Synchronization between populations of neurons

In order to execute cognitive functions the brain must bind features and information which
occurs at different cortical areas. The most accepted hypothesis to underlie such integration
of information is the binding by synchrony. Accordingly to it: two brain regions
interact with each other whenever they have coherent activity. The mechanism of this
phenomenon has been subject of controversial debate for many years: how can two distant
dynamical elements synchronize at zero lag even in the presence of non-negligible
delays in the transfer of information between them? So far, complex mechanisms and
neural architectures have been proposed to answer this question. However, a simple and
robust mechanism has been proposed recently. Zero-lag synchronization between two
elements is achieved by relaying the dynamics via a third mediating element. The synchronization
thus obtained is robust over a considerable parameter range. In this work we
study the dynamical relay phenomenon in complex networks of chemically coupled neurons,
specifically the capacity to provide the basis for the binding by synchrony process.
We show that three identical neuronal populations satisfy the minimum conditions to produce
lag-free synchrony among delayed populations reciprocally connected to a central
relay population. We also investigate the dynamical behavior of the thalamocortical circuit
whose relay station role is played by the thalamus. We found that the thalamocortical
circuit supports the dynamical relay mechanism. More importantly, we report the identification
of a variable that might be responsible to control the on-off synchronization of the
cortical populations depending only on the ratio of dorsal over ventral thalamus external
activity. The simplicity of the key controlling element in the model also suggests that
both bottom-up and top-down incoming stimulus to thalamic region share responsibilities
in the cortical synchronization phenomenon, in contrast to previous hypothesis. This
work supports the binding by synchrony theory and helps to establish solid bases for this
phenomenon.