Uncovering the Correlation Between Spindle and Ripple Dynamics and Synaptic Connections in a Hippocampal-Thalamic-Cortical Model

Consolidation of new information in memory occurs through the simultaneous occurrence of sharp-wave ripples (SWR) in the hippocampus network, fast–slow spindles in the thalamus network, and up and down oscillations in the cortex network during sleep. Previous studies have investigated the influential and active role of spindles and sharp-wave ripples in memory consolidation. However, a detailed investigation of the effect of membrane voltage of neurons and synaptic connections between neurons in the cortex, hippocampus, and thalamus networks to create spindle and SWR is required. This paper studies the dynamic behaviors of a hippocampal-thalamic-cortical network as a function of synaptic connection between excitatory neurons, inhibitory neurons (in the hippocampus and cortex), reticular neurons, and thalamocortical neurons (in the thalamic network). The bifurcation diagrams of the hippocampus, cortex, and thalamus networks are obtained by varying the strengths of different synaptic connections. The power diagrams for SWR and sleep spindles are shown accordingly. The results show that variations in synaptic self-connection (and inhibitory synaptic connection) of excitatory neurons in the CA3 region, as well as synaptic connection between excitatory neurons from CA1 region to excitatory neurons (and inhibitory neurons) in the cortex network have the most significant influence on dynamical behavior of the network. Furthermore, comparing diagrams for different synaptic connections shows that SWR is formed by excitatory neurons in CA3 region of the hippocampal network, passes through CA1 region, and enters cortex network.