Matthias Cavelius defense thesis - Latéralisation du traitement des informations olfactives chez la souris

Abstract

Lateralization is defined as a different use of the two brain hemispheres while performing a cognitive task. Initially described in humans by Paul Broca and Marc Dax, lateralization has been observed in many other animal species, from vertebrate to non-vertebrate species. First observed in language formation and comprehension, lateralization has been considered as an adaptative trend allowing better processing of cognitive tasks. The concept of lateralization has now been extended to many other cognitive functions and to sensory processing in somatosensory perception, audition or even vision. Nonetheless, the role of lateralization in olfactory processing retained much less interest. In this view, we studied olfactory processing and its eventual lateralization in mice. We first questioned the role of the type of the cognitive task on its possible lateralization using different olfactory learning tasks. Then, we studied the role of post-natal olfactory environment on lateralization establishment in male and female mice. Finally, we looked for lateralization depending on the hedonic value of odors. To achieve this, we measured brain activity in response to an olfactory stimulation, using the expression of the early gene cfos, a marker of neuronal activity. We compared the activity between the two hemispheres in twenty-seven brain regions of interest and used graph theory to analyze the functional connectivity of the recruited circuits. The results revealed different functional connectivity depending on the information borne by the odorant, with a higher connectivity in the left hemisphere for mice performing associative olfactory tasks. In addition, post-natal olfactory enrichment led to an impressive increase in global functional connectivity in both male and female mice. Finally, our results suggest different olfactory

processing for pleasant and unpleasant odorants. While unpleasant odorants recruit a large number of regions, pleasant odorants seem to recruit a precise network with regions of particular importance, mainly in the right hemisphere. Altogether, our data revealed lateralization of olfactory processing according to the behavioral value of the odorant and brought evidence for large effect of early-life olfactory enrichment on adult connectivity and lateralization of the odor-evoked adult brain network.