The wealth of insights into the brain’s functioning neuroscience has gained during the last few decades led to the development of new possibilities for intervening in the brain: Central neural prostheses are electronic devices which connect to the nervous system in order to stimulate or record brain activity. Deep brain stimulation is administered by permanently implanted electrodes. Neurotransplantation offers a chance to treat degenerative diseases of the brain by replacing lost neurons. Although the primary aim of these innovative ways of acting on the brain is to open up new treatment options for neurological and psychiatric diseases, the public response to them has not been entirely positive. As regards therapy, there are concerns that these techniques may inflict severe mental harm on the patients they are applied to, possibly transforming them in radical ways. Further qualms relate to applications which may go "beyond therapy" by aiming at the enhancement of cognitive capacities and emotional well being. Both kinds of concerns have not only been raised with respect to novel neurosurgical procedures, but also regarding new trends in the field of psychopharmacology. Therefore, next to advances in the research areas of neuroprosthetics, neurotransplantation and electrical brain stimulation this study also covers more established ways of influencing brain activity and mental functioning respectively by means of pharmaceutical agents. The aim of this study is to review the state of the art with respect to each single mentioned kind of intervention, indicate future developments, and address the ethical and legal issues which are common to all of them.