Loss of dopamine D2 receptors has been reported to play both motor and cognitive roles in Alzheimer's disease [36] and L-dopa administration has been reported to produce a marked reversal of the abnormalities of motor cortical excitability such as decreased intra-cortical inhibition (ICI) in Alzheimer's disease patients [37]. The gene discussed is DRD2; the disease is early-onset autosomal dominant Alzheimer disease.