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Figure 2. Schematic overview of the functional connectivity between the SCN and the pineal and its changes from the earliest neuropathological stages of Alzheimer’s disease onward. A decrease of vasopressin mRNA levels, indicating a functional disruption of the SCN, leads to a functional disconnectivity between the SCN and the pineal. This may cause a desynchronization of the pineal clock gene oscillation and melatonin production to environmental cues, and contributes to the circadian rhythm disturbances in AD. The dark arrow lines indicate the pathway from the SCN to the pineal, including the retina-hypothalamic tract, which sends environmental light information directly to the SCN. Changes in the SCN and the pineal shown in the scheme concern mRNA level, except for melatonin. 
= a decrease of levels. 
= daily rhythm; 
= disrupted daily rhythm.
