Repeated patterns of distributed synchrony in neuronal assemblies.

Models of brain function predict that the recurrence of a process or state will be reflected in repeated patterns of correlated activity. Previous work on medullary raphe assembly dynamics revealed transient changes in impulse synchrony. This study tested the hypothesis that these variations in synchrony include distributed nonrandom patterns of association. Spike trains were recorded simultaneously in the ventrolateral medulla, n. raphe obscurus, and n. raphe magnus of four anesthetized (Dial), vagotomized, paralyzed, and artificially ventilated adult cats. The "gravitational" representation of spike trains was used to detect moments of impulse synchrony in neuronal assemblies visualized as variations in the aggregation velocities of particles corresponding to each neuron. Template matching algorithms were developed to identify excessively repeating patterns of particle condensation rates. Repeating patterns were detected in each animal. The reiterated patterns represented an emergent property not apparent in either corresponding firing rate histograms or conventional gravity representations. Overlapping subsets of neurons represented in different patterns were unmasked when the template resolution was changed. The results demonstrate repeated transient network configurations defined by the tightness and duration of synchrony in different combinations of neurons and suggest that multiple information streams are conveyed concurrently by fluctuations in the synchrony of on-going activity.