  Studies of motor control have almost universally examined firing rates to
investigate how the brain shapes behavior. In principle, however, neurons could
encode information through the precise temporal patterning of their spike
trains as well as (or instead of) through their firing rates. Although the
importance of spike timing has been demonstrated in sensory systems, it is
largely unknown whether timing differences in motor areas could affect
behavior. We tested the hypothesis that significant information about
trial-by-trial variations in behavior is represented by spike timing in the
songbird vocal motor system. We found that premotor neurons convey information
via spike timing far more often than via spike rate and that the amount of
information conveyed at the millisecond timescale greatly exceeds the
information available from spike counts. These results demonstrate that
information can be represented by spike timing in motor circuits and suggest
that timing variations evoke differences in behavior.
