In this talk, I will introduce a current and holistic approach to brain functions. According to this theory, the brain ensures homeostasis with its environment by entertaining a model of the world. An idea which stems back to Helmholtz’s view of perception. In the last few years, this theory has gained a lot of interest in the field of computational neuroscience and is being more and more influential as (i) it guides the effort towards modeling brain functions, (ii) it sheds light onto recent empirical observations (e.g. from behavioral or neuroimaging studies), (iii) it provides insights on how to build adaptive machines and (iv) most importantly, it may lied to mechanistic accounts of brain dysfunctions; a mandatory step towards individualized diagnosis and treatments in neurological and psychiatric disorders. I will briefly illustrate some of these ongoing advances with concrete examples.