A fast and flexible panoramic virtual reality system for behavioural and electrophysiological experiments

Abstract

Ideally, neuronal functions would be studied by performing experiments with unconstrained animals whilst they behave in their natural environment. Although this is not feasible currently for most animal models, one can mimic the natural environment in the laboratory by using a virtual reality (VR) environment. Here we present a novel VR system based upon a spherical projection of computer generated images using a modified commercial data projector with an add-on fish-eye lens. This system provides equidistant visual stimulation with extensive coverage of the visual field, high spatio-temporal resolution and flexible stimulus generation using a standard computer. It also includes a track-ball system for closed-loop behavioural experiments with walking animals. We present a detailed description of the system and characterize it thoroughly. Finally, we demonstrate the VR system’s performance whilst operating in closed-loop conditions by showing the movement trajectories of the cockroaches during exploratory behaviour in a VR forest.

Cockroach optomotor responses below single photon level

“…The unattenuated light intensity of the optomotor stimulus pattern from the projector (DepthQ ® , Lightspeed Design, Bellevue, Washington, USA) reflecting via the projection surface, as measured in the centre of the sphere, was 500 lx. The spectrum of a full-field image at 100% brightness peaks at approximately 440, 550 and 575 nm (Takalo et al, 2012). Lower light intensities were created by placing −2, −4, −5 and −6 decade neutral density filters (NE Series, Thorlabs, Newton, New Jersey, USA) in front of the projector lens.…”

“…Similar results have been obtained previously in flies (Dubs et al, 1981;Scholes and Reichardt, 1969), but we are confident that our use of identical stimuli in both behavioural and electrophysiological experiments, along with the use of the spherical VR setup, gives more reliable results. All our recordings were made from green-sensitive photoreceptors, because the projector used in the VR setup did not emit ultraviolet (Takalo et al, 2012). First, 500 lx high-intensity stimuli were used to characterize photoreceptor light responses under VR settings.…”

“…We used a VR setup, described previously (Takalo et al, 2012), in the openloop mode. The stimulus was a grating of vertical black and white bars with ; n, number of cells analyzed.…”

“…We were able to overcome this problem with a panoramic virtual reality (VR) system (Takalo et al, 2012) that was fitted with a trackball. Carefully positioning the cockroach on the trackball could eliminate inputs from the antennae and mouthparts, and create conditions under which it was constantly motivated to walk under visual stimulation (Fig.…”

Insects modify their behaviour depending on the feedback sensor used when walking on a trackball in virtual-reality

“…Closed-loop paradigms, which simulate free untethered motion, measure the tethered animal's motor output and concurrently use this to update the animal's sensory environment, permitting a careful study of the interaction of the animal with its environment (Taylor et al, 2008). A useful experimental paradigm to study the behaviour of walking animals is to place them on an air-supported trackball, where the ball's movements in reaction to an animal's leg movements are measured and used to change its sensory environment (Harvey et al, 2009;Seelig et al, 2010;Takalo et al, 2012).…”