Multiplexing of visual-auditory signals in a predominantly auditory brain region.

A recent theory of neural representation postulates that neurons may fluctuate between encoding multiple items. Such competition for representation is plausible when the stimuli evoke activity in overlapping neural populations. What about when one stimulus does not? Here, we ask whether a stimulus that is poorly represented can also evoke fluctuating activity when combined with a more dominant stimulus. Specifically, we investigated responses to visual and auditory stimuli in the inferior colliculus (IC), a predominantly auditory structure. We found fluctuating activity evoked by visual-auditory stimulus combinations, indicating that fluctuations can arise even when one item is not from a brain area's preferred modality. The IC also appeared to maintain representations of multiple sounds, regardless of whether one was paired with a visual stimulus or which one was localized first. These results indicate that multimodal stimuli can evoke fluctuating activity in unimodal structures, preserving sensory information rather than filtering for attention.