A mutant with bilateral whisker to barrel inputs unveils somatosensory mapping rules in the cerebral cortex

In mammals,tactile information is mapped topographically onto the contralatereal side of the brain in the primary somatosensory cortex (S1). In this study, We describe Robo3 mouse mutants in which a sizeable fraction of the trigemino-thalamic inputs project ipsilaterally rather than whisker maps in the thalamus and cortex. Surprisingly, these maps are segregated resulting in duplication of whisker representations and doubling of the number of barrels without changes in the size of S1. Sensory deprivation competitive interactions between the ipsi/contralateral whisker maps. This study reveals that the somatosensory system can form a somatotopic map to integrate bilateral sensory inputs, but organizes the maps different way from that in the visual or auditory systems. Therefore, while molecular pre-patterning constraints their orientation and position, preservation of the continuity of inputs defines the layout of the somatosensory maps.