The opinion has been held that the same physiological mechanisms underlie the formation of long-term posttetanic potentiation (LTP) as underlie the preservation of the memory trace. An important role in the occurrence of LTP is assigned to changes in the ultrastructure and morphometric indices of the spinous synapses which govern the specific properties of their electrical reactions [3, 12]. The discovery of cytoskeleton proteins in the spines has made it possible to advance a hypothesis regarding the influence of cytoskeletal structures on the creation of the force stress which determines the form of spines [3, 11, 17, 19], as a result of which the cable properties of the spines and, simultaneously, the conductivity of the axospinous synapses may change [17, 18]. An attempt has been made to explain the phenomena of long-term posttetanic potentiation by the reorganization of proteins of the cytoskeleton in the presence of a change in the concentration of Ca 2§ in the spines as the result of prolonged activation of the synapse [4, 13]. The purpose of the present investigation was the study of the ultrastructural and morphometric changes taking place in the axospinous synapses immediately after electrical stimulation of surviving slices of the sensorimotor cortex of white mice, the identification of the most sensitive indices, as well as the ascertainment of the features of LTP in the sensorimotor cortex in parallel electrophysiological experiments carried out in an independant series under the same experimental conditions.