The Virtual Reality Servo Ball is a novel virtual reality experimental system. It is based on an active, servo driven spherical treadmill. It allows a freely moving rodent (mouse, rat) to navigate in virtual space. Virtual reality provides a perfectly controllable experimental environment. It can be used for investigating navigation, cognition, learning and memory. Freely moving animals can be examined during unrestrained behaviour or through electro - or opto-physiological methods, telemetry or pharmacological interventions while the animal performs complex behaviours. A large range of brain circuits can be stimulated through multi-modal
stimulation. The available sensory modalities include visual, acoustic, tactile and olfactory stimuli. Reinforcement feedback can be given through positive (sugar water) or negative (air puff) reinforcement. Operant behaviour and emotional responses can be examined. For unrestrained animals even 24-hour experimentation is possible. Automated experimentation with multiple individuals is possible. This is achieved through a tube access system to the animals' home cage. Animals can be given individual access from their home cage to the Virtual Reality Servo Ball through the optional automated ID-Sorter and electronic gates.