# Development of input connections in neural cultures - Condensed Matter > Disordered Systems and Neural Networks

Abstract: We introduce a novel approach for the quantitative assessment of theconnectivity in neuronal cultures, based on the statistical mechanics ofpercolation on a graph. This allows us to follow the development of the cultureand see the emergence of connectivity in the network. The culture becomes fullyconnected at a time equivalent to full term. The spontaneous bursting activitythat characterizes cultures develops in parallel with the connectivity. Theaverage number of inputs per neuron can be quantitatively determined in unitsof $m 0$, the number of activated inputs needed to excite the neuron. For$m 0\sim 10$ we find that hippocampal neurons have on average $\sim 40-80$inputs while cortical neurons have $\sim 50-100$, depending on neuronaldensity. The ratio of excitatory to inhibitory neurons is determined using theGABA$\text{A}$ antagonist bicuculine. This ratio changes during developmentand reaches the final value at day $7-8$, coinciding with the expected time ofthe GABA switch. For hippocampal cultures the inhibitory cells comprise about$30\%$ of the neurons in the culture while for cortical cultures they are about$20\%$. Such detailed global information on the connectivity of networks inneuronal cultures is at present inaccessible by any electrophysiological orother technique.

Author: Jordi Soriano, Maria Rodrriguez Martinez, Tsvi Tlusty, Elisha Moses

Source: https://arxiv.org/