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Abstract

Our brain integrates the information provided by the different
sensory modalities into a coherent percept, and recent studies
suggest that this process is not restricted to higher association
areas. Here we evaluate the hypothesis that auditory cortical fields
are involved in cross-modal processing by probing individual
neurons for audiovisual interactions. We find that visual stimuli
modulate auditory processing both at the level of field potentials
and single-unit activity and already in primary and secondary
auditory fields. These interactions strongly depend on a stimulus’
efficacy in driving the neurons but occur independently of stimulus
category and for naturalistic as well as artificial stimuli. In addition,
interactions are sensitive to the relative timing of audiovisual
stimuli and are strongest when visual stimuli lead by 20--80 msec.
Exploring the underlying mechanisms, we find that enhancement
correlates with the resetting of slow (~10 Hz) oscillations to
a phase angle of optimal excitability. These results demonstrate
that visual stimuli can modulate the firing of neurons in auditory
cortex in a manner that depends on stimulus efficacy and timing.
These neurons thus meet the criteria for sensory integration and
provide the auditory modality with multisensory contextual information
about co-occurring environmental events.