Generally speaking, most people think of what is referred to as the cerebral cortex when they think of the brain. Twisty, slightly mushy, and intricate, it’s become a source of mystery and exciting discoveries for neuroscience. One group of researchers, however, tends to ignore this area. Instead, they focus on the small, folded structure at the back of the brain. The cerebral cortex goes in the biohazard bin. The preserved structure is the cerebellum, which is often associated with motor function and motor learning. Researchers who focus on the cerebellum have the benefit of working with a generally small, well-characterized microcircuit: parallel fibers contact several the massive, complex, and beautiful dendritic arbours of Purkinje cells, while climbing fibers pick one Purkinje cell to climb, winding their way through the dendritic arbour and exploring all the branches. Purkinje cells summarize the inputs they get from these two fibers, and pass along their summary to the neurons of the deep cerebellar nuclei (DCN). DCN cells then send impulses out of the brain. Sounds simple, right? As Jenna Hotton discovered while preparing a paper reviewing the circuit of the DCN, the synaptic plasticity of this circuit can be complex.