Summary diagram and table of the effects of chronic cocaine on proximal dendritic spine morphometrics. In the NAc core, chronic cocaine decreases proximal dendritic spine head diameter at 4 h and by 24 h causes a selective elimination of thin spines that is maintained for up to 1 month. Conversely, in the NAc shell, which at baseline has fewer proximal thin spines than the core, new thin spines are formed by 4 h and maintained for up to 24 h. There is also an increase in proximal dendritic diameter in the shell. However, unlike the core, the changes that occur in the shell are transient because they are not observed after prolonged withdrawal from cocaine. Red arrows indicate shrinkage or elimination, and green arrows indicate growth or sprouting. * Data adapted from Kourrich and Thomas (2009).