Thalamocortical inputs show post-critical-period plasticity

Experience-dependent plasticity in the adult brain has clinical potential for functional rehabilitation following central and peripheral nerve injuries. Here, plasticity induced by unilateral infraorbital (IO) nerve resection in 4-week-old rats was mapped using MRI and synaptic mechanisms were elucidated by slice electrophysiology. Functional MRI demonstrates a cortical potentiation compared to thalamus 2 weeks after IO nerve resection. Tracing thalamocortical (TC) projections with manganese-enhanced MRI revealed circuit changes in the spared layer 4 (L4) barrel cortex. Brain slice electrophysiology revealed TC input strengthening onto L4 stellate cells due to an increase in postsynaptic strength and the number of functional synapses. This work shows that the TC input is a site for robust plasticity after the end of the previously defined critical period for this input. Thus, TC inputs may represent a major site for adult plasticity in contrast to the consensus that adult plasticity mainly occurs at cortico-cortical connections.