Miniaturized LED sources for in vivo optogenetic experimentation

Recently developed optogenetics techniques have enabled researchers to modulate the activity of specific cell types. As a result, complex neural pathways previously regarded as black boxes can now be directly probed, yielding a steadily increasing understanding of the basic neural circuits that underlie health and disease. For in vivo experimentation, fiber-coupled lasers have traditionally been used to illuminate internal brain regions, via an optical fiber that penetrates through overlying tissue. Though able to deliver intense fiber-coupled light, lasers are costly, bulky, and face limitations in output beam stability and temporal precision during modulated outputs. For experiments on unrestricted, behaving animals, a laser-based system also necessitates the use of fiber optic rotary joints, which come with costs and limitations of their own. Here, we report and characterize an alternative light delivery solution, based on high intensity fiber-coupled LEDs that are miniaturized for placement on the end of custom electrical commutators. This design allows for enhanced control of output light and expanded capabilities for optical stimulation as well as simultaneous electrical neural recordings, as with an optrode array. Temporal response of light outputs and light stability during commutator rotation were assessed. The influence of high current optical control signals on adjacent neural recording channels was also explored. To validate the function of this LED based system in in vivo recording scenarios, chronic stimulation experiments were performed.