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

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.

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.

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

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

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

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

Five-Array EEG-based Electrodes Max Delta Current Density 0.665 A/m2

Design Ideas Square Spiral Max Delta Current Density 0.723 A/m2

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

Design Ideas Flat Electrode Max Delta Current Density 1.451 A/m2

Design Ideas Concentric Electrode Max Delta Current Density 1.409 A/m2

Design Ideas Contoured Circular Array Electrode Max Delta Current Density 0.477 A/m2

Design Ideas “Star Fish” Array Electrode Max Delta Current Density 0.3993 A/m2

Design Ideas Oval Contoured Array Electrode Max Delta Current Density 0.352 A/m2 - Cut the magnitude of the spike almost in half (0.352 A/m2 vs. 0.665 A/m2 )

Summary Max Delta Current Density 1.0 A/m2

Uniform Current Electrode

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

Questions? R. Andy McKinley, Ph.D. Richard.McKinley.2@us.af.mil 937-938-3598 I’d be happy to answer any questions you might have at this time. Thank you.