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Alex Meredith, Brian Allman; Unimodal' visual cortical neurons are influenced by auditory inputs. Journal of Vision 2007;7(9):873. doi: 10.1167/7.9.873.
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© ARVO (1962-2015); The Authors (2016-present)
Visual neurons with multisensory responses have been identified in many cortical areas. These bimodal (or trimodal) neurons are excited by inputs from different sensory modalities and often integrate their responses to multisensory stimuli. However, the behavior of non-bimodal (e.g., ‘unimodal’) neurons in the presence of multisensory stimulation has largely been overlooked. The present experiments used extracellular recording techniques to systematically examine the activity of all neurons encountered within the posterolateral lateral suprasylvian (PLLS) visual area of the cat in response to visual, auditory and combined visual/auditory cues. A total of 360 neurons were examined, of which 49 bimodal neurons responded both to visual and to auditory stimulation, and integrated those inputs when combined. In contrast, 196 visually-responsive neurons showed no response when presented an auditory stimulus alone. However, 37 of these same apparently ‘unimodal’ neurons had their responses to visual stimulation significantly facilitated (P[[lt]]0.05, paired t-test) when visual and auditory stimuli were combined. Furthermore, while the overwhelming number (n=159) of visual neurons was not significantly influenced by auditory stimulation, they were, as a population, significantly more active in response to the combined stimuli than to the visual stimulus alone. In fact, when the multisensory response generated by all the neurons was calculated, the overwhelming proportion (69%) of the multisensory signal was carried by the neurons that would otherwise have been considered ‘unimodal.’ These data show that ‘unimodal’ visual cortical neurons can be significantly influenced by auditory stimuli at the neuronal as well as the population level, and that the behavior of bimodal neurons cannot adequately represent the multisensory processing capacity of the visual cortex.
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