|M.Sc Student||Matar Suhail|
|Subject||Diffractive Multiphoton Neural Interface|
|Department||Department of Biomedical Engineering||Supervisor||PROF. Shy Shoham|
|Full Thesis text|
Over the past few years, optical technologies for the stimulation and imaging of neural populations have been generating much enthusiasm in the field of neural research. Here we show the application of two new neural interfaces - one for stimulation and another for imaging - that are based on diffractive optics.
The first interface incorporates a phase-only Spatial Light Modulator, used to display Computer Generated Holograms. The system can create user-defined dynamic, three-dimensional light patterns from an ultrafast laser beam, enabling multi-target, two-photon optical neural stimulation. We demonstrate the system’s capabilities by using a novel, thermal-based neural photostimulation method. The method relies on heating micron-sized absorbing particles using short laser pulses. This induces thermal transients in the vicinity of the particles, activating neurons. We show results from physiological experiments in which neurons were stimulated using this method, with laser pulses only a few tens of microseconds long and pulse energies of only a few tens of nano-Joules. We also investigate and assess the temperature rise caused by the particles’ heating using Fluorescent Microthermal Imaging. Such a diffractive interface, coupled with the new photostimulation method, could prove to be a promising basis for cortical neuroprostheses.
The second, imaging interface uses a Resonant Grating Waveguide Structure - a specially designed glass slab - as a platform on which neural cultures are grown for optical recording. When a laser beam is coupled into such a structure, it is diffracted by dint of an embedded grating structure. At a suitable angle of incidence, the first diffraction order is coupled into the slab and is guided along, producing an evanescent wave phenomenon on the slab’s surface. This wave is used here to image the parts of cells closest to the surface with potentially reduced photobleaching and photodamage. This interface could also serve as a tool for investigating membrane-related phenomena.