The engram formation and the global oscillations of CA3

Abstract

The investigation on the conditions which cause global population oscillatory activities in neural fields, originated some years ago with reference to a kinetic theory of neural systems, as been further deepened in this paper. In particular, the genesis of sharp waves and of some rhythmic activities, such as theta and gamma rhythms, of the hippocampal CA3 field, behaviorally important for their links to learning and memory, has been analyzed with more details. To this aim, the modeling-computational framework previously devised for the study of activities in large neural fields, has been enhanced in such a way that a greater number of biological features, extended dendritic trees—in particular, could be taken into account. By using that methodology, a two-dimensional model of the entire CA3 field has been described and its activity, as it results from the several external inputs impinging on it, has been simulated. As a consequence of these investigations, some hypotheses have been elaborated about the possible function of global oscillatory activities of neural populations of Hippocampus in the engram formation.

Appendix

The following values have been utilized for the basic neuronal parameters in the above reported computer simulations. The resting levels $e_{rs^{\prime}}$ of different neurons were: e _rp = 0.34 (corresponding to −75 mV)—pyramidal neurons, e _rf = 0.67 (corresponding to −62.5 mV)—fast inhibitory neurons, e _rs = 0.34 (corresponding to −75 mV)—slow inhibitory neurons. The periods of absolute refractoriness and the synaptic delays were: τ _p = 15 ms, τ _f = τ _s = 1.75 ms and t _0p = t _0f = t _0s = 0.5 ms, respectively. The slow-IPSP onset time had value $\bar{t}_{s} = 30\,{\rm ms}.$ The long-distance impulses in the absorption-free zone assumed a constant velocity v′ = 60 cm/s.