Theta-frequency bursting and resonance in cerebellar granule cells: Experimental evidence and modeling of a slow K+-dependent mechanism

Neurons process information in a highly nonlinear manner, generating oscill ations, bursting, and resonance, enhancing responsiveness at preferential f requencies. It has been proposed that slow repolarizing currents could be r esponsible for both oscillation/burst termination and for high-pass filteri ng that causes resonance (Hutcheon and Yarom, 2000). However, different mec hanisms, including electrotonic effects (Mainen and Sejinowski, 1996), the expression of resurgent currents (Raman and Bean, 1997), and network feedba ck, may also be important. In this study we report theta-frequency (3-12 Hz ) bursting and resonance in rat cerebellar granule cells and show that thes e neurons express a previously unidentified slow repolarizing K+ current (I K-slow). Our experimental and modeling results indicate that IK-slow was ne cessary for both bursting and resonance. A persistent (and potentially a re surgent) Na+ current exerted complex amplifying actions on bursting and res onance, whereas electrotonic effects were excluded by the compact structure of the granule cell. Theta-frequency bursting and resonance in granule cel ls may play an important role in determining synchronization, rhythmicity, and learning in the cerebellum.