A Cortico-Collicular Model for Multisensory Integration

Abstract

Remarkable visual-auditory cross-modal phenomena occur at perceptual level: a visual stimulus enhances or biases auditory localization in case of spatially coincident or spatially disparate stimuli. Hemianopic patients (with one blind hemifield resulting from damage to primary visual cortex) retain visual enhancement but not visual bias of auditory localization in the blind hemifield. Here, we propose a neural network model to investigate which cortical and subcortical regions may be involved in these phenomena in intact and damaged conditions. The model includes an auditory cortical area, the primary and extrastriate visual cortices and the Superior Colliculus (a subcortical structure). Model simulations suggest that: i) Visual enhancement of auditory localization engages two circuits (one involving the primary visual cortex and one involving the Superior Colliculus) that act in a redundant manner. In absence of primary visual cortex (hemianopia), enhancement still occurs thanks to the Superior Colliculus strongly activated by the spatially coincident stimuli. ii) Visual bias of auditory localization is due to an additive contribution of the two circuits. In hemianopia, the effect disappears as the Superior Colliculus is not sufficiently activated by the spatially disparate stimuli. The model helps interpreting perceptual visual-auditory phenomena and their retention or absence in brain damage conditions.