Inhibitory Network Bistability Explains Increased Interneuronal Activity Prior to Seizure Onset

Area of Science:

• Neuroscience
• Computational Neuroscience
• Systems Neuroscience

Background:

• GABAergic interneurons show increased, synchronous activity before seizure onset.
• This pre-ictal interneuron activity may causally drive seizure initiation.
• Mechanisms for this increased activity without permanent input changes are unknown.

Purpose of the Study:

• Investigate mechanisms predisposing inhibitory networks to increased activity before seizures.
• Model the role of hyperexcitable interneurons in pre-ictal dynamics.
• Explain the abrupt transition to synchronous firing observed experimentally.

Main Methods:

• Simulated inhibitory networks with control and hyperexcitable interneurons (modeled with 4-Aminopyridine).
• Compared network dynamics and propensity for abrupt transitions to synchrony.
• Investigated the role of brief perturbations and background excitatory activity.

Main Results:

• Networks with hyperexcitable interneurons are more prone to a bistable state.
• Asynchronous firing networks can abruptly transition to synchrony upon perturbation.
• This transition increases overall firing rate and can be driven by cortical excitatory activity.

Conclusions:

• Bistability in inhibitory networks explains increased interneuron activity before seizures via a transition from incoherent to coherent dynamics.
• Hyperexcitable interneurons increase vulnerability to this dynamic shift, enabling transitions without permanent input changes.
• This computational model generates testable hypotheses for inhibitory neuron roles in pre-ictal neural dynamics.