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Optics and Electronics Seminar
Apr 24, 2017
4:15 PM, Spilker 232
http://campus-map.stanford.edu/index.cfm?ID=04-040 - Map
ULTRASONIC NEUROSTIMULATION IN THE RETINA
Stephen A. Baccus
Dept. of Neurobiology
Noninvasive neurostimulation with near-cellular spatial resolution has applications
both in the clinic for diagnosis or therapy of disease, and for basic understanding
of neural circuits. Ultrasound is best known for imaging biological tissue, but it
has recently been shown that ultrasound can stimulate and modulate neural activity.
Although this approach has the potential to reach anywhere in the brain noninvasively,
the capabilities of ultrasound have not been fully realized, in part because its mechanisms
of action in the nervous system are not well understood.
The retina is a thin sheet of neural tissue with an intricate network of cells that heavily processes visual images before transmission through the optic nerve. We have used the in vitro retina as a test bed to characterize the capabilities of ultrasonic neurostimulation and to understand its mechanisms and effects on neural circuits. I will discuss our studies showing that ultrasound can stimulate retinal neurons with high spatial and temporal precision approaching that achievable with visual stimuli. We have further combined ultrasonic stimulation with optical imaging to observe microscopic mechanical displacements that indicate that radiation pressure is the likely physical mechanism through which ultrasound activates the retina. I will further discuss the prospects for ultrasonic neurostimulation elsewhere in the brain and its potential use as a neural prosthesis.
We study how the circuitry of the retina translates the visual scene into electrical
impulses in the optic nerve. Visual perception is initiated by the molecules, cells
and synapses of the retina, acting together to process and compress visual information
into a sequence of spikes in a population of nerve fibers. One of the largest gaps
in neuroscience lies in the explaining of systems-level processes like visual processing
in terms of cellular-level mechanisms. This problem is tractable in the retina because
of its experimental accessibility, and the substantial amount already known about
basic retinal cell types and functions.
Our goal is to extract general principles of computation in neural circuits, and to explain specific retinal visual processes such as adaptation to contrast and image statistics, and the detection of moving objects. To do this, we use a versatile set of experimental and theoretical techniques. While projecting visual scenes from a video monitor onto the isolated retina, an extracellular multielectrode array is used to record a substantial fraction of the output of a small patch of retina. Simultaneously, we record intracellularly from retinal interneurons in order to monitor and perturb single cells as the circuit operates. To measure the activity of both populations of interneurons and output neurons, we record visual responses optically using two-photon imaging while simultaneously recording with a multielectrode array. Finally, all of this data is assembled and interpreted in the context of mathematical models to predict and explain the output of the retinal
An additional focus of the lab is to develop approaches to stimulate the nervous system using focused ultrasound. Recent studies have shown that ultrasound can activate the retina with high spatial and temporal precision. This technology holds promise as a noninvasive tool to study the brain and treat diseases of the nervous system both in the retina and elsewhere in the brain.