[The effects of the social environment on the brain].

Aims: This work analyses the main studies dealing with the mechanisms by which the brain is altered by chronic stress and the impact of social stimuli on the activation of these mechanisms, which can lead to behavioural disorders and cognitive impairment in communities of mammals.
Development: The physiological and hormonal responses triggered as a response to stress are linked to alterations in certain areas of the brain and more particularly in the hippocampus. These mechanisms include hyperactivity of the hypothalamus-pituitary-adrenal axis, raised levels of corticosteroids and excitatory amino acids, neurotoxicity due to intracellular accumulation of calcium, apoptosis and a number of factors having to do with the immunological system. Most of these studies have involved the exogenous application of supraphysiological levels of corticosteroids or challenging the individual with stimuli that do not properly belong to their natural surroundings. Nevertheless, it is also possible that these mechanisms are triggered by aversive social stimuli from the natural environment, such as confrontation, establishing hierarchies, neglect and social evaluation. It has been proved that social stress has important effects on conduct and health, especially with regard to the structural and functional integrity of the brain.
Conclusions: Social stress can trigger important alterations in the nervous system of individuals exposed to it and these changes can manifest themselves as varying types of disorders affecting conduct and the cognitive skills. Nevertheless, not all natural surroundings give rise to these adverse effects, as balanced communities offer their members support, protection and a series of other advantages.