  Neuronal firing activities have attracted a lot of attention since a large
population of spatiotemporal patterns in the brain is the basis for adaptive
behavior and can also reveal the signs for various neurological disorders
including Alzheimer's, schizophrenia, epilepsy and others. Here, we study the
dynamics of a simple neuronal network using different sets of settings on a
neuromorphic chip. We observed three different types of collective neuronal
firing activities, which agree with the clinical data taken from the brain. We
constructed a brain phase diagram and showed that within the weak noise region,
the brain is operating in an expected noise-induced phase (N-phase) rather than
at a so-called self-organized critical boundary. The significance of this study
is twofold: first, the deviation of neuronal activities from the normal brain
could be symptomatic of diseases of the central nervous system, thus paving the
way for new diagnostics and treatments; second, the normal brain states in the
N-phase are optimal for computation and information processing. The latter may
provide a way to establish powerful new computing paradigm using collective
behavior of networks of spiking neurons.
