Abstract
Many studies have reported long-range synchronization of neuronal activity between brain areas, in particular in the beta and gamma bands with frequencies in the range of 14–30 and 40–80 Hz, respectively. Several studies have reported synchrony with zero phase lag, which is remarkable considering the synaptic and conduction delays inherent in the connections between distant brain areas. This result has led to many speculations about the possible functional role of zero-lag synchrony, such as for neuronal communication, attention, memory, and feature binding. However, recent studies using recordings of single-unit activity and local field potentials report that neuronal synchronization may occur with non-zero phase lags. This raises the questions whether zero-lag synchrony can occur in the brain and, if so, under which conditions. We used analytical methods and computer simulations to investigate which connectivity between neuronal populations allows or prohibits zero-lag synchrony. We did so for a model where two oscillators interact via a relay oscillator. Analytical results and computer simulations were obtained for both type I Mirollo–Strogatz neurons and type II Hodgkin–Huxley neurons. We have investigated the dynamics of the model for various types of synaptic coupling and importantly considered the potential impact of Spike-Timing Dependent Plasticity (STDP) and its learning window. We confirm previous results that zero-lag synchrony can be achieved in this configuration. This is much easier to achieve with Hodgkin–Huxley neurons, which have a biphasic phase response curve, than for type I neurons. STDP facilitates zero-lag synchrony as it adjusts the synaptic strengths such that zero-lag synchrony is feasible for a much larger range of parameters than without STDP.
Highlights
Coupling between different oscillators and pacemakers can generate a large range of different behaviors and has been a topic of study in many different conditions, for example in cardiac pacemaking and chemical oscillations
In order to obtain a better understanding of the possibilities for zero-lag synchronization of distant brain areas, we have investigated the proposed network of neuronal oscillators coupled indirectly by a relay oscillator (Fischer et al, 2006; Vicente et al, 2008)
We have investigated the model with both type I Mirollo– Strogatz neurons, as well as with type II Hodgkin–Huxley neurons
Summary
Coupling between different oscillators and pacemakers can generate a large range of different behaviors and has been a topic of study in many different conditions, for example in cardiac pacemaking and chemical oscillations (see e.g., Goldbeter, 1996; Koch and Segev, 1998; Roxin et al, 2005). The first studies on this topic presented experimental evidence that the relative phase of gamma oscillations in widely separated brain areas is near zero (Frien et al, 1994; Roelfsema et al, 1997; Castelo-Branco et al, 1998; Rodriguez et al, 1999; Gross et al, 2004). This result was remarkable since synchronization requires interactions between distant brain areas, which come with considerable delays due to axonal conduction and synaptic transmission
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