Significance Rhythmic brain activity is a signature of information processing. Common inhibitory cells, spike-frequency adapting interneurons, are typically thought to only participate in low-frequency rhythms (<10 Hz). However, we found that these cells’ frequency preference can be switched from 2 to 200 Hz. The switch occurs when low-frequency components dominate the interneurons’ input, as is the case during brain states of slow-wave sleep or quiet rest. These interneurons not only increase their sensitivity to input in the 30 to 200 Hz range (gamma and ripples) they do so within a few dozen milliseconds, in phase with the low-frequency input components. Our findings reveal unexpected flexibility in neurons, which could shape theta-gamma cross-frequency coupling, a phenomenon thought to contribute to information routing.