Abstract
Synchronization among neurons is thought to arise from the interplay between excitation and inhibition; however, the connectivity rules that contribute to synchronization are still unknown. We studied these issues in hippocampal CA1 microcircuits using paired patch clamp recordings and real time computing. By virtually connecting a model interneuron with two pyramidal cells (PCs), we were able to test the importance of connectivity in synchronizing pyramidal cell activity. Our results show that a circuit with a nonreciprocal connection between pyramidal cells and no feedback from PCs to the virtual interneuron produced the greatest level of synchronization and mutual information between PC spiking activity. Moreover, we investigated the role of intrinsic membrane properties contributing to synchronization where the application of a specific ion channel blocker, ZD7288 dramatically impaired PC synchronization. Additionally, background synaptic activity, in particular arising from NMDA receptors, has a large impact on the synchrony observed in the aforementioned circuit. Our results give new insights to the basic connection paradigms of microcircuits that lead to coordination and the formation of assemblies.
Highlights
Spike synchronization is crucial for motor and sensory functions; excessive coordination of neuronal firing is associated to pathological conditions (Paluszkiewicz et al, 2011)
We found that a circuit constituted by a nonreciprocal excitatory connection between pyramidal cells (PCs) that in turn received inhibitory synapses from a virtual interneuron, showed the greatest synchronization
To assure that PC cells within the pair were drawn from a single population, we only used neurons with membrane properties differing less than 10% from each other
Summary
Spike synchronization is crucial for motor and sensory functions; excessive coordination of neuronal firing is associated to pathological conditions (Paluszkiewicz et al, 2011). Two given cells or group of cells A and B can synchronize their firing if A and B are reciprocally connected or if a pacemaker cell, or group of cells, connects to both A and B (Hansel et al, 1995; Tort et al, 2007). Of note, both effects seem to take part in the generation of rhythmic patterns in the hippocampus; for example, while gamma oscillations are likely to arise form intrinsic network properties (Wang and Buzsáki, 1996), theta oscillations would depend both on intrinsic connectivity and pacemaker inputs from the medial septum (Colom, 2006)
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