The article discusses research being done on the role of the spine neck in regulating the movement of neurons into and out of the spine head. It references a study by B. L. Bloodgood and B. L. Sabatini published in a 2005 issue of "Science." The level of signaling molecules in the spine head is important for the induction of synaptic plasticity. Pairing synaptic stimulation with back-propagating action potentials also affects the rate of diffusion across the spine neck.