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Seminar
Memory of Time and Functional Restoration of Visual Circuits
Speaker Prof Jiayi Zhang
Institute of Brain Science, Fudan University, China
Date 17 January 2017 (Tuesday)
Time 15:00 – 16:00
Venue Room 5506 (Lifts 25-26), HKUST
Abstract
I will briefly cover two (maybe three) interesting stories: (1) Learning to recognize temporal patterns is a fundamental feature for sensory perception and cognition. Representation of timing in multi-second range has been thought to involve prefrontal and posterior parietal cortices. Much more work is needed for a deeper understanding of whether timing information is retained in primary sensory cortex. We recorded both local field potentials (LFP) and spiking activities in primary visual cortex (V1) after periodic visual stimulation in the order of seconds in lightly anaesthetized and awake mice. The post-stimulation LFP events in V1 showed a regular interval and phase that closely matched the stimulus. Inter-spike intervals had a similar entrainment to the stimulus interval. The emergence of these temporally entrained events required at least 10 periodic stimulations and persistent but not transient firing responses to light. Periodic optogenetic stimulations on ChR2-expressing CaMKII$\alpha$ in V1 induced similar entrainment. Rewardconditioned responses, visuomotor behavior and simultaneous electrophysiological recording showed post-stimulation entrainment to stimulus timing in awake-behaving mice. In vivo patch recording further revealed that the synaptic connections are stronger during entrainment. These experiments demonstrate that spontaneous activities in V1 can retain the timing information of visual stimulus, and serve as a mechanism for short-term response to rhythmic sensory experience. (2) The restoration of light response with complex spatiotemporal features in retinal degenerative diseases towards retinal prosthesis has proven to be a considerable challenge over the past decades. The state-ofart retinal prosthesis utilizes photodiode arrays fabricated on solid substrates, which cannot be easily adapted to the curvature of the eyeball and cover the entire visual field. Polymer based optoelectronic interface to retinal tissue, despite being compatible with flexible substrates, has limited spatial resolution for vision. Herein, inspired by the structure and function of photoreceptors in retinas, we developed bioinspired artificial photoreceptors, i.e. gold nanoparticle-decorated titania (Au-TiO2) nanowire arrays, for restoration of multi-color visual responses in the retina of blind mice with degenerated photoreceptors. When Au-TiO2 nanowire arrays were in direct contact with blind mice retina, single-cell intracellular measurements by patch-clamps in the retinal ganglion cells (RGCs) revealed that green, blue and UV light responses were restored with a spatial resolution approaching or exceeding 100 µm. Light responses in RGCs exhibited diverse patterns including ON and OFF, indicating that nanowire array-interfaced retinas were capable of processing visual information through innate retinal circuits. Moreover, functional calcium imaging demonstrated cellular-level population responses in the Au-TiO2 nanowire array-interfaced blind retinas. This study is among the first to show bio-inspired artificial photoreceptors and will shed light on the development of a new generation of optoelectronic toolkits for photo-coded subretinal implants and prosthetic devices.
DEPARTMENT OF PHYSICS