Klaas Enno Stephan is a computational neuroscientist and medical doctor. His track record includes the development of the connectivity database CoCoMac (with Rolf Kötter), development of dynamic causal models of neuroimaging data and Bayesian model selection techniques (with Karl Friston and Will Penny), numerous studies of brain function and cognition in health and disease, and theoretical work on disease mechanisms in schizophrenia (the dysconnection hypothesis, with Karl Friston). His present work focuses on developing “computational assays”, i.e., mathematical models for inferring mechanisms of mental diseases from non-invasive brain activity measurements in individual patients. The hope is that such assays will support more precise diagnostics and individualized treatment recommendations, facilitating a redefinition of mental diseases and supporting a transformation of clinical practice. A particular emphasis is on brain-body interactions, examining how neuronal circuits and their plasticity are modulated by metabolic and inflammatory factors.