PiVR: an affordable and versatile closed-loop platform to study unrestrained sensorimotor behavior

Tools enabling closed-loop experiments are crucial to delineate causal
relationships between the activity of genetically-labeled neurons and
specific behaviors. We developed the Raspberry Pi Virtual Reality system
(PiVR) to conduct closed-loop optogenetic stimulation of neural functions
in unrestrained animals. PiVR is an experimental platform that operates at
high-temporal resolution (70 Hz) with low latencies (<30 ms), while
being affordable (<$500) and easy to build (<6 hours).
Through extensive documentation, this tool was designed to be accessible
to a wide public, from high-school students to professional researchers
studying systems neuroscience. We illustrate the functionality of PiVR by
focusing on sensory navigation in response to gradients of chemicals
(chemotaxis) and light (phototaxis). We show how Drosophila flies perform
negative chemotaxis by modulating their locomotor speed to avoid locations
associated with optogenetically-evoked bitter taste. In Drosophila larvae,
we use innate positive chemotaxis to compare behavior elicited by real-
and virtual-odor gradients. Finally, we examine how positive phototaxis
emerges in zebrafish larvae from the modulation of turning maneuvers to
orient in virtual white-light gradients. Besides its application to study
chemotaxis and phototaxis, PiVR is a versatile tool designed to bolster
efforts to map and to functionally characterize neural circuits.