Several brain behavioral, cognitive, or perceptual states are associated with temporally accurate neuronalfiring. Understanding the source of this accuracy, which occurs despite significant noise, remain afundamental problem in brain research. It has been shown that temporal accuracy can be achieved throughsynchronous synaptic neuronal drive. We note that synchronous neuronal activity also generatesextracellular field potentials and that through 'field effect interactions' and these extracellular potentials willcoherently polarize a neuronal population. This project proposes and will test two novel mechanisms bywhich the effect of small electric fields are dramatically amplified at the single neuron level and again at thenetwork level: 1) A small polarization of somatic membrane potential can significantly affect spike timing; 2)A coherent change in spike timing for a large number of neurons can profoundly affect network dynamicsand synchronization. We hypothesize that in the hippocampus, endogenous extracellular potentialscoherently polarize a neuronal population thereby increasing the accuracy of network spike timing. Thisproject aims to quantify the relationship between naturally occurring 'endogenous' extracellular fields andspike time coherence in neuronal networks. Specifically, small non-uniform fields will be applied tohippocampal slices to quantify the effect of extracellular fields on neuronal membrane potential and spiketiming of pyramidal neurons. These results will be integrated into a recurrent network model of spikingneurons to demonstrate the role of field effects in modulating coherent spiking focusing specifically ongamma and theta oscillations. This approach tightly links experimentation with modeling by combining theinvestigators expertise in electrophysiology and field effects (Bikson), and signal processing/neuronalnetwork modeling (Parra). Our results on small field amplification are equally valid for environmental electricfields (e.g. power lines) and electric fields induced by neuro-prosthetic brain stimulators (e.g. DBS) and thusrepresent a novel framework for consideration of the effects of low amplitude electric fields.PH: Our brains are exposed to electric fields generated both by the brain itself and by the environment. Thisproject will demonstrate how the brain can 'amplify1 these fields such that electric fields previouslyconsidered too small may this be relevant for normal brain function and for disease.
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