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Abstract

Results from functional imaging and electrophysiology suggest that responses in auditory cortex can be modulated by stimulation of other sensory
modalities. In fact, auditory responses of neurons
in primary and secondary fields are enhanced
or reduced by the simultaneous presentation of
visual or touch stimuli. Although often denoted
as sensory integration, the exact function of
these multisensory influences is unclear, and it remains to be shown whether they actually make
the auditory neurons more reliable or informative
about the acoustic environment. To scrutinize the
neuronal basis of these multisensory influences,
we investigate mechanisms of neural information
coding in the auditory cortex of the macaque.
For just acoustic stimulation, we find that temporal
neural codes, such as precise spike timing,
or the relative firing of neurons to background
activity (phase of slow field potentials) provide
considerably more information than firing rates. In
addition, these different codes can encode complementary
information about the same stimulus
epochs. Overall, this suggests that the auditory
cortex might rely on the use of several neural
codes operating on different spatial temporal
scales at the same time.
In the context of multisensory stimuli, we find
that neurons become more informative about
the stimulus when an auditory stimulus is complemented
with the matching movie. Especially
the information in firing rates benefits from the
visual stimulation, while spike times show a rather
small information gain. In addition we find that
this information gain by multisensory stimulation
is not uniformly distributed across all stimuli, but
is highest for those stimuli which elicit strong
responses.
Overall our findings suggest that visual influences
in auditory cortex might be more than just
a simple response modulation, but make neuronal
firing more reliable, and hence enhance the
information encoded in auditory cortex about the
environment.