Mechanisms of transcranial alternating current stimulation (TACS) in awake non-human primates
(A) TACS set-up with single-neuron recordings. (B) Three TACS intensities. (C) Example of a single channel data and spike extraction. (D) Butterfly plot of spike waveforms before and during stimulation. (E) The raster plots of the spiking before and after stimulation (in black) and during stimulation (in orange) in one exemplary neuron.
Intensities of tACS affect change spike timings and create neural entrainment in single cells. PLV values during stimulation are enhanced during all intensities and increasingly so for higher intensities for responsive neurons while the spiking rate during tACS for all neurons and responsive neurons is quite similar regardless of the tACS intensity.
Investigating TMS neural responses in non-human primates
The neural mechanisms of TMS are still not fully understood. We study the effects of TMS in a non-human primate model with electrophysiological recordings. Analysis of this electrophysiological data shows an early TMS-evoked potential component (N50) that is dose and stimulation location dependent. Electric field modeling can further explain these differential effects.
Cross-Species Modeling for Translational Research
Closed-Loop Real-Time TMS-EEG in Humans
TMS enables non-invasive perturbation of brain activity in humans. Its repeated application over the left prefrontal cortex is effective for the treatment of depression. However, there is significant variability in treatment outcomes across patients. We hypothesize that aligning TMS pulses to the "context" of the ongoing brain activity (EEG) using a closed-loop real-time approach will improve the effectiveness of the stimulation.
(Left.) Real-time closed-loop phase detection. EEG is recorded and streamed to the computer. The alpha band from the region of interest is extracted by bandpass filtering. The signal is forward predicted. TMS is delivered at the upcoming peak (excitable brain state). (Right.) Experimental setup for real-time closed-loop TMS-EEG.
Multi-Scale Modeling from Whole Brain to Single Neuron Level
Multi-scale modeling can complement experimental research by providing a framework between the physical input parameters of TMS and the cellular and subcellular neural effects of TMS. We developed a multi-scale Neuron Modeling for TMS toolbox (NeMo-TMS) that enables researchers to easily generate accurate neuron models from morphological reconstructions, couple them to the external electric fields induced by TMS, and to simulate the cellular and subcellular responses of the neurons.
Brain Stimulation for Stroke Recovery in Children
Ischemic perinatal stroke affects as many as 1 in 2,300 live births. Transcranial magnetic stimulation (TMS) and transcranial electric stimulation (TES) have shown promise as noninvasive cortical assessment and neuromodulation techniques for stroke rehabilitation. We are integrating individual realistic head models into the therapy to optimize neuromodulation targets for rehabilitation in perinatal stroke. Using our novel computational method, we are able to develop more precise and effective personalized treatments for stroke rehabilitation.
(Left) Individual head models from patients' MRI are made using the finite element method (FEM). Anatomically accurate representation of a lesion is a crucial step for patient-specific modeling. (Right) Simulation of the electric field during TMS over the lesioned (left) and non-lesioned (right) hemispheres. A) TMS coil over the motor cortex. B) TMS coil over the temporal lobe. We conduct FEM simulations to understand how electric fields change for different brain anatomy and in the presence of a lesion.
Novel Dynamic Methods of TACS
Transcranial alternating current stimulation (TACS) is an emergent method of non-invasive neuromodulation that can engage frequency-specific brain oscillations. We propose a new application of multi-channel TACS to hyper- or de-synchronize distant brain regions by driving them with the same frequency but at different phases.