A new paper in Cell measures theta waves in the hippocampus of rats navigating a maze with multiple spatial paths. They found a decision-making process seemed to be involved consistently with theta wave patterns. The paper itself requires a subscription or purchase but there is a good article on it in Quanta Magazine.
The hippocampus generated a representation of the left-turning choice during one cycle, then switched to the right-turning choice for the next one. The scenarios didn’t always alternate perfectly throughout the experiment — occasionally the same one would persist for a few cycles — but the structure in the signals was undeniable. The 125-millisecond sequences seemed to segregate the brain’s different hypotheses about the future into a continuous and consistent overall framework.
One could regard the brain waves themselves as incidental to the decision-making that is really being done by the brain circuits, but this association of brain waves with cognitive processes is what would be expected by EM field theories.