Coordination in Brain Systems

This chapter reviews the concept of dynamic coordination, its mechanistic implementation in brain circuits, and the extent to which dynamic coordination, and specific manifestations of it, have the power to account for functions performed by interacting brain systems. In our discussions, we addressed how on-the- y changes in coupling between neural subpopulations might enable the brain to handle the fast-changing recombination of processing elements thought to underlie cognition. Such changes in coupling should be apparent, rst and foremost, in the statistical relationship between activity in interconnected brain systems, rather than in the individual ring patterns of each subsystem. Dynamic coordination may manifest itself through a variety of mechanisms, of which oscillation-based synchronization is likely to play an important but not exclusive role. Also discussed is how modulation of phase relationships of oscillations in different brain systems, in neocortex and hippocampus of the mammalian brain, may change functional coupling, and how such changes may play a role in routing of signals at cross sections between cortical areas and hippocampal subdivisions. Possible mechanisms for oscillation-based synchronization, particularly in the gamma frequency range, are explored. It is acknowledged that the brain is likely capable of producing zero-phase lag between spatially dispersed cell populations by way of rather simple coupling mechanisms, primarily when neuronal groups are coupled symmetrically. Synchronization with remote areas may be most ef cient with phase differences that match the conduction delays. Fast-conducting, long-range projecting interneurons are identi ed as a potential substrate for synchronizing one neural circuit with another. A number of research strategies are identi ed to enhance our understanding of dynamic coordination of brain systems and how it might contribute to the implementation of the functions of those systems