We present a first-draft digital reconstruction of the microcircuitry of somatosensory cortex of juvenile rat. The reconstruction uses cellular and synaptic organizing principles to algorithmically reconstruct detailed anatomy and physiology from sparse experi- mental data. An objective anatomical method defines a neocortical volume of 0.29 ± 0.01 mm3 containing$31,000 neurons, and patch-clamp studies identify 55 layer-specific morphological and 207 morpho- electrical neuron subtypes. When digitally recon- structed neurons are positioned in the volume and synapse formation is restricted to biological bouton densities and numbers of synapses per connection,
their overlapping arbors form $8 million connections with $37 million synapses. Simulations reproduce an array of in vitro and in vivo experiments without parameter tuning. Additionally, we find a spectrum of network states with a sharp transition from synchro- nous to asynchronous activity, modulated by physio- logical mechanisms. The spectrum of network states, dynamically reconfigured around this transition, sup- ports diverse information processing strategies.