ABSTRACT
This chapter aims to describe approaches for optical stimulation of neural circuits in freely behaving animals. Merely observing which aspects of neural activity are correlated with a given behavior may provide invaluable information about the system, but to causally define it, the underlying circuit dynamics must be manipulated. To better confine the distribution of exiting light and alleviate some of the pressure on neural tissue, waveguide dimensions can be greatly reduced by de novo fabrication, chemical etching in acidic solution, machining, or heating and pulling. Electrical recordings enjoy a ground-truth status since they are inherent to neural communication, and indeed, many of the classical electrical recording techniques have been used alongside a separate optical stimulation device. The proximity of the light sources and the recording electrodes gives rise to two distinct types of artifacts like photovoltaic artifacts, and electromagnetic artifacts, which resemble spontaneous neural activity and hinders the interpretation of the recorded data.
