Silicon Neurons that Inhibit to Synchronize

We present a network of silicon neurons that achieve robust synchrony using mutual inhibition. Synchrony strongly influences neuronal spike timing within many brain regions, potentially playing a crucial role in computation. Yet it has been largely ignored in neuromorphic systems, which use mixed analog and digital circuits to model neurobiology in silicon. Our neurons synchronize by using shunting inhibition (conductance-based) with a synaptic rise-time. Synaptic rise-time promotes synchrony by delaying the effect of inhibition, providing an opportune period for neurons to spike together. Shunting inhibition, through its voltage dependence, inhibits neurons that are late more strongly (delaying the spike further), pushing them into phase (in the next cycle). We fabricated a chip with 256 inhibitory neurons and 1,024 excitatory neurons in 0.25mum CMOS. We show that synchronized inhibitory neurons (population of 256) spike with a period that is proportional to the synaptic rise-time. We use these neurons to entrain the excitatory neurons, implementing a form of object binding