Chronic silencing of corticothalamic layer 6 pyramidal cells affects cortical excitability and tactile behavior

Cortical projections originating in layer 6 (L6) in mouse primary somatosensory cortex have an important function controlling both cortical and sub-cortical activity. To study cortical plasticity and communication between somatosensory and motor cortex, L6-Ntsr1 cells were chronically silenced using tetanus toxin and the effect this had on cortical activity and behavior was investigated. A 2 Hz stimulation protocol was used to potentiate whisker evoked local field potentials (LFP) in a layer-dependent manner in both cortices. Silencing L6 pyramidal cells, the LFP potentiation in both cortices was affected without a change in the spontaneous multi-unit activity. Animals with L6 chronically silenced used more low-amplitude whisks, which presumably compensates for a reduction in cortical excitability. These results suggest that L6 is not only an important cortical output layer that modulates sub-cortical circuits, but also that it controls cortical dynamics.