Competing routes back to firing shape population hyperexcitability and its selective suppression

In whole-cell recordings of midbrain dopamine neurons, the subthreshold trough resolves a non-monotone firing hazard into distinct return pathways, including an early-return route and a sequestration route.

• Why it matters: Hyperexcitability depends on how neurons regain the opportunity to fire across the spike cycle, not only on whether quiescent cells can activate.
• What they did: The authors decompose the non-monotone aggregate firing hazard into physiologically distinguishable components and model them as competing return pathways in a population renewal framework.
• The result: An immediate-return pathway promotes population hyperexcitability independent of quiescent activation, while a sequestration pathway yields prolonged non-recruitable states; phenytoin and carbamazepine act by redistributing neurons among pathways.

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