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キーワード:
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要旨:
Traditionally it is assumed that information from different sensory systems merges in higher association
cortices. Contrasting this belief, we demonstrate cross-modal integration in primary and secondary auditory
cortex.
Using a combination of high-resolution functional magnetic resonance imaging (fMRI) and
electrophysiological recordings in macaque monkeys, we quantify the integration of visual and tactile
stimulation with auditory processing. Integration manifests as enhancement of activity that exceeds a simple
linear superposition of responses, i.e. auditory activity is enhanced by the simultaneous presentation of
non-auditory stimuli. Audio-somatosensory integration is reliably found at the caudal end and along the lateral
side of the secondary auditory cortex. Regions with significant integration respond to auditory but only few to
somatosensory stimulation. Yet, combining both stimuli significantly enhances responses. This enhancement
obeys the classical rules for cross-modal integration: it occurs only for temporally coincident stimuli and
follows the principle of inverse effectiveness; integration is stronger for less effective stimuli. Audio-visual
integration is similarly found along the caudal end of the temporal plane in secondary auditory cortex, but also
extends into primary auditory fields.
Complementing these results from functional imaging, enhancement of neuronal activity is found in
electrophysiological recordings of single neuron and population responses. Hence, we conclude that
cross-modal integration can occur very early in the processing hierarchy - at the earliest stage of auditory
processing in the cortex. Further, this multisensory integration occurs pre-attentive, as demonstrated in
anaesthetized animals. Such early integration might be necessary for quick and consistent interpretation of our
world and might explain multisensory illusions where a stimulus perceived by one modality is altered by a
stimulus in another modality.
