Intrinsic and synaptic dynamics interact to generate emergent patterns of rhythmic bursting in thalamocortical neurons

Rhythmic inhibition entrains the firing of excitatory neurons during oscillations throughout the brain. Previous work has suggested that the strength and duration of inhibitory input determines the synchrony and period, respectively, of these oscillations. In particular, sleep spindles result from a cycle of events including rhythmic inhibition and rebound bursts in thalamocortical (TC) neurons, and slowing and strengthening this inhibitory input may transform spindles into spike- wave discharges characteristic of absence epilepsy. Here, we used dynamic clamp to inject TC neurons with spindle- like trains of IPSCs and studied how modest changes in the amplitude and/ or duration of these IPSCs affected the responses of the TC neurons. Contrary to our expectations, we found that prolonging IPSCs accelerates postinhibitory rebound (PIR) in TC neurons, and that increasing either the amplitude or duration of IPSCs desynchronizes PIR activity in a population of TC cells. Tonic injection of hyperpolarizing or depolarizing current dramatically alters the timing and synchrony of PIR. These results demonstrate that rhythmic PIR activity is an emergent property of interactions between intrinsic and synaptic currents, not just a passive reflection of incoming synaptic inhibition.