  There are several indications that brain is organized not on a basis of
individual unreliable neurons, but on a micro-circuital scale providing Lego
blocks employed to create complex architectures. At such an intermediate scale,
the firing activity in the microcircuits is governed by collective effects
emerging by the background noise soliciting spontaneous firing, the degree of
mutual connections between the neurons, and the topology of the connections. We
compare spontaneous firing activity of small populations of neurons adhering to
an engineered scaffold with simulations of biologically plausible CMOS
artificial neuron populations whose spontaneous activity is ignited by tailored
background noise. We provide a full set of flexible and low-power consuming
silicon blocks including neurons, excitatory and inhibitory synapses, and both
white and pink noise generators for spontaneous firing activation. We achieve a
comparable degree of correlation of the firing activity of the biological
neurons by controlling the kind and the number of connection among the silicon
neurons. The correlation between groups of neurons, organized as a ring of four
distinct populations connected by the equivalent of interneurons, is triggered
more effectively by adding multiple synapses to the connections than increasing
the number of independent point-to-point connections. The comparison between
the biological and the artificial systems suggests that a considerable number
of synapses is active also in biological populations adhering to engineered
scaffolds.
