Charlie Schroeder shows us the laminar profile of oscillations in cortex.  Different strengths for different frequency bands in different cortical layers.  Attention phase-synchronizes oscillations across layers facilitating communication between them. See Lakatos et al (2005) J. Neurophys.

Circuits from different thalamic nuclei  to cortex, one broad and modulatory, the other narrow and specific, may regulate oscillatory entrainment.

New Neuron paper shows cortical entrainment that matches periodic sensory inputs; phase depended on the attended frequency content., enhancing attended representations.  Lakatos et al 2013

Entrainment may explain cocktail party effect. Low frequency phase and high gamma power track attended speech.  Zion Golumbic et al