טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentYona Guy
SubjectNovel Tools for Probing the Motor Control System in Behaving
Animals
DepartmentDepartment of Autonomous Systems and Robotics
Supervisors Professor Itamar Kahn
Professor Shy Shoham


Abstract

A thorough systems-based dissection of the neural circuits involved in motor behavior, and particularly locomotion, poses major challenges. These underlying difficulties include a strong coupling with sensory and internal motivational systems, precluding a clearly defined input, the extensive involvement of deep brain structures, and the unavoidable motion of the animal under investigation. In this work, three novel tools for control and observation in behaving animals are introduced, promoting the decoupling of the sensory input from the motor system and facilitating the study of individual system components.

Optogenetics, the ability to control cell type-specific activity with light, has in recent years become a central tool in neuroscience research. Estimating the transmission of visible light through brain tissue is of crucial importance for controlling the activation levels of neurons in different depths, and designing the optical systems. Analytical models and Monte-Carlo simulations previously used to model light propagation through rodents' brain tissue suffer from fundamental shortcomings. Here, a new analytical approach is introduced for modeling the distributions of light emanating from a multimode fiber and scattering through tissue. A good agreement of the new methods' predictions both with recently published data, and with new measurements in mouse brain cortical slices is introduced. The described results yield a new cortical scattering length estimate significantly shorter than ordinarily assumed in optogenetic applications.

To allow optogenetic control across extensive regions, a solution is presented that is based on the development of a holographic optogenetics pattern stimulation system for spatiotemporally controlling large-scale cortical populations. The system transmits optical patterns created by computer-generated holography through a custom optical fiber bundle onto a chronic implant in the mouse cortex. The design of this in vivo system required addressing the strong scattering of visible light in the brain, which was overcome by using an array of optical needle-shaped wave-guides protruding the cortex, and delivering light into deeper layers. The described solution also overcomes optical coupling and manufacturability issues associated with designing a chronically implanted, detachable connector, using miniature 3D printed parts and micro-manufactured glass components. To measure whole-brain activity during self-motivated locomotion, a 3D-printed MRI cradle for mice that incorporates a rotating treadmill was developed. The animal is head-fixed to a bridge on top of the apparatus, and can run freely on the treadmill belt whose position is continuously logged and filtered during a functional MRI scan.

We describe extensive experimental validations of the new systems, demonstrating how whole-brain imaging of the locomotion network can provide insights on the organization of this system. Specifically, separate motivational systems that drive distinct behavioral groups, and the location and extent of the mesencephalic locomotor region are presented. This work enables the investigation of the basic locomotion circuit, observed in its entirety for the first time in behaving animals. Using animal disease models, this approach will facilitate the investigation of motor system pathologies, such as Parkinson's disease, and their influence on functional organization and activity in related brain networks, potentially leading to new interventional targets for ablation or control with deep brain stimulation.