  When a neuron breaks silence, it can emit action potentials in a number of
patterns. Some responses are so sudden and intense that electrophysiologists
felt the need to single them out, labeling action potentials emitted at a
particularly high frequency with a metonym -- bursts. Is there more to bursts
than a figure of speech? After all, sudden bouts of high-frequency firing are
expected to occur whenever inputs surge. The burst coding hypothesis advances
that the neural code has three syllables: silences, spikes and bursts. We
review evidence supporting this ternary code in terms of devoted mechanisms for
burst generation, synaptic transmission and synaptic plasticity. We also review
the learning and attention theories for which such a triad is beneficial.
