[Theoretical and clinical significance of neuroplasticity]

Plasticity is a specific feature of the nervous system, characterized by two basic phenomena: The first type of "functional plasticity" develops comparatively quickly, brings about mainly functional changes and is usually reversible. The second type has the features of an adaptation and affects the expression of genotype into phenotype. Neuroplastic mechanisms are triggered by various natural or artificial stimuli which may differ quantitatively (they arise in the internal or external environment) or qualitatively. Neuroplastic mechanisms are based on modulation of the signal transmission over synapses (e.g., the transmitter release, activity of postsynaptic receptors, efficiency changes in the transmission in the postsynaptic segment). They can be related to the interneuronal relations changes (e.g., number of certain types of synapses, significance of the wiring of different elements of the neuronal circuits). Resulting changes may occur in the communication between neurons (synaptic level), in the activity of the local neuronal circuits (level of local circuits) or in the relations between individual functional brain systems (multimodular level). Neuroplasticity might be based on structural changes which can be revealed by morphological methods. Such forms of plasticity are more frequent during the development, or as a reaction to injury (proliferation and decease of neurons, formation of their processes and spines, remodelling, or formation of synapses). More specific methods have determined that these changes are located on the molecular level (enzyme activity, production and release of transmitters or modulators, receptor activation, modulation of ion channels). Both levels of neuroplastic mechanisms bring about changes of functional parameters of the synaptic transmission (changes in the duration or amplitude of the membrane potentials and resulting facilitation, posttetanic potentiation or changes of opposite character). Effects of plasticity can reside either in positive or negative changes during the development (evolutional plasticity), after a short-term exposition (reactive plasticity), after long-term or permanent stimuli (adaptational plasticity), and during functional or structural recovery of the damaged neuronal circuits (reparation plasticity). Manifestations of plasticity have probably the same basis, irrespectively of the cause which has triggered them, or the brain region where they have been accomplished. (Tab. 7, Ref. 45.)