He has published 42 manuscripts in peer-reviewed journals and has received over 1000 career citations, h-index = 19). He completed his PhD on the neural and behavioural effects of cannabinoids (cannabis-like drugs) under Professor Iain McGregor at the University of Sydney in 2001. During his PhD Dr Arnold became fascinated by how genetic disposition influences the neurobehavioural actions of cannabinoids - understanding which genes affect cannabinoid action might help explain why certain individuals are more prone to mental disorders such as addiction or schizophrenia.