1. Developing Homogeneous Current Density Electrode Technology for Transcranial Direct Current Stimulation (tDCS)
AsMA May, 2015
R. Andy McKinley1
Mike Resor2
Haibo Dong2
Lindsey McIntire3
Justin Nelson3
Chuck Goodyear3
1Applied Neuroscience Branch
711th Human Performance Wing
Air Force Research Laboratory
2Wright State University
3Infoscitex, Inc

2. What is Non-Invasive Brain Stimulation?
Began as neurological therapeutic treatment
Two Primary Methods:
Transcranial Direct Current Stimulation
Transcranial Magnetic Stimulation
Healthy Controls – Improved Cognitive Performance
The primary technology we’ve been evaluating is non-invasive brain stimulation. Why non-invasive brain stimulation? Transcranial stimulation techniques originated in the clinical domain. Researchers have been investigating the utility of these stimulation techniques as a therapeutic treatment for a variety of neurological disorders such as Parkinson’s disease, major depressive disorder, stroke rehabilitation, chronic pain, etc. Several years ago, these investigators began to find cognitive improvements in their healthy control populations following some of their stimulation paradigms. As a result, we began investigation of these stimulation techniques as a way to bolster cognitive performance in Air Force specific domains.

3. Introduction Transcranial Direct Current Stimulation
So how does tDCS work exactly? Even though the exact mechanisms haven’t quite been uncovered, this is what is known currently:
Anodal stimulation up-modulates neural activity by decreasing the resting membrane potential making it easier for action potentials to occur. The result is an increase in spontaneous firing rate and an overall increase in regional cortical activity. Reversing the polarity (i.e. Cathodal stimulation) has the opposite effect.
When initially turned on, the stimulation creates some skin sensations such as itchiness, warming, or tingling. These sensations typically dissipate completely after a minute or two. Consequently, sham stimulation simply ramps the current up to the full level for 30 seconds and then turns off again. This provides the skin sensations similar to active stimulation without any significant cortical activation effects.

4. Has been shown to improve:
Speed of Response
Attention/Working Memory
Vigilance
Fregni, et al. 2005
Nelson, McKinley, et al. 2012
McKinley, et al. 2012
Language Learning
Declarative Memory
Spatial Tactile Acuity
Facts, General Knowledge
Events – e.g. daily activities
Sparing et al, 2008
Marshall et al, 2005
Ragert et al, 2008

5. High-Definition (HD) Electrodes
Current Technology
Saline soaked sponges
EEG-Based Electrodes
High-Definition (HD) Electrodes
Petree, et al. (2011)
REVS Neuroscience
Soterix Medical

6. Edge Currents Electricity follows the path of least resistance
High impedance of skin forces current to pool along outer edge of electrode
Krasteva ,V T and Papazov, S P, Estimation of Current Density Distribution Under Electrodes For External Defibrillation, BioMedical Engineering Online, 2002

7. Methodology Finite Element Modeling (FEM)
FEM model development & validation of skin-electrode interface
Krasteva ,V T and Papazov, S P, Estimation of Current Density Distribution Under Electrodes For External Defibrillation, BioMedical Engineering Online, 2002
50,000 mesh elements
Unstructured mesh
Our Model
100,000 mesh elements
Structured mesh
Validation

8. Five-Array EEG-based Electrodes
Max Delta Current Density A/m2

9. Design Ideas Square Spiral
Max Delta Current Density A/m2

10. Design Ideas Circular Spiral Electrode
Max Delta Current Density 1.27 A/m2

11. Design Ideas Flat Electrode
Max Delta Current Density A/m2

12. Design Ideas Concentric Electrode
Max Delta Current Density A/m2

13. Design Ideas Contoured Circular Array Electrode
Max Delta Current Density A/m2

14. Design Ideas “Star Fish” Array Electrode
Max Delta Current Density A/m2

15. Design Ideas Oval Contoured Array Electrode
Max Delta Current Density A/m2
- Cut the magnitude of the spike almost in half (0.352 A/m2 vs A/m2 )

16. Summary Max Delta Current Density 1.0 A/m2

17. Uniform Current Electrode

18. NIBS Team Justin Nelson, MS Andy McKinley, Ph.D. Lindsey McIntire, MS
Here’s the Non-invasive Brain Stimulation Team from WPAFB.
Will Tucker, MS
Kat Griffin, BS

19. Questions? R. Andy McKinley, Ph.D. Richard.McKinley.2@us.af.mil
I’d be happy to answer any questions you might have at this time. Thank you.