FIGURE 4.

Cellular and network mechanisms of oscillatory encoding and modulation in the cortico-cerebello-cortical circuit. Panel labels are color-coded according to where in the circuit a modulation of the neuronal signal occurs, corresponding to the schematics in the top-center. (A) Cortico-cerebellar signals originate in the deep layers of the neocortex, where alpha and beta oscillations predominate. (B) Pre-cerebellar neurons in the pons translate a dynamic current input into rate in a linear fashion, thereby translating oscillatory current into a rate code. (C) Deep and superficial GCs respond preferentially to different phases of the ponto-cerebellar signal, thereby encoding both phase (via time) and amplitude (via GC depth) of oscillatory input. (D) Phase and phase difference of oscillatory activity is decoded by Purkinje cells, via two potential mechanisms. Top: tidal wave theory proposes that a phase difference in a band-limited frequency range can be calculated as a time difference along slow-conducting parallel fibers. Each parallel fiber conveys information about the phase of one cerebral oscillation, and together convey information about the phase relationship of their inputs. Two inputs offset by Δt would arrive simultaneously at the Purkinje cell dendritie. Bottom: simulations show that rhythmic excitation can generate network resonance across parallel fiber beams with a phase shift, due to cross-beam inhibition from MLIs. Rhythmic excitation could augment Purkinje cell responses to input across parallel fiber beams, thereby providing a means to calculate phase differences that are too great to be accounted for in parallel fiber conduction length. (E) Feedback to the cortex conveyed via thalamocortical projections. Multi-areal matrix-type projections target superficial and deep layers in multiple cortical areas, likely inducing simultaneous beta oscillations that facilitate simultaneous gamma bursts in targeted regions. Focal matrix-type projections preferentially target the superficial layers, suggesting a role in spatially selective augmentation of gamma responses during the bottom-up flow of information.