Coherent rhythms may have other functions. One idea is that they provide a timing reference for a neural code that depends on the phase relationship of individual neurons with the reference oscillation. The stronger the excitation to an individual neuron, the earlier in the cycle it will fire. Thus neurons that fire at similar phases in the rhythm will have received similar intensities of input which may be used, for instance, to lock their outputs together for more effective summation. This hypothesis was proposed for hippocampal theta , and more recently for gamma .
1 Hopfield, J.J. Pattern recognition computation using action potential timing for stimulus representation, Nature, 376 (1995) 33-36.
2 O'Keefe, J. and Recce, M.L. Phase relationship between hippocampal place units and the EEG theta rhythm, Hippocampus, 3 (1993) 317-330.