The brain depends on precisely timed neuronal activity to control behavior. In the hippocampus, neurons fire in-sync with theta oscillations – rhythmic brain waves occurring at about 5 to 12 times per second — creating windows of time in which neurons can work together to drive cognition. Inhibitory neurons are especially tightly locked to this rhythm, helping route information and keeping excitation and inhibition in balance. However, most of what we know about the function of this precise spike timing comes from correlation, inferred from symptoms of diseases where it breaks down. Our lab works to directly manipulate neural timing to uncover how small disruptions in spike timing cause cognitive impairment and seizures, and how restoring proper timing can rescue function. Using closed-loop systems, we test how the synchrony of inhibitory neurons shapes plasticity and cognition, both in the healthy brain and in the context of epilepsy and aging.