Dynamic mechanism of epileptic seizures induced by excitatory pyramidal neuronal population

The pyramidal neuronal population (PY) in the cerebral cortex is closely related to epilepsy, while the excitability of PY is directly affected by the excitatory interneurons (EIN), the inhibitory interneurons (IN), and the thalamic relay nucleus (TC). Based on this, we use the thalamocortical neural field model to explore the dynamic mechanism of system transition by taking the synaptic connection strengths of the above three nuclei on PY as the main factor affecting seizures. The results show that the excitatory effects of EIN on PY induce transitions from 1-spike and wave discharges (SWDs) to 2-spike and wave discharges (2-SWDs), the inhibitory effects of IN on PY induce transitions from saturated state to tonic oscillation state, and the excitatory effects of TC on PY induce transitions from clonic oscillation state to saturated state. According to the single-parameter bifurcation analysis, it is found that Hopf and fold limit cycle bifurcations are the key factors leading to the state transition. In addition, the state analysis of the three pathways is carried out in pairs. The results show that the system produces more types of epileptic seizures with the combined action of EIN and TC on PY. According to the two-parameter bifurcation curve, we obtain the stable parameter areas of tonic-clonic oscillations, SWDs, 2-SWDs and saturated discharges, and clearly find the reasonable transition path between tonic-clonic seizures and absence seizures. This may provide some theoretical guidance for the transmission and evolution of seizures.