Zachary Mainen is a neuroscientist whose research focuses on the brain mechanisms of decision-making. He studied psychology and philosophy at Yale University, received his doctorate in Neuroscience from the University of California, San Diego, and held a faculty position at Cold Spring Harbor Laboratory, New York, before moving to Lisbon, Portugal in 2007 to found the Champalimaud Neuroscience Programme, where he was the Director between 2009-2014. In 2015, Mainen was named co-Director of Champalimaud Research, along with Dr. Rui Costa. His work has been recognised by two Advanced Investigator Grants of the European Research Council (2010 and 2015) and the election to the European Molecular Biology Organisation. Mainen’s research explores brain function, especially decision-making, using theory-driven experimental approaches. His laboratory helped to pioneer the use of quantitative behavioural paradigms in rodents and combines those approaches with electrophysiological, optical and genetic techniques to study neural representation and computation. He has a long-standing interest in the issue of how noise and uncertainty impact neural systems and behaviour and our understanding of these processes. His lab is currently exploring these questions in the context of odour-guided perceptual decisions and learning, the timing and selection of simple actions, and the role of the neuromodulator serotonin in behaviour and cortical function. This work touches on philosophical issues surrounding causality, free will, knowledge and belief.