Nir Grossman received a BSc in Physics from the Israeli Institute of Technology (Technion) and a MSc in Electromagnetic Engineering from the Technical University of Hamburg-Harburg (TUHH), Germany. He then moved to the Department of Medicine at Imperial College London to conduct PhD training under the supervision of Patrick Degenaar and Christopher Kennard. His PhD thesis investigated a new type of retinal prosthesis that uses genetic expression of microbial light sensitive ion channel, Chanelrhodopsin-2 (ChR2) and remote light stimulations. Nir is currently a BBSRC (Biotechnology and Biological Sciences Research Council) Enterprise Fellow in the laboratory of Christofer Toumazou at the Institute of Biomedical Engineering at Imperial College.
Studying neuronal processes such as synaptic summation, dendritic physiology and neural network dynamics requires complex spatiotemporal control over neuronal activities. The recent development of neural photosensitization tools, such as channelrhodopsin-2 (ChR2), offers new opportunities for non-invasive, flexible and cell-specific neuronal stimulation. Previously, complex spatiotemporal control of photosensitized neurons has been limited by the lack of appropriate optical devices which can provide 2D stimulation with sufficient irradiance. We developed a solution that is based on an array of high-power micro light-emitting diodes (micro-LEDs) that can generate arbitrary optical excitation patterns on a neuronal sample with micrometre and millisecond resolution.
Modeling Study of the Light Stimulation of a Neuron Cell with Channelrhodopsin-2 Mutants
Channelrhodopsin-2 (ChR2) has become a widely used tool for stimulating neurons with light. Nevertheless the underlying dynamics of the ChR2-evoked spikes are still not yet fully understood. Here we develop a model that describes the response of ChR2-expressing neurons to light stimuli and use the model to explore the light-to-spike process. We show that an optimal stimulation yield is achieved when the optical energies are delivered in short pulses. The model allows us to theoretically examine the effects of using various types of ChR2 mutants. We show that while increasing the lifetime and shuttering speed of ChR2 have limited effect, reducing the threshold irradiance by increased conductance will eliminate adaptation and allow constant dynamic range. The model and the conclusions presented in this study can help to interpret experimental results, design illumination protocols and seek improvement strategies in the nascent optogenetic field.
Investigation of the activation mechanisms of transcranial magnetic stimulation (TMS)
External electromagnetic (EM) stimulation tools such as transcranial magnetic stimulation (TMS) are rapidly developing non-invasive tools for studying human brain function and for therapeutic applications nevertheless, the precise mechanism of its activation is mostly unknown. Improving our understanding of the fundamental principles of this technique is key for overcoming its limitations such as poor efficiency and lack of cell specificity and will improve its overall therapeutic acceptance. This project explores the underlying mechanisms of electromagnetic stimulation.