To build a representation of the auditory world, neuronal circuits in neonatal rodents exhibit plasticity, allowing sensitivity to the pattern of sensory inputs. At this time, neurons construct a receptive field, which relies on a balance of excitatory and inhibitory inputs. Here, excitation and inhibition were not found to be co-tuned upon hearing onset, but later an adjustment in the excitatory input strength occurred. Thus a fine adjustment in synaptic inputs, rather than more radical changes such as input pruning, may refine mature receptive fields.