[The social brain: neurobiological bases of clinical interest]

Human social capacities are developmentally late and unique. They allow for a specialisation that enhances the availability of resources and facilitates reproduction. Our social complexity rests on specific circuits and mechanisms, which are analysed here.

The following are put into operation for those purposes: knowledge of the other by means of empathy, specific mechanisms that endow us with the capacity to detect defrauders, genetic and biochemical factors, and the autonomic nervous system. Empathy is the basic mechanism in sociability. It has different levels of complexity (emotional, cognitive, attribution), with specific anatomical differentiation. Social matters are linked to emotional ones, and this in turn to the homeostatic aspects. Hence, physical and social pain share an anatomical matrix and therapies. We are social beings of a selfish biological nature, which we adjust thanks to a special capacity to detect defrauders, which is dominant over those involving planning or abstraction. Oxytocin is the essential prosocial neurochemical mediator. Serotonin and the enzyme MAO are considered as having an antisocial capacity, which is dependent on the interaction with adverse environments. Finally, the vagal system, which is more recent phylogenetically speaking and myelinated, that of the dorsal nucleus of the vagus nerve, is a requirement for warm and leisurely social interaction.

The neurobiology of social matters makes it possible to recognise disorders affecting this behaviour in structural injuries (vascular, of the white matter, dementias, etc.), neurodevelopmental disorders (autism), psychiatric illnesses (schizophrenia) or personality disorders. There are a number of promising therapeutic interventions (transcranial magnetic stimulation, drugs). The addition of cultural and environmental factors to the neurobiological ones introduces a greater amount of ecological complexity, but without lessening the validity of what it outlined.