High-Density Fiberless Optoelectrodes with Integrated Waveguides and LEDs

The study of a localcuit inside the brain requires a tool to precisely modulate a few selected neurons and simultaneously monitor the neuronal responses. Optogenetics provides the capability to excite or inhibit activities of specific neurons in intact animals with millisecond precision. This light-induced stimulation technique can be combined with electrophysiology to enable simultaneous control of target neurons and recording of the associated neuronal activities in the brain. In this chapter, we introduce the state-of-the-art optoelectrodes that enable precise optical stimulation and electrical recording in behaving animals. For experiments with behaving animals, it is important that the light sources are integrated within the headstage so that light can be delivered to multiple stimulation sites without causing a tethering problem. Two fiberless implementation approaches that promote easier scaling are discussed in detail: the integration of optical waveguides on the probe shank for light delivery to a distal end located near the recording electrodes and the direct integration of neuron-sized (similar to 10 mu m) microLEDs in the vicinity of the recording electrodes. The design principles and the fabrication processes, as well as the advantages and the limitations of each approach, will be presented along with the results of in vivo validation experiments.