Structural characterization of the neural circuit responsible for control of cardiovascular functions in higher...

A comparison of structural properties of a biological neural system responsible for cardiovascular function control in higher vertebrates with randomly connected networks was pursued using matrix representations of those circuits. The biological circuit was characterized by the presence of some heavily connected nuclei in contrast to the random networks that had equally distributed connections between their elements. This property of the analysed biological circuit was shown to account for a high logarithmic correlation found between two indexes defined to represent pointwise features of the nuclei and their global contribution to the whole network. The first index is obtained by the product of the number of inputs and of outputs of a nucleus and was called power index (PI). The second one, called occurrence index (OI), defines how many times a specific nucleus is crossed when all possible pathways joining two nuclei of the circuit are obtained. This PI-OI correlation was clearly dependent on the pathway length distribution (expressed in number of synapses), and was maximal considering pathways with a low number of synapses. When randomly connected circuits were analysed lower correlation was found between the same two indexes and only for much longer pathways. Therefore, it is proposed that the analysis of the PI-OI correlation can be useful to quantify structural differences between biological neural circuits as distinguished from randomly connected networks and also between neural systems at different levels of phylogenetic and ontogenetic development.