Transgenic amyloid precursor protein (APP)-overexpressing mouse models of AD have shown amelioration of cognitive deficits following treatment with the pan-PDE4 inhibitors rolipram [20–22], roflumilast [23, 24] and FFPM [25], and with the PDE4D subtype-selective inhibitors GEBR-7b [26] and GEBR-32a [27]. Here, PDE4D is linked to Alzheimer disease.