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The hippocampal formation is crucial for learning and memory, with submodule CA3 thought to be the substrate of pattern completion. However, the underlying synaptic and computational mechanisms of this network are not well understood. Here, we perform circuit reconstruction of a CA3 module using three dimensional (3D) electron microscopy data and combine this with functional connectivity recordings and computational simulations to determine possible CA3 network mechanisms. Direct measurements of connectivity schemes with both physiological measurements and structural 3D EM revealed a high connectivity rate, multi-fold higher than previously assumed. Mathematical modelling indicated that such CA3 networks can robustly generate pattern completion and replay memory sequences. In conclusion, our data demonstrate that the connectivity scheme of the hippocampal submodule is well suited for efficient memory storage and retrieval. [ABSTRACT FROM AUTHOR]

The article focuses on the biophysical properties of voltage-gated sodium (Na+) and potassium (K+) channels in human and mouse pyramidal neurons and their impact on the stability of action potentials (APs) during sustained firing. Human pyramidal neurons exhibit stable and fast AP kinetics, attributed to more depolarized voltage dependence, slower inactivation, and faster recovery from inactivation of Na+ channels, as well as right-shifted activation and inactivation curves of K+ channels.

The article focuses on understanding the mechanisms underlying fast cortical signaling in human fast-spiking interneurons (FSINs). The study compares human and mouse FSINs, revealing that despite elongated dendrites in human FSINs, they maintain fast inhibition through adaptations such as stronger excitatory inputs, larger dendrite diameter with reduced complexity, faster action potential initiation, and faster and larger inhibitory output.