Brain's theta oscillators achieve flexible phase-locking via multi-timescale inhibition

A new study from Wang and Pittman-Polletta (arXiv 2605.08014) uncovers the dynamical mechanisms behind the brain's ability to phase-lock to rhythmic speech inputs over a wide range of timescales. The researchers used a biophysically grounded cortical theta oscillator model and tools from dynamical systems theory to show that interactions between inhibitory currents operating on multiple timescales enable this flexibility.

Specifically, they found that a theta-timescale (4–8 Hz) inhibitory current (I_m) and a slower delta-timescale (1–4 Hz) potassium current (I_KSS) cooperate to create a three-timescale structure. This interaction gives rise to a delayed Hopf bifurcation phenomenon, which introduces prolonged post-input recovery delays. Interestingly, the superslow I_KSS current plays little role in unforced oscillations but becomes critical under external rhythmic forcing, expanding the phase-locking range. The intermediate I_m current further extends this range by prolonging recovery along the superslow manifold. These results suggest that coordination among multiple inhibitory currents is a key mechanism for flexible speech rhythm tracking in the brain, with potential implications for understanding auditory processing disorders and designing biologically inspired audio processing systems.