Three-dimensional reconstruction of the mouse vibrissal array: anatomical foundations of tactovisual integration

To form a coherent perception of the world, our brains assemble a variety of sensory inputs from different modalities. Growing evidence suggests that this multimodal processing begins in the primary sensory cortices. To investigate the spatial alignment of the tactile and visual receptive fields in the context of primary sensory cortex tactovisual integration, a novel 3D-model of the mouse vibrissal array was created. Stereophotogrammetric scans were combined with the exact whisker shapes, as traced under a microscope. Reconstruction of whisker arrays from five dead mice showed little interindividual variation in their architecture. The tactile field showed substantial overlap with the visual field represented in the primary visual cortex. Additionally, the active movement of the whisker array was simulated: While the tactile field extended beyond the borders of visual perception during retraction, protraction moved whiskers through the visual field towards its lower nasal border. Previous studies have shown that the stimulation of whiskers can suppress visually evoked activity in the primary visual cortex. This modulation is carried via a direct cortico-cortical connection from the primary somatosensory cortex. The prominently modulated region of the visual field, identified through anterograde viral tracing data and cortical retinotopy, closely aligned with the tips of protracted whiskers in the lower nasal visual field. In this region, proximate sensory cues on the ground in front of the animal are thus captured by both modalities. Analysis of potential modeling errors supported this observation. Additionally, preexisting retrograde viral tracing data implicated the long, far-reaching whiskers as key contributors to tactovisual suppression. This thesis demonstrates that tactile cues modulating visual cortical activity originate from a shared, multisensory space in proximity to the mouse head, supporting the spatial rule of multimodal processing.