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The aim of this study is to examine and assess a number of recently developed possibilities for intervening in the central nervous system (CNS), in particular the brain. Most of these possibilities have been opened up by innovative biomedical technologies. This is certainly true for the field of central neural prostheses covering various kinds of electronic devices which connect to the CNS in order to either influence (stimulate or inhibit) or record neural activity. The entire spectrum of technologies in this field — from electronic implants for the restoration of lost sensory function to brain-computer/machine-interfaces for the “mental” control of motor prostheses which are primarily meant to compensate for physical disabilities — is explored in Chapter 3.

Fantasies of intervening in the psyche and the use of psychotropic agents have a venerable history in mankind. Even in prehistoric times, substances like opium, cannabis, coca, peyote and alcohol were used, especially in the context of religious and magic rituals and other cultural practices. In ancient Greece, for example in the Hippocratic writings and the writings of Dioscourides and Galen, the use of opium was recommended for the treatment of pain and sleep disorders, particularly in women. Helleborus was the treatment of choice in psychiatric diseases. The Greek authors distinguished the black helleborus, a purgative, from the white helleborus, a substance which induced vomiting. Ancient Greek medical writings show that doctors believed psychiatric illnesses to have somatic foundations. They therefore tried to heal through the extraction of illness-inducing substances using emetics or purgatives. As can be seen, the concept of the so-called “biological psychiatry”, meaning physical interventions in the psyche through somatic changes by means of pharmaceutical agents or other manipulations with an impact on the human brain, is a very old one. In the Middle Ages in Europe, cathartic methods using purgatives, emetics or phlebotomy retained some of their importance whilst different herbal extracts of plants with greater or lesser toxicity gained ascendance in the monastic medicine. Women collecting these plants and having some knowledge about their therapeutic effects often risked to be accused of witchcraft.

Research on the nervous system has been intensified over the last decades and still is booming. Basic neuroscience has dramatically increased the knowledge of cellular and molecular mechanisms of brain functioning. As a result cellular and molecular disarrangements that go with the variety of neurological, neurodegenerative and psychiatric disorders have been identified, although the primary causes of these disorders remain largely unknown. In cases of acquired or degenerative loss of nervous functions, pharmacological treatments are still mainly directed towards the amelioration of symptoms and the limitation of secondary tissue damage. This clinical problem together with the development of new potential therapeutic techniques such as cell grafting or implantation and gene transfer, have led to the exploration of interventions in the nervous system that can tentatively be called “restorative neurosurgery”. A shift from animal experimentation to clinical trials occurred rapidly and experimental neurotransplantation surgery in patients with neurological and neurodegenerative disorders has taken place over several decades. Neuroscience, however, is just beginning to explore cellular and molecular interventions in diseased, degenerating or traumatised human nervous systems. Are we approaching an era of interventions in the brain that will revolutionise treatment of thus far untreatable brain disorders?

The nervous system is one of the most influential human physiological systems. Virtually every organ in the human body is contacted by a nerve. Most bodily functions are under neural control or modulated by neural activity. This is the reason why any loss of neural function may cause deleterious impairment of health.

During the past decades focal high frequency electrical stimulation of the human brain has been used in order to treat the symptoms of several neurological disorders, including Parkinson’s disease, essential tremor, dystonia, epilepsy and Tourette’s syndrome. In the human brain neuronal circuitries have been detected which are responsible for motor control, others enable reception of information from the different sense organs (vision, hearing, sensation, taste, smell), still others are responsible for emotion, sexual behaviour, intelligence, memory etc. These circuitries do not simply exist in parallel to one another. Rather, there exist important connections in between them. Transmission of information runs via action potentials within one neuron and via neurotransmitters being released at the synapses in between neurons. Action potentials are transient electrical depolarisations of the cell membrane which propagate the signal from one place to another in the cell. Technically, it is possible to intervene with the electrical activity of a neuron by simply administering in the neighbourhood of that neuron an electrical field, which changes over time at a frequency in clinical practice usually between about 50 to 180 Hz (figure 4.1). In patients, this treatment is performed by means of implanting an electrode in a certain area of the brain. The electrode can be connected to an extension cable and an external current source.

It was mentioned in the introduction that one of the major types of concerns related to new methods of intervening in the brain is expressed in the question whether the identity of those persons they are applied to is put at risk. Worries of this kind have already been voiced in the past with respect to traditional intervention techniques used in neurosurgery, psychopharmacology, and even (non-invasive) psychotherapy. However, the availability of new techniques like neural grafting, neuroprosthetics and electrical brain stimulation endows those old concerns with new socio-political vigour.^22 In this preliminary section we will attempt to disambiguate the fears of those who would regard certain techniques for intervening in the brain as a potential threat to personal identity. In doing so, it will turn out that, while some particular worries falling within this category need not be dealt with at great length, others require a clarification of the concepts of identity in general, of personal identity in particular, and of related concepts like personhood and personality before a comprehensible assessment of possible hazards can be given for different techniques.

As far as the considerations in the present chapter deal with questions of law, it is not their purpose to analyse these questions from the perspective of a particular legal order (or of several such orders). Rather, what they aim at is to clarify the problems according to basic principles of law. On rare occasions, though, we will demonstrate certain fundamental normative structures by exemplarily referring to the specific situation in German law. This does not, however, diminish our claim to present a principled, rather than a positivistic, legal analysis.

The history of therapeutic interventions in the psyche is as old as the history of medicine. Ancient Egyptian, Chinese and Greek medicine already included prescriptions for the treatment of what would nowadays be called “mental illness” (Millon 2004). Similarly, beyond the realm of therapy mankind has always sought means to enhance and develop features of the mind, as is evidenced by varied traditions of religious and spiritual practices. It is important to bear this historical perspective in mind when commenting on the concerns raised by recent methods of intervention in the central nervous system (CNS) which, in addition to providing new opportunities for treating and enhancing the psyche, may have inadvertent effects on the mental level as well.

Die Geschichte therapeutischer Eingriffe in die Psyche ist so alt wie die überlieferte Geschichte der Medizin selbst. Bereits die altägyptische, die traditionelle chinesische und die antike griechische Medizin enthielten Vorschriften zur Behandlung von Krankheiten, die heute als „psychische“ aufgefasst werden (Millon 2004). Doch auch jenseits dessen, was als Therapie galt, hat die Menschheit schon immer nach Möglichkeiten gesucht, psychische Fähigkeiten und Zustände zu verbessern oder zu erweitern, was insbesondere durch die vielfältigen Traditionen religiöser und spiritueller Praktiken belegt wird. Diese historische Perspektive sollte nicht vergessen werden, wenn man sich mit einigen prinzipiellen Bedenken befasst, denen zufolge die neuartigen Methoden des Eingreifens in das zentrale Nervensystem nicht nur neue Möglichkeiten für Behandlung und Enhancement 303 der Psyche eröffnen, sondern auch unerwünschte Wirkungen auf mentaler Ebene haben können.