic Montages
Traditionally montages have been created by “rule of thumb”
Active Pad over a target region.
tDCS has been around for years with roots in electrosleep
Many montages have been identified heuristically, they have been identified based on experience or common sense.
Examples of this include placing an “active” pads over a target region such as the Motorstrip, the Broca’s Area, or Wernicke's area. Typically the “return pad” is placed elsewhere.
But based on what we know about tDCS

4. Heuristic Montages
Traditionally montages have been created by “rule of thumb”
Active Pad over a target region.
tDCS has been around for years with roots in electrosleep
Many montages have been identified heuristically, they have been identified based on experience or common sense.
Examples of this include placing an “active” pads over a target region such as the Motorstrip, the Broca’s Area, or Wernicke's area. Typically the “return pad” is placed elsewhere.
But based on what we know about tDCS M1

5. Heuristic Montages
Traditionally montages have been created by “rule of thumb”
Active Pad over a target region.
tDCS has been around for years with roots in electrosleep
Many montages have been identified heuristically, they have been identified based on experience or common sense.
Examples of this include placing an “active” pads over a target region such as the Motorstrip, the Broca’s Area, or Wernicke's area. Typically the “return pad” is placed elsewhere.
But based on what we know about tDCS
Broca’s

6. Heuristic Montages
Traditionally montages have been created by “rule of thumb”
Active Pad over a target region.
tDCS has been around for years with roots in electrosleep
Many montages have been identified heuristically, they have been identified based on experience or common sense.
Examples of this include placing an “active” pads over a target region such as the Motorstrip, the Broca’s Area, or Wernicke's area. Typically the “return pad” is placed elsewhere.
But based on what we know about tDCS
Wernicke’s

7. Dorsal Lateral Prefronal Cortex
Heuristic Montages
Traditionally montages have been created by “rule of thumb”
Active Pad over a target region.
tDCS has been around for years with roots in electrosleep
Many montages have been identified heuristically, they have been identified based on experience or common sense.
Examples of this include placing an “active” pads over a target region such as the Motorstrip, the Broca’s Area, or Wernicke's area. Typically the “return pad” is placed elsewhere.
But based on what we know about tDCS
Dorsal Lateral Prefronal Cortex
(F8)

8. Heuristic Montages
Traditionally montages have been created by “rule of thumb”
Active Pad over a target region.
Return Pad is simply elsewhere.
tDCS has been around for years with roots in electrosleep
Many montages have been identified heuristically, they have been identified based on experience or common sense.
Examples of this include placing an “active” pads over a target region such as the Motorstrip, the Broca’s Area, or Wernicke's area. Typically the “return pad” is placed elsewhere.
But based on what we know about tDCS
F8 - SO

9. tDCS is Polarity Sensitive
Both the “Active” and “Return” stimulate (enhanced or suppressed excitability)
Polarity Dependent

10. An Alternative to Contralateral Supraorbital
Both the “Active” and “Return” stimulate (enhanced or suppressed excitability)
“2x1” Hybrid

11. The Finite Element Model
MRI Acquisition
Image Segmentation
Meshing
FEM Solution

12. Heuristic Design is Limited
The location of the return pad effects current distribution.
Under the brain, between the electrodes, under return but posterior of active

13. Stimulation “over” is not Stimulation “of”
Peak Electric field may or may not be on be directly under the active electrodes

14. Stimulation “over” is not Stimulation “of”
Peak Electric field may or may not be on be directly under the active electrodes

15. 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
Montages were modeled for our clinical colaborators

16. Future Work