Hebbian and homeostatic plasticity mechanisms are segregated in sub-types of layer 5 neuron in the visual cortex

Cortical layer 5 contains two major types of projection neuron known as IB (intrinsic bursting) cells that project sub-cortically and RS (regular spiking) cells that project between cortical areas. We studied the plasticity properties of RS and IB cells in the visual cortex during the critical period for ocular dominance plasticity in mice. RS neurons exhibited synaptic depression in response to both dark exposure (DE) and monocular deprivation (MD), and their homeostatic recovery from depression was dependent on TNFalpha. In contrast, IB cells demonstrated opposite responses to DE and MD, potentiating to DE and depressing to MD. Potentiation in IB cells depended on CaMKII- autophosphorylation and not TNFalpha. IB cells showed mature synaptic properties at the start of the critical period while RS cells matured during the critical period. Together with observations in somatosensory cortex, these results suggest that differences in RS and IB plasticity mechanisms are a general cortical property. ### Competing Interest Statement The authors have declared no competing interest.