Gozde Unal, a PhD student in the lab of Dr. Marom Bikson will present her defense of her research proposal on Tuesday, May 11, 2021 at 9am. A copy of her abstract is below. If you would like to attend, please contact Gozde at gunal000@citymail.cuny.edu for the Zoom meeting ID.

ADAPTIVE CURRENT-FLOW MODELS OF ECT:

EXPLAINING INDIVIDUAL STATIC IMPEDANCE, DYNAMIC IMPEDANCE, AND BRAIN CURRENT DENSITY

Abstract

Improvements in electroconvulsive therapy (ECT) outcomes have followed refinement in device electrical output and electrode montage. The physical properties of the ECT stimulus, together with those of the patient’s head, determine the impedances measured by the device and govern current delivery to the brain and ECT outcomes. However, the precise relations among physical properties of the stimulus, patient head anatomy, and patient-specific impedance to the passage of current are long-standing questions in ECT research and practice.

We developed anatomical MRI-derived models of transcranial electrical stimulation (tES) that included changes in tissue conductivity due to local electrical current flow. These “adaptive” models simulate ECT both during therapeutic stimulation using high (~1 A) current and when dynamic impedance is measured, as well as prior to stimulation when low (~1 mA) current is used to measure static impedance. We modeled two scalp layers: a superficial scalp layer with adaptive conductivity that increases with electric field up to a subject specific maximum,

(σ_SS),

and a deep scalp layer with a subject-specific fixed conductivity,

(σ_DS).

We demonstrate that variation in these scalp parameters explain clinical data on subject-specific static impedance and dynamic impedance, their imperfect correlation across subjects, their relationships to seizure threshold, and the role of head anatomy. Adaptive tES models demonstrate that current flow changes local tissue conductivity which in turn shapes current delivery to the brain in a manner not accounted for in fixed tissue conductivity models.

Our predictions that variation in individual skin properties, rather than other aspects of anatomy, largely govern the relationship between static impedance, dynamic impedance, and current delivery to the brain, are themselves subject to assumptions about tissue properties. Broadly, our novel pipeline for tES models is important in ongoing efforts to optimize devices, personalize interventions, and explain clinical findings.

Zeinab Esmaeilpour, a PhD student in the lab of Dr. Marom Bikson will present her defense of her research proposal on Friday, April 2, 2021 at 3pm. A copy of her abstract is below. If you would like to attend, please contact Zeinab at zesmaei000@citymail.cuny.edu for the Zoom meeting ID.

Abstract

Understanding the cellular mechanism of direct current (DC) and kilohertz (kHz) electrical stimulation is of broad interest in neuromodulation in both invasive and noninvasive methods. More specifically there is large mismatch between enthusiasm to for clinical applications of the methods and understanding of DC and kHz mechanism of action. In the case of kilohertz stimulation, there is a well-established and validated low pass filtering characteristics of neuronal membrane. This feature attenuates sensitivity of nervous system to any waveforms with high frequency components. On the contrary, kilohertz stimulation has revolutionized spinal cord stimulation and even generated promising results in transcranial stimulation.

Effects DC stimulation have been studied in neuronal depolarization/hyperpolarization, synaptic plasticity and neuronal network modulation. Recent evidence suggests that DC stimulation can induce polarity dependent water exchange across blood brain barrier (BBB) in cell culture experiments through a mechanism called electroosmosis. Modulating water exchange rate across BBB is of broad interest in neurological disease such as dementia, Alzheimer’s, and stroke where brain clearance system is disrupted. Investigating effect of electrical stimulation on water exchange across BBB can potentially lead to therapeutic pathways.

This dissertation provides the first direct in vitro evidence on acute effects kilohertz electrical stimulation in central nervous system using both unmodulated and Amplitude-modulated waveforms. While supported by membrane characteristic of neurons, we uncovered that using low kilohertz stimulation diminishes the sensitivity of hippocampal neurons to electrical stimulation. Moreover, using Amplitude-Modulated waveform can generate a different pattern of modulation and even higher sensitivity to stimulation. However, required electric field in this case is significantly higher than low frequency stimulation methods such as tACS. We plan to study effect of direct current stimulation on water exchange rate across blood brain barrier (BBB) as new avenue of mechanism for electrical stimulation. We will investigate whether tDCS can increase water exchange rate and blood flow in healthy population using and advanced MR imaging technique.