Dendritic spines, small actin-rich protrusions from dendritic shafts, are the primary locus of excitatory synapses on neurons. Changes in dendritic spine morphology play a key role in memory formation and learning (Kasai et al., 2003). The loss or malformation of spines is also linked to many neurological diseases, which indicates the importance of proper regulation of spine morphology (Calabrese et al., 2006). Spines come in a wide range of sizes and shapes, even within the same brain region and the same dendrite. Individual spines also change shape continuously. Developmental shape changes follow a progressive replacement of the thin, elongated, and highly motile filopodia-like structures by more stable dendritic spines, which reach morphological maturity with a distinct neck and head (Oray et al., 2006). The actin cytoskeleton is central to numerous cellular processes involving membrane dynamics such as motility, morphogenesis, and endocytosis. During these processes, the barbed ends of polymerizing actin filaments push the membrane and promote the formation of plasma membrane protrusions or invaginations (Pollard and Borisy, 2003; Kaksonen et al., 2006;