Functional characteristics of the principal intrinsic systems of hippocampal connections

By extracellular recording of unit activity and electrical stimulation of unanesthetized rabbits the character of the following principal intrinsic hippocampal connections was investigated: fascia dentata with area CA₃ (series FD-CA₃) and area CA₃ with area CA₁ (series CA₃-CA₁). Differences between the functional characteristics of these two systems of connections were shown. The CA₃-CA₁ system was highly efficient, with a sharply defined boundary between subthreshold and threshold intensities of stimulation and with a wide range of active frequencies; recruiting was negligible and no sign of prolonged potentiation was present. The FD-CA₃ system was characterized by low efficiency, a wide threshold zone, and narrow range of active frequencies, slow recruiting, and long preservation of incoming influences. The probability that these functional differences depend on the morphological characteristics of the systems of connections and their possible role in the function of the hippocampus are discussed.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 259–266, May–June, 1976.