SYNAPTIC PLASTICITY IN HIPPOCAMPUS INDUCE D BY THETA-LIKE PATTERN OF AFFERENT STIMULATION

The data are reviewed concerning synaptic plasticity of the hippocampa l monosynaptic pathways evoked by afferent activation which simulates activity of neurons in theta-rhythm, Activation with short high-freque ncy bursts applied with 5 Hz frequency effectively unduces long-term p otentiation. In contrast, activation with single pulses at 5 Hz causes the depontentiation or even long-term depression of the activated syn apses, ''in-phase'' activation of two afferent pathways in the theta-r hythm induces long-term potentiation, while the ''out-of-phase'' activ ation induces long-term depression of a ''weak'' pathway, A train of 3 0-50 pulses at 5 Hz evokes heterosynaptic short-term depression, i.e., a suppression of all synaptic inputs for 1 min, So-called ''hidden'' plasticity (the enhancement of the effect of delayed activation in pro ducing long-term depression) is also effectively evoked by the theta-l ike activatory patterns, Therefore, practically all known types of syn aptic plasticity can be effectively evoked by the afferent activation which reproduce the pattern of the hippocampal theta-rhythm, These phe nomena can underlie the theta-rhythm participation in learning and mem ory.