Experience-dependent remodeling of synaptic structure and function underlies information storage in the mammalian central nervous system. Although accumulating evidence suggests synergistic roles of long-term depression (LTD) and long-term potentiation (LTP) in cerebellar motor learning, their structural correlates and operational mechanisms have not been clearly addressed. A recent three-dimensional electron microscopic study provides insight for a potential complementary interplay between LTP and LTD in local dendritic segments of Purkinje cells of motor skill-trained animals. Complex motor skill training induced strengthening of a subset of parallel fiber synapses onto Purkinje cells by forming multiple-synapse boutons (MSBs) contacting spine pairs arising from the same dendrite, whereas MSB-neighboring synapses were weakened by reducing the size of the post-synaptic density. Here, we discuss these orchestrated structural modifications of neighboring synapses that may sharpen synaptic weight contrast in local dendritic segments, leading to enhanced signal-to-noise ratio for optimal motor skill retention.
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