The present invention relates to a computer implemented system for animating a virtual object or digital entity. It has particular relevance to animation using biologically based models, or behavioural models particularly neurobehavioural models. There is provided a plurality of modules having a computational element and a graphical element. The modules are arranged in a required structure and have at least one variable and being associated with at least one connector. The connectors link variables between modules across the structure, and the modules together provide a neurobehavioural model. There is also provided a method of controlling a digital entity in response to an external stimulus.