טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentLior Golan
SubjectA Holographic Method for Neuronal Dynamic Patterned
Photostimulation
DepartmentDepartment of Biomedical Engineering
Supervisor Full Professor Shoham Shy
Full Thesis textFull thesis text - English Version


Abstract

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