One of the basic prerequisites of our aim to develop neurotechnological devices is to identify optimal strategies with respect to where, when, and how to interact with the brain. Ultimately, this interaction will be bi-directional, as we want both to “read out” information as well as to “write in” commands in the brain to induce favourable changes of activity in neuronal networks. Before linking “write-in” and “read-out” in one system, we follow a uni-directional approach as the establishment of a working communication in either direction can be pursued on several levels of complexity and description. One can focus on small local circuits, but also try to cover networks of large-scale populations that spread across multiple brain areas. Research area A forms the framework needed to match the hierarchies that we observe on the anatomical, functional, and signal level. This is required to relate the biological foundations to clinically relevant neurological states – which in turn enables us both to modify them where they induce neurological disorders, and on the other hand to use neuronal activity as a source of information for the control of brain-machine interfaces. Towards these goals, we use a range of approaches and techniques, from the modelling of networks to functional magnetic resonance imaging (fMRI), electrophysiology and optogenetic tools to interact with networks. In vitro models, networks of living nerve cells in petri dishes, as well as and ex vivo approaches, e.g. brain slices, serve as test beds for fundamental questions and approaches. We further use in vivo experiments in animals to identify functional networks and interact with them. This is done in healthy as well pathological states – carried out in close collaboration with research area C. Finally, a task of this research area is to validate predictions, and to test new technical developments that are made in research area B.