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With the increasing application of imaging techniques, characteristic changes in the structure and functional activity of certain neuronal networks and transmitter Systems have been discovered in the brains of patients suffering from various psychiatric disorders. These findings have often been assumed to support biological concepts of the genetic background and causation of these disorders. However, several lines of research are converging to indicate that the initially established genetically programmed neuronal Connectivity is further elaborated, fine tuned and modified by usedependent neuronal and synaptic plasticity. In all socially organized species in general and in human subjects in particular, psychosocial experiences appear to represent the most important trigger of use-dependent adjustments of neuronal Connectivity through the facilitation, modification and reorganization of neuronal networks. In experimental animals, changes in psychosocial rearing conditions were shown to cause profound and persistent changes in the cytoarchitecture, dendritic arborization and synapse formation in individual brain regions as well as in the maturation of monoaminergic afferences. Based on these findings, the mechanisms of the biological affixation of psychosocial experiences are described and the implications of experience dependent neuronal and synaptic plasticity in the prevention and the therapy of mental disorders are outlined.