Transcranial magnetic stimulation (TMS) can non-invasively activate neurons in the brain, which is useful for both brain research and clinical applications. A limitation of the method is that the activated neurons are hidden beneath the scalp and skull. Therefore, it is difficult to determine which neurons are actually activated by stimulation, which limits the potential of TMS in the diagnosis of brain disorders and brain research. In this project, we will develop a new method, transcranial magnetic fingerprinting (TMF), that is based on physical computer modelling and allows the quantification of several characteristics of the activated neurons, including their location, direction, and sensitivity. TMF enables a new non-invasive way to investigate the function and structure of the brain, their inter-individual variations and pathological alterations. Detailed quantitative information of the brain physiology can enable new indicators of brain disorders.