M.Sc Thesis

M.Sc StudentGolan Lior
SubjectA Holographic Method for Neuronal Dynamic Patterned
DepartmentDepartment of Biomedical Engineering
Supervisor PROF. Shy Shoham
Full Thesis textFull thesis text - English Version


Degenerative diseases of the outer retina lead to photoreceptor dystrophy and eventually to blindness. Retinal prostheses based on neuronal stimulation with micro-electrodes are being employed to restore visual input.  Optical photo-stimulation has been suggested as a minimally-intrusive and precise alternative for electrical stimulation. Recently-proposed photo-stimulation techniques such as optogenetics and photo-thermal stimulation hold promise for constructing a stable neural interface, but require intense, high-resolution light patterns to control large neuronal populations, potentially with a single-cell resolution.

In this study, we explore the projection of photo-stimulation patterns using phase-only holography. We present a computer-generated holography system, based on a liquid-crystal Spatial Light Modulator (SLM), for creating precise, rapidly-changing light patterns for photo-stimulation. Holographic projection offers parallel stimulation in two or three dimensions with high intensity and a millisecond time-scale. Our optical system is integrated with a commercial microscope, enabling simultaneous imaging and stimulation of neural tissue samples. The system is also integrated with single- and multi-unit electrophysiology systems so recording is also enabled.

In holographic systems, every projected pattern requires the design of a unique hologram. We study the hologram design problem, keeping in mind that computational complexity is critical for implementation in a real-time system. However, typical properties of photo-stimulation patterns can be exploited to achieve simpler algorithms. Special attention is given to the limitations imposed by the SLM when generating two- and three-dimensional patterns.

We demonstrate how rapid projection of hologram sequences can be used to enhance system performance. In particular, the speckle problem encountered in holographic projection is discussed, and a simple sequence 'shift-averaging' solution is proposed and analyzed.

Finally, we validate the functionality of the system by in-vitro experiments in live retinas. In addition, we perform temperature measurements to characterize the thermal transients created by the system during photo-thermal stimulation. We conclude by discussing the advantages, challenges and future directions for the holographic photo-stimulation technology