Interdependence of primary and secondary somatosensory cortices for plasticity and texture discrimination learning

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Feedforward and feedback pathways are important for transfer and integration of information between sensory cortical areas. Here we find that two closely connected cortical areas, the primary (S1) and secondary somatosensory cortices (S2) are both required for mice to learn a whisker-dependent texture discrimination. Increased inhibition in either area (using excitatory DREADDs expressed in inhibitory interneurones) prevents learning. We find that learning the discrimination produces structural plasticity of dendritic spines on layer 2/3 pyramidal neurones in vibrissae S1 that is restricted to the basal dendrites and leaves dendritic spines on apical dendrites unchanged. As S2 projects to the apical dendrites of S1 neurones, we tested whether S2 affects LTP-induction in S1. We found that feedback projections from S2 to S1 gates LTP on feedforward pathways within S1. These studies therefore demonstrate the interdependence of S1 and S2 for learning and plasticity in S1. HIGHLIGHTS Both primary (S1) and secondary (S2) somatosensory cortices are necessary for whisker based texture discrimination learning S2 feedback connections to S1 gate LTP at feedforward pathways in S1 S1 undergoes structural plasticity of pre-existing spines during learning S1 learning induced plasticity and LTP occurs on basal but not apical dendrites