Matsuzaki M, Honkura N, Ellis-Davies GC, Kasai H (2004) Structural basis of long-term potentiation in single dendritic spines. Nature 429:761-766.
I've been re-reading this classic paper this week. Nice reassuringly fuzzy pictures of spines growing and shrinking, nice useful detail on how they measured spine heads, nice technique stimulating individual spines with 2-photon microscope and glutamate uncaging, nice findings with some spines growing very quickly (minutes) then fading back but still bigger than they started. Then the paper steps up another level when they perforated-patch the cell and use the post-synaptic response to the uncaging to map the size of the glatamate-sensitive area (ie the synapse presumably) on the spine, and find that this enlarges in step with the spine enlargement. Other headlines: LTP can be induced at an individual spine; neighbouring spines show no change; large spines resist LTP.