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subthreshold membrane potential oscillations
Subthreshold membrane potential oscillations are rhythmic fluctuations of the voltage difference between the interior and exterior of a neuron, in the nervous system.
Neurons produce action potentials when their membrane potential increases past a critical threshold. If the voltage is below the threshold the neuron does not fire, but the membrane potential still fluctuates due to postsynaptic potentials and intrinsic electrical properties of neurons. In some type of neurons, the membrane potential can oscillate at specific frequencies. Although subthreshold oscillations do not directly result in neuronal firing, they may facilitate synchronous activity of neighboring neurons. It may also facilitate computation, particularly processing of sensory signals
== Overview ==
Neurons display, beyond synaptic and action potentials, rhythmic subthreshold membrane potential oscillations (a particular type of neural oscillations). These oscillations, which resembled sinusoidal wave forms were originally discovered in the mammalian inferior olive nucleus cells.〔Llinas R. and Yarom Y. (1986) "Oscillatory properties of guinea-pig inferior olivary neurones and their pharmacological modulation: an in vitro study". J. Physiol 376:163-182〕 The functional relevance of subthreshold oscillations concerns the nature of the intrinsic electrical properties of neurons, that is, the electrical responsiveness not derived from interactions with other cells. These properties define the dynamic phenotype independently from form or connectivity. Subthreshold oscillation frequency can vary, from few Hz to over 40 Hz and their dynamic properties have been studied in detail in relation to neuronal activity coherence and timing in CNS, in particular with respect to the 10 Hz physiological tremor that controls motor execution, Theta rhythm in the entorhinal cortex〔Alonso, A. and Llinas, R. (1989) "Subthreshold Na+-dependent theta-like rhythmicity in entorhinal cortex layer II stellate cells". Nature, 342: 175-177. , gamma band in cortical inhibitory interneurons〕 and gamma band activity in cortical inhibitory interneurons〔Llinas R. Grace, A.A. and Yarom, Y. (1991) " In vitro neurons in mammalian cortical layer 4 exhibit intrinsic oscillatory activity in the 10 to 50 Hz frequency range". PNAS, 88, 897-901〕 and in thalamus neurons.〔Pedroarena, C. and Llinas, R. (1997) "Dendritic calcium conductances generate high frequency oscillation in thalamocortical neurons". PNAS, 94: 724-728〕 They have also been described and studied in layers V of the entorhinal cortex,〔Schmitz D.1; Gloveli T.; Behr J.; Dugladze T.and Heinemann U. (1998). “Subthreshold membrane potential oscillations in neurons of deep layers of the entorhinal cortex”. Neuroscience, 85:. 999-1004〕〔Agrawal N, Hamam BN, Magistretti J, Alonso A, Ragsdale DS. (1999).“Persistent sodium channel activity mediates subthreshold membrane potential oscillations and low-threshold spikes in rat entorhinal cortex layer V neurons.” J. Gen. Physiol 114:491-509〕〔Giocomo L. M., Zilli, E A. Fransén, E, and Hasselmo M.E. (2007).“Temporal Frequency of Subthreshold Oscillations Scales with Entorhinal Grid Cell Field Spacing” Science 315: 1719 - 1722〕 the inferior olive in vivo,〔Khosrovani, S., Van Der Giessen, R. S., De Zeeuw C. I., and De Jeu M. T. G. (2007). “In vivo mouse inferior olive neurons exhibit heterogeneous subthreshold oscillations and spiking patterns” PNAS 104 : 15911-15916〕 the olfactory bulb〔Desmaisons, D., Vincent J.D. and Lledo, P.M. (1999). “Control of action potential timing by intrinsic subthreshold oscillations in the olfactory bulb output neurons”. J, Neuroscience 19: 10727-10737〕 and the dorsal cochlear nucleus.〔Manis, P.B., Molitor, S.C. and Wu, H.(1999) “Subthreshold oscillations generated by TTX-sensitive sodium currents in dorsal cochlear nucleus pyramidal cells”. Exp. Brain Research 153: 443-451〕 The dynamic aspects of such oscillations have been defined using mathematical modeling.〔Hutcheon,B and Yarom, Y. (2000) "Resonance, oscillation and the intrinsic frequency preferences of neurons" TINS 23:216-222〕〔Izhikevich E.M., Desai, N.S, Walcott, E.C. Hoppensteadt. (2003) "Bursts as a unit of neural information: selective communication via resonance TINS" 26:161-167.〕
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