Beliefs and the brain.

our senses; they rest on four main types of proof demonstration: rational or inductive proof (‘I believe in what I see.’); scientific (deductive or experimental) proof; custom (which may lead to progressive acceptance of novel ideas, art, etc.); and intuition and revelation (including faith, either religious or non-religious). In medicine, the placebo effect and faith-associated healing [1, 2] belong mainly to the last of these mechanisms, while scientific beliefs , which rest on reproducible experiments, belong to ‘predictive thinking’, where room for doubt is supposed to remain (‘I believe that the sun will rise tomorrow morning, but I cannot be sure that this will happen.’). The realization that what were interpreted as scientific truths thirty or fifty years ago are now, in many cases, considered erroneous demonstrates the fragility of beliefs, even those seemingly supported by experimentation. In clinical research, randomized clinical trials are considered as the best examples of acquiring the most objective information on the efficacy of treatments. However, their interpretation does not escape the belief system and even constitutes good examples of scientific beliefs being introduced into medical practice, with two risks: the first is that their power of conviction is so strong that they transform into dogmas; the second is that they are not strong enough to counterbalance intuitive beliefs (either on the part of physicians or patients) in different, unproven treatments. By the way, the idea that experimentally established management is superior to intuWhile the ability to believe is an inherent feature of human thinking, it has virtually remained unstudied per se by modern neuroscience. A belief expresses mental acceptance of truth – the validity or reality of some thing – in the form of accepted adherence to a specific idea coexisting in a state of confidence and trust. Beliefs are so common in our lives that the term is often used synonymously with ‘thought’. Variants include dogmas , i.e. beliefs that are so well established that they have lost their identity as such – leading to a de facto exclusion of non-believers – and myths , which correspond to a belief in the symbolic value of something which is known not to be real. A belief serves the function of both representation (as of a concept) and justification (as for an act). Indeed, excluding the role of instinctive drives, without belief there is no action because there is no hope. Beliefs may become so intense that they pervade the being of an individual, as exemplified by religion and politics. While doubt tends to inhibit action, beliefs facilitate decision-making and subsequent acts, eliminating consideration of a wide range of solutions (‘I know what I must do.’). In fact, beliefs only make sense with reference to doubt (i.e. the possibility that a belief can be challenged), a concept that was developed by Descartes and his ‘cogito ergo sum ’ in the seventeenth century. Beliefs are established on the basis of the integration and acceptance of outer and inner perceptions through Received: April 1, 2007 Accepted: April 4, 2007 Published online: June 29, 2007