BDNF and sleep disorder: Disturbance of neurotransmitter and hormone signal transduction (such as serotonin, norepinephrine, and melatonin) and neurotrophin BDNF may lead to disease process.[26] Sleep disorders are often observed in AD and PD patients, not only as accompanying symptoms, but also as precursor symptoms before the onset of these diseases.[27] According to the cluster analysis results, studies related to “suprachiasmatic nucleus” have attracted wide attention.