Relationship of evoked EPSCs in pairs of C4- and C8-projecting corticospinal neurons from skilled forelimb grasp trained (n = 21; N = 17) vs. untrained rats (n = 25; N = 15). Analysis across all neuronal pairs indicates that skilled motor learning is associated with a significant increase in excitatory synaptic drive from layer 2/3 inputs onto the layer 5b, C8-projecting population (blue line). In contrast, evoked EPSCs in untrained rats were slightly greater in the C4-projecting population (thick gray line; thin gray line is unity line).
