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||p.16126 left column 4th paragraph:"Electron microscopy is required since axons and spine necks can be 50 nm or less in diameter and the structures of interest are densely packed (primary source)." See Smith 2007 PMID 18082394 p.605 left column bottom line:"It also seems certain that the resolution of electron microscopy will be necessary to measure many important details of circuit structure accurately (e.g. dendritic spine necks can be less than 50 nm wide, and spine signaling depends very strongly on spine width)."