The main physiological function of the hippocampus is the processing of episodic memory. Neuronal plasticity, involved in the strengthening and weakening of synapses, constitutes the mechanism by which this function is accomplished.
As the hippocampus is involved in the autobiographical part of memory, it can be expected as being involved in psychiatric diseases. Neuronal plasticity is affected in many pathological situations in which stressor procedures are involved, such as depression, schizophrenia and Alzheimer’s disease, and also post-traumatic stress disorder (PSTD), a characteristic disease in which organic disturbances are induced by a specific external event. Many theories have been developed about the pathogenic mechanisms of these diseases, but neuronal plasticity is affected in all, irrespective of their basic causes, which are largely unknown. This review provides a combined-composite approach to the main psychiatric diseases, concluding in their common ways of expression, according to research findings. Gradually, common pathways have been revealed in the pathophysiology of the above diseases, associated with synaptic function. The shrinkage of the hippocampus is a common finding, with some exceptions. Reduction in the density of the dendritic network also constitutes a common finding. This leads to a decrease in the total synaptic surface, indicating that along with reduction in hippocampal volume, synaptic function is impaired. Despite progress in understanding the neurophysiology and neuropathology, the precise connection between research findings and clinical manifestations is lacking. Further pathophysiological steps need to be explored to reveal a cause-effect relationship, in order to explain the common findings and variety in manifestation of these diseases.