Coherent periodic activity in excitatory neural networks: the role of network connectivity

Neural collective oscillations have been observed in very many context in brain circuits, ranging from ubiquitous ?-oscillations to ?-rythm in the hyppocampus. The origin of these oscillations is commonly associated to the balance between excitation and inhibition in the network, while purely excitatory circuits are believed to lead to "unstructured population bursts" [1]. However, coherent activity patterns have been observed also in "in vivo" measurements of the developing rodent neocortex and hyppocampus for a short period after birth, despite the fact that at this early stage the nature of the involved synapses is essentially excitatory [2]. Of particular interest are the so-called giant depolarizing potentials (GDPs), recurrent oscillations which repetitevely synchronizes a relatively small assembly of neurons and whose degree of synchrony is orchestrate by hub neurons [3]. Furthermore, in their recent study Bonifazi et al. [3] found that the functional connectivity of developing hippocampal networks is characterized by a power-law distribution of the output links with an exponent ? ~ 1.1 - 1.3. ......