Simultaneous intrinsic signal imaging of auditory and visual cortex reveals profound effects of acute hearing loss on visual processing.

It has been suggested that primary sensory cortices do not work in isolation but receive subthreshold inputs originating from other senses. However, repercussions of an acute loss of one sense on multimodal sensory processing remain elusive. Here we investigated the early effects of acute hearing loss on visual processing in adult mice. For this, we developed a method to simultaneously map the primary auditory (A1) and visual cortex (V1) using periodic intrinsic optical imaging. We found that reducing sound evoked A1 responsiveness due to the induction of conductive hearing loss (CHL) led to a concomitant increase of visually driven V1 activity. Accordingly, using the neuronal activity marker c-fos we found the number of stained pyramidal cells to be increased in V1 layer 2/3 after CHL. In contrast, numbers of c-fos positive parvalbumin (PV) and somatostatin (SOM) expressing inhibitory neurons were reduced after CHL. Finally, we adapted the periodic intrinsic imaging method to determine V1 contrast and spatial frequency tuning. Using this method we could show that visual acuity and contrast sensitivity were improved after CHL. In addition, retrograde tracing experiments revealed direct anatomical projections from A1 to V1 which could potentially serve as a substrate for the observed effects. In summary, our results suggest that CHL rapidly disrupts the functional interplay between A1 and V1 leading to altered visually evoked V1 responses.