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Synchronous activities in neuronal ensembles are ubiquitous phenomena observed in many regions of the brain using multi-electrode recording techniques [1-5]. What is the role of synchrony in information processing? I did a mathematical neuronal network modeling study, showing that appropriate background noisy activities and synaptic coupling can help generate synchronized oscillations by coherent resonance mechanism [6-8]. There exists a range of optimal synchronous states, where the information transmission rate and coding efficiency to the input signals are maximized [9-10]. It is not the weaker or stronger but an appropriate synchronous state that may be of significance in sensory encoding [9-10].

Synchrony might be miscellaneous in information coding process [1-5]. It was suggested that the precise spike timings relative to the synchronized oscillation may provide an additional temporal channel for encoding information [1,2,11]. Recent experimental studies demonstrated that firing rate and spiking timing of the neurons in hippocampus are dissociable and may encode two independent variables [12]. Learning-related synchronized oscillations also play a key role in synaptic plasticity, which was found to transform an asymmetric rate code into a temporal code [13]. Such a temporal coding scheme might be widely implemented in sensory and cortex neurons. In hippocampal cultures, most of the spontaneous spikes are triggered by synchronously arriving excitatory synaptic input, suggesting a privileged role of synchronized activity in synaptic information transmission [14]. Future works are expected to clarify the relations among network structure, synchrony and scheme of information presentation [15-17].

[1] Engel AK, Fries P and Singer W. Dynamic predictions: Oscillations and synchrony in top-down processing. Nat Rev Neurosci2,704-716 (2001).

[2]. Salinas E and Sejnowski TJ. Correlated neuronal activity and the flow of neural information.Nature Rev. Neurosci2, 539-550 (2001).

[3]. Traub RD, Jefferys JGR and Whittington MA. Fast Oscillations in Cortical Circuits. MIT Press, Cambridge, MA. (1999).

[4]. Fries P, Schroder JH, Roelfsema PR, Singer W and Engel AK. Oscillatory neuronal synchronization in primary visual cortex as a correlate of stimulus selection. J.Neurosci22 3739-3754 (2002).

[5]. Romo R, Hernandez A, Zainos A andSalinas E.Correlated neuronal discharges that increase coding efficiency during perceptual discrimination. Neuron38 649-657 (2003).

[6]. Yu, Y. and Wang, W.
Generation of Spontaneous Synchronized Rhythm and its Role in Information Processing.
Chinese Physics Letters, 18, 295-298 (2001).

[7]. Yu YG, Wang W, Wang JF and Liu F. Resonance-enhanced signal detection and transduction in the Hodgkin-Huxley neuronal systems. Phys. Rev. E63 021907 (2001).

[8] Yu, Y., Liu, F., Wang, J. and Wang, W.
Synchronized Rhythmic Oscillation in a Noisy Neural Network.
Journal of the Physical Society of Japan. 72, 3291-3296 (2003).

[9] Yuguo Yu, Feng Liu, and Wei Wang
Spike timing precision for a neuronal array with periodic signal.
Physics Letters A, 282, 23-30 (2001).

[10] Yu, Y., Liu, F., Wang W. and Lee, T.S.
Optimal synchrony state for maximal information transmission.
NeuroReport, in press, (2004).

[11]. Tiesinga PHE, Fellous JM, Jose JV andSejnowski TJ. Information transfer in entrained cortical neurons. Network: Comp Neural Syst13, 41-66 (2002).

[12]. Huxter J, Burgess N and O'Keefe J. Independent rate and temporal coding in hippocampal pyramidal cells. Nature425 828-832 (2003).

[13]. Mehta MR, Lee AK and Wilson MA. Role of experience and oscillations in transforming a rate code into a temporal code. Nature417 741-746 (2002).

[14]. Stevens CF and Zador A. Input synchrony and the irregular firing of cortical neurons.Nature Neurosci3 210-217 (1998).

[15]. Diesmann M, Gewaltig MO and Aertsen A. Stable propagation of synchronous spiking in cortical neural networks. Nature402 529-533 (1999).

[16]. Shadlen M and Movshon JA. Synchrony unbound: A critical evaluation of the temporal binding hypothesis. Neuron24 67-77 (1999).

[17]. Crook SM, Ermentrout GB and Bower JM. Spike frequency adaptation affects the synchronization properties of networks of cortical oscillators.Neural Comp10 837-854 (1998).

[18]. Strong SP, Koberle R van Steveninck RDR andBialek W. Entropy and information in neural spike trains.Phys. Rev. Lett80 197-200 (1998).

Generation and function role of synchrony

Yuguo Yu