Regionalisation of the callosal contribution to the barrel field activity in the mouse

Synchrony of neural activity among cortical areas arises from functional coupling between those areas. Such a strong synchrony characterises the two mouse barrel fields (BFs) when the animal is deeply anaesthetised or asleep. In these conditions, neurons in the two hemispheres depolarise (up-state) and hyperpolarise to their resting potential (down-state) in a remarkably coordinated fashion. Callosal glutamatergic axons provide a means to functionally couple supra- and infragranular neurons of the two BFs. However, little is known about their relationship with the BF grid-like architecture: Are they able to influence the activity of barrel and/or septal neurons? Are there specific barrels more sensitive to the contralateral activity? To respond to these questions, we localised and counted the BF cells positive to c-Fos (c-Fos + ) resulting from a contralateral whiskers deprivation when mice were free to explore a novel environment. In layer 4, we found a greater number of c-Fos + cells in septa compared to barrels, which mainly localised in the posterior and lateral aspects of the sensory-deprived BF. To learn more about such interhemispheric recruitment, we studied the propagation of slow-oscillatory activity in anaesthetised mice. We performed whole-cell patch-clamp in the ipsilateral BF while recording LFPs in the contralateral BF. In the BF lateral region, neurons showed faster oscillatory cycles, shorter up-state duration and faster down-to-up transitions compared to neurons recorded in BF regions with a sparser c-Fos signal, suggesting the reception of extra inputs in the former. We thus propose that the lateral BF is a critical sub-region for BFs activity-coupling.