It has been revealed that, from a pre-onset stage of Alzheimer's disease, enhancement of phosphorylations of MARCKS and the like causes abnormal spine formation or the like, consequently developing the disease. Moreover, it has also been revealed that the phosphorylations of MARCKS and the like are caused by PKC and the like, and further that b-raf is involved in the phosphorylation of a tau protein important for the progression of Alzheimer's disease. Thus, these proteins have been found to be target molecules useful in the diagnosis and treatment of Alzheimer's disease. In addition, it has also been revealed that, pre-onset in a stage of frontotemporal lobar degeneration also, b-RAF phosphorylation enhancement causes a decrease in the number of spines and the like, consequently developing the disease. Thus, b-RAF has been found to be a target molecule useful in the diagnosis and treatment of frontotemporal lobar degeneration.