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.

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. 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

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

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

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

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)

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

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

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. Under the brain, between the electrodes, under return but posterior of active

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

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

Future Work