Cover legend: Calcium imaging in a living cerebellar Purkinje cell loaded with the calcium-sensitive dye Oregon Green BAPTA-2 in a mouse cerebellar slice. This picture shows in false colors the projection of the resting level of fluorescence acquired by a confocal laser microscope on multiple planes of the cell. Variations of calcium intensity can be detected in spines in response to climbing fiber stimulation. This calcium signaling is partly mediated by NMDA receptors in adult rodents and plays a key role in synaptic gain control. For more information, see the article by Piochon et al. in this issue (pages 15330–15335).