Frontotemporal degeneration patients, therefore, show a fundamentally different type of circadian abnormality than do AD patients. The expression of an entrained circadian rhythm, as an organized pattern of rest-activity, is compromised in FTD, even while a normal rhythm of core-body temperature is maintained, while, in AD, both central pacemaker and behavioral expression are altered. Therefore, in AD, treatments that act at the level of the central pacemaker, such as light or melatonin, may be effective in treating the behavioral disturbances. Dementia patients have been noted to have abnormalities in their rhythms of melatonin secretion.47,48 This dysfunction has been noted not only in patients with clinical diagnosis of AD,9 but confirmed after postmortem analysis.49 Light therapy, given after the temperature nadir, may also be an appropriate treatment. However, determining the precise temperature nadir before beginning any chronobiological treatment is important since it can occur very late in some subjects, sometimes later than 11 AM. If light were given before or during the time of the temperature nadir, the phase could be shifted in the direction opposite from expectation. Chronobiological treatments, aimed at the SCN and the endogenous circadian rhythm in FTD, are unlikely to be effective in treating the disrupted rest-activity rhythms of this form of dementia. In FTD, the central pacemaker seems to be functioning normally, with difficulties emerging downstream from the SCN. Further work is needed to understand the nature of the rest-activity rhythm disturbance in FTD.