Introduction

The opto-quad is an enclosed arena that can accommodate groups of fruit flies that express optogenetic effectors in neurons in their brains. It consists of two glass panels sandwiched between 3D-printed parts. The lighting is provided by an 8x8 matrix of individually addressable WS2812B LEDs. The matrix is controlled by an Arduino, which allows certain parts of the arena to be lit and others to be dark. The flies are free to move between light and dark areas. Their preference for one over the other gives an idea of what effect activating(or inactivating) a neuron has. For example, if a rewarding neuron has an activating light-gated channel, like Chrimson, then the flies will prefer the lit side because that will be rewarding for them. Conversely, if a similar channel is expressed in a pain-sensing neuron, the flies will avoid the lit side as straying into the lit side would activate the neuron and create a sensation of pain. The device is similar in concept to other optogenetic devices built in the lab that are based on the WS2812B LEDs.