ORIENTING BEHAVIOR AND SUPERIOR COLLICULUS SENSORY REPRESENTATIONS IN MICE WITH THE VIBRISSAE BENT INTO THE CONTRALATERAL HEMISPACE

When a tactile stimulus touches the body on one side, animals show an orienting response toward that side with the eyes, the head or the entire body. This movement requires the transformation of sensory information into motor commands. The superior colliculus is supposed to be a fundamental part of the brain where this sensorimotor transformation occurs and where one of the possible mechanisms could be the alignment among sensory and motor topographies. We changed the body shape of mice in order to analyse the development of new orienting responses following tactile stimulation. To do this, we bent the left vibrissae from left to right such that they were located in the right portion of the visual hemifield. If left-right inversion was performed in adults, tactile stimulation of the left vibrissae performed from the right produced wrong orienting movements to the left. Conversely, if left-right inversion was performed in newborns, mice learned to respond correctly to the right. By recording from superior colliculus multisensory neurons of mice whose vibrissae were displaced at birth, we found a shift of visual and auditory receptive fields from left to right in those multisensory neurons receiving tactile input from the displaced vibrissae. These results show the strict relation existing between the neuronal modifications in the superior colliculus and the changes in orienting behaviour. These findings also suggest two important conclusions. First, sensory mapping in the superior colliculus depends on sensory inputs coming from the same portion of space. Second, since the neuronal modifications we found involved sensory representations, the observed motor learning seems to be due, at least in part, to sensory changes, and the superior colliculus appears therefore to be an important brain region where the internal schema of the body is specified.