1. A method for selectively propagating signals through a neuromorphic circuit comprising a set of interconnected neurons implemented as an electrical circuit, the method comprising: receiving, at a neuron in the set of neurons, signal-carrying current pulses from one or more upstream signal-carrying neurons in the set of neurons, wherein the signal-carrying current pulses are insufficient to cause the neuron to generate output current pulses; and receiving, at the neuron, selectively generated gating current pulses from one or more gating neurons in the set of neurons; wherein the gating current pulses cause a neural voltage of the neuron to approach a firing threshold, whereby concurrently received signal-carrying current pulses combine with the gating current pulses to cause the neural voltage to exceed the firing threshold, which causes the neuron to generate output current pulses that propagate to downstream neurons wherein the set of neurons includes an upstream population of neurons and a downstream population of neurons; wherein neurons in the upstream population are connected to neurons in the downstream population through weighted links, wherein a firing rate of a given neuron in the downstream population is a weighted sum of inputs to the given neuron from the upstream population of neurons; and wherein a vector encoded in signal-carrying current pulses from the upstream population of neurons is transformed through a matrix operation defined by the weighted links to produce a transformed vector of signal-carrying current pulses that is propagated through the downstream population of neurons by applying gating current pulses to the downstream population of neurons.