A general conceptual framework for large-scale neocortical dynamics based on data from many laboratories is applied to a variety of experimental designs, spatial scales, and brain states. Partly distinct, but interacting local processes (e.g., neural networks) arise from functional segregation. Global processes arise from functional integration and can facilitate (top down) synchronous activity in remote cell groups that function simultaneously at several different spatial scales. Simultaneous local processes may help drive (bottom up) macroscopic global dynamics observed with electroencephalography (EEG) or (...) magnetoencephalography (MEG). A local/global dynamic theory that is consistent with EEG data and the proposed conceptual framework is outlined. This theory is neutral about properties of neural networks embedded in macroscopic fields, but its global component makes several qualitative and semiquantitative predictions about EEG measures of traveling and standing wave phenomena. A more general “metatheory” suggests what large-scale quantitative theories of neocortical dynamics may be like when more accurate treatment of local and nonlinear effects is achieved. The theory describes the dynamics of excitatory and inhibitory synaptic action fields. EEG and MEG provide large-scale estimates of modulation of these synaptic fields around background levels. Brain states are determined by neuromodulatory control parameters. Purely local states are dominated by local feedback gains and rise and decay times of postsynaptic potentials. Dominant local frequencies vary with brain region. Other states are purely global, with moderate to high coherence over large distances. Multiple global mode frequencies arise from a combination of delays in corticocortical axons and neocortical boundary conditions. Global frequencies are identical in all cortical regions, but most states involve dynamic interactions between local networks and the global system. EEG frequencies may involve a “matching” of local resonant frequencies with one or more of the many, closely spaced global frequencies. Key Words: binding problem; cell assemblies; coherence; EEG; limit cycles; neocortical dynamics; pacemakers; phase locking; spatial scale; standing waves; synchronization. Footnotes1 The relationship between the synaptic action fields proposed in the target article and cell assemblies is clarified with Figure R1 (p. 416) of the Response. (This figure was not available to Commentators. (shrink)
Many faces of consciousness -- Ethics, religion, and the identity of self -- States of mind -- Why hearts don't love and brains don't pump -- EEG : a window on the mind -- Dynamic patterns as shadows of thought -- Networks, waves, and resonant binding -- The limits of science : What do we really know? -- Modern physics, cosmology, and consciousness -- The weird behavior of quantum systems -- Ontological interpretations of quantum mechanics -- Does the brain create (...) the mind? (shrink)
Introduction to mind and brain -- The science and philosophy of mind -- A brief look into brain structure and function -- States of mind -- Signatures of consciousness -- Rhythms of the brain -- Brain synchrony, coherence, and resonance -- Networks of the brain -- Introduction to the hard problem -- Multiscale speculations on the hard problem -- Glossary.
EEG and synaptic action fields provide experimental and theoretical entry points into brain complexity. Such entry is distinguished from the core system of cell assemblies assumed to underlie cognitive processing. The global theory of synaptic action predicts several new properties of EEG, providing limited penetration into brain complexity.
Multiscale dynamics, linear approximations, global boundary conditions, experimental verification, and global influences on local cell assemblies are considered in the context of Wright & Liley's work. W&L provide a nice introduction to these issues and a reasonable simulation of intermediate scale dynamics, but the model does not adequately simulate combined local and global processes.