Neural Oscillations and Synchrony in Brain Dysfunction and Neuropsychiatric Disorders It’s About Time

N euraloscillationsare rhythmic fluctuationsover time intheactivity or excitability of single neurons, local neuronalpopulations or assemblies, and/or multiple neuronal as-semblies distributed across brain regions. Although trains of action potentials or spikes from single neurons can contribute to these rhythmic fluctuations, theymainly reflect inhibitory and excitatory postsynaptic currents.Neural oscillationsmanifest as cyclic changes in the voltages of local field potentials from patches of brain tissue and, via volume conduction, the voltagesmeasured on the cortical surface (electrocorticogram) or the scalp (electroencephalogram [EEG])andassociatedmagnetic fieldsmeasurednear thescalp (mag-netoencephalogram). These voltage fluctuationswouldnot be evi-dentonspatial scales ranging fromlocal fieldpotentials toscalpEEGs if theywerenot synchronized in timeand spaceacross largegroups of neurons (because electric fields that are randomly aligned, in-stead of synchronized, tend to cancel out). Synchronized oscilla-tionsmayallowspikes fromassembliesofneurons tohaveagreater effect on downstream targets than can be achieved by unsynchro-nizedneurons,1,2 andbrain regionsmaybeable to interactonlywhen oscillatingsynchronously.1,3Synchronizedneuraloscillationsaregen-erally understood to depend on inhibition that paces assemblies of pyramidal (excitatory)neurons toproducealternating temporalwin-dowsof reducedand increasedexcitability.1 This synchronization is achieved by the extensive networks of local and long-range feed-forward and feedback bidirectional connections between neurons in themammalianbrain.Moreover, the temporal frequenciesofneu-ral oscillations, includingultraslow (<1Hz), delta (1-3Hz), theta (4-