Cortical systems for multimodal sensory integration

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The classical view of parallel sensory processing and multimodal integration in association multimodal cortical areas has been challenged by the increasing evidence that the acquisition and initial processing of sensory information within primary sensory cortices can be influenced by another sensory modality. For instance, in human, the primary visual cortex can be activated during tactile discrimination tasks. In addition, neurons in the auditory cortex can respond to somatosensory or to visual stimuli alone in normal or in experimentally intermodal rewired animals. Evidence for cross-modal activation of the auditory cortex also comes from imaging studies in musicians and in deaf subjects. In addition to cross-modal activations of primary sensory cortices in normal subjects, such activation are clearly shown in auditory and tactile stimulation in early blind subjects. These findings are supported by recent demonstrations of direct and indirect anatomical connections between primary auditory and visual cortical areas in rodents, carnivores and in non-human primates. Although the importance of multisensory perception and integration is well-established, the underlying neural substrates have remained unclear. It has been hypothesized that multisensory integration is predominantly a 'bottom-up' process, where different modalities converge in higher order multimodal areas in the cerebral cortex. Alternatively, feedback ('top-down') projections from multimodal to unimodal areas have been stressed. Although cortical connectivity has been widely studied, fine microcircuitry and phenotypes of cortical cells engaged in particular connections are generally lacking. The main objectives of this proposal is to investigate the fine structure of cortical axons and of cells involved in multisensory integration at the cortical level. This will allow for the elaboration of model systems that are needed to explain the physiology of integrated perception.