The Journal of Neurophysiology Vol. 88 No. 4 October 2002, pp. 1634-1654
Copyright ©2002 by the American Physiological Society

Long-Range Synchronization of  and  Oscillations and the Plasticity of Excitatory and Inhibitory Synapses: A Network Model

 ¹Department of Physiology and Pharmacology, State University of New York Health Science Center, Brooklyn, New York 11203; and  ²School of Biomedical Sciences, University of Leeds, Leeds LS2 9NL, United Kingdom

Bibbig, Andrea, Roger D. Traub, and Miles A. Whittington. Long-Range Synchronization of  and  Oscillations and the Plasticity of Excitatory and Inhibitory Synapses: A Network Model. J. Neurophysiol. 88: 1634-1654, 2002. The ability of oscillating networks to synchronize despite significant separation in space, and thus time, is of biological significance, given that human  activity can synchronize over distances of several millimeters to centimeters during perceptual and learning tasks. We use computer simulations of networks consisting of excitatory pyramidal cells (e-cells) and inhibitory interneurons (i-cells), modeling two tonically driven assemblies separated by large (8 ms) conduction delays. The results are as follows. 1) Two assemblies separated by large conduction delays can fire synchronously at  frequency (with i-cells firing at  frequency) under two timing conditions: e-cells of (say) assembly 2 are still inhibited "delay + spike generation milliseconds" after the e-cell beat of assembly 1; this means that the e-cell inhibitory postsynaptic potential (IPSP) cannot be significantly shorter than the delay (2-site effect). This implies for a given decay time constant that the interneuron  pyramidal cell conductances must be large enough. The e-cell IPSP must last longer than the i-cell IPSP, i.e., the interneuron  pyramidal cell conductance must be sufficiently large and the interneuron  interneuron conductance sufficiently small (local effect). 2) We define a "long-interval doublet" as a pair of interneuron action potentialsseparated by approximately "delay milliseconds"in which a) the first spike is induced by tonic inputs and/or excitation from nearby e-cells, while b) the second spike is induced by (delayed) excitation from distant e-cells. "Long-interval population doublets" (long-interval doublets of the i-cell population) are necessary for synchronized firing in our networks. Failure to produce them leads to almost anti-phase activity at  frequency. 3) An (almost) anti-phase oscillation is the most stable oscillation pattern of two assemblies that are separated by axonal conduction delays of approximately one-half a  period (delays from 8 to 17 ms in our simulations) and that are firing at  frequency. 4) Two assemblies separated by large conduction delays can synchronize their activity with the help of interneuron plasticity. They can also synchronize without pyramidal cell  pyramidal cell connections being present. The presence of pyramidal cell  pyramidal cell connections allows, however, for synchronization if other parameters are at inappropriate values for synchronization to occur. 5) Synchronization of two assemblies separated by large conduction delays with the help of interneuron plasticity is not simply due to slowing down of the oscillation frequency. It is reached with the help of a "synchronizing-weak-beat," which induces sudden changes in the oscillation period length of the two assemblies.