  In nature, animals encounter high dimensional sensory stimuli that have
complex statistical and dynamical structure. Attempts to study the neural
coding of these natural signals face challenges both in the selection of the
signal ensemble and in the analysis of the resulting neural responses. For
zebra finches, naturalistic stimuli can be defined as sounds that they
encounter in a colony of conspecific birds. We assembled an ensemble of these
sounds by recording groups of 10-40 zebra finches, and then analyzed the
response of single neurons in the songbird central auditory area (field L) to
continuous playback of long segments from this ensemble.
  Following methods developed in the fly visual system, we measured the
information that spike trains provide about the acoustic stimulus without any
assumptions about which features of the stimulus are relevant. Preliminary
results indicate that large amounts of information are carried by spike timing,
with roughly half of the information accessible only at time resolutions better
than 10 ms; additional information is still being revealed as time resolution
is improved to 2 ms. Information can be decomposed into that carried by the
locking of individual spikes to the stimulus (or modulations of spike rate) vs.
that carried by timing in spike patterns. Initial results show that in field L,
temporal patterns give at least ~20% extra information. Thus, single central
auditory neurons can provide an informative representation of naturalistic
sounds, in which spike timing may play a significant role.
