  Beta oscillations observed in motor cortical local field potentials (LFPs)
recorded on separate electrodes of a multi-electrode array have been shown to
exhibit non-zero phase shifts that organize into a planar wave propagation.
Here, we generalize this concept by introducing additional classes of patterns
that fully describe the spatial organization of beta oscillations. During a
delayed reach-to-grasp task in monkey primary motor and dorsal premotor
cortices we distinguish planar, synchronized, random, circular, and radial
phase patterns. We observe that specific patterns correlate with the beta
amplitude (envelope). In particular, wave propagation accelerates with growing
amplitude, and culminates at maximum amplitude in a synchronized pattern.
Furthermore, the occurrence probability of a particular pattern is modulated
with behavioral epochs: Planar waves and synchronized patterns are more present
during movement preparation where beta amplitudes are large, whereas random
phase patterns are dominant during movement execution where beta amplitudes are
small.
