Neuroscientists have generally viewed learning as being implemented by a few, generic synaptic plasticity rules, with the specialization for specific behavioral tasks arising from the circuit architecture.  In contrast, I will describe evidence that the synaptic plasticity rules themselves can be precisely tuned to functional requirements.  More specifically, my laboratory discovered heterogeneity in the learning rules implemented by different subsets of parallel fiber-to-Purkinje cell synapses in the cerebellum. Our results suggest that the rules governing synaptic plasticity at these synapses are tuned to compensate for circuit-level feedback delays, thereby solving the temporal credit assignment problem.