The "neurosciences" is now a common 'term to describe several branches
of the biology related to studies of the nervous system. In fact, this
term also character- izes a multidisciplinary approach to studies of
probably the most complicated system of the most complicated living
organisms. Investigation of the central ner- vous system (CNS) is the
most quickly developing branch of the neurosciences. According to
Konorski's definition, the CNS "is endowed with two principal properties
which are referred to as reactivity and plasticity. Reactivity of the
sys- tem is its capacity to be activated by stimulation of receptive
organs; plasticity is the capacity to change its reactive properties as
the result of successive activa- tions" ([520], p. 7). According to
Kostyuk [535], plastic reorganizations include "any changes in the
efficacy or direction of neuronal connectivity which exceed in their
duration usual synaptic and spike events" ([535], p. 25). Neuronal
plasticity underlies adaptive modifications of various complexities both
in normal CNS, e. g. its development, formation of memory traces and
condi- tioned responses (CRs), as well as in brain pathology, e. g.
reorganization and compensation of damaged nervous functions.
Clarification of plasticity mecha- nisms is of great cognitive
importance and might be of practical value in the treatment of mental
and especially memory disorders.