Fries, P. (2005) A mechanism for cognitive dynamics: neuronal communication through neuronal coherence. Trends in Cogni- tive Science 9(10), 474-480. doi: 10.1016/j.tics.2005.08.011 1 Published in final edited form as: Trends in Cognitive Science 9(10), 474-480. doi: 10.1016/j.tics.2005.08.011 A mechanism for cognitive dynamics: neuronal communication through neu- ronal coherence Pascal Fries a, b a F.C. Donders Centre for Cognitive Neuroimaging, Radboud University Nijmegen, 6525 EN Nijmegen, The Netherlands b Department of Biophysics, Radboud University Nijmegen, 6525 EZ Nijmegen, The Nether- lands Corresponding author: F.C. Donders Centre for Cognitive Neuroimaging, Radboud University Nijmegen, 6525 EN Nijmegen, The Netherlands and Department of Biophysics, Radboud University Nijmegen, 6525 EZ Nijmegen, The Netherlands. Abstract: At any one moment, many neuronal groups in our brain are active. Microelectrode recordings have characterized the activation of single neurons and fMRI has unveiled brain- wide activation patterns. Now it is time to understand how the many active neuronal groups interact with each other and how their communication is flexibly modulated to bring about our cognitive dynamics. I hypothesize that neuronal communication is mechanistically sub- served by neuronal coherence. Activated neuronal groups oscillate and thereby undergo rhythmic excitability fluctuations that produce temporal windows for communication. Only coherently oscillating neuronal groups can interact effectively, because their communication windows for input and for output are open at the same times. Thus, a flexible pattern of co- herence defines a flexible communication structure, which subserves our cognitive flexibility.