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In patients with Alzheimer disease (AD), an irregular day-night rhythm with behavioral restlessness during the night makes a strong demand on caregivers and is among the most important reasons for institutionalization. A dysfunctioning circadian timing system is supposed to underlie the disturbance or at least to contribute to it. The disturbance improves with increased environmental light, which, through the retinohypothalamic tract, activates the suprachiasmatic nucleus (SCN), the biological clock of the brain. Because recent studies have indicated both direct and indirect spinal projections to the SCN, we investigated whether excitation of spinal neurons by means of transcutaneous electrical nerve stimulation (TENS) could also improve circadian rhythm disturbances in AD patients. The actigraphically obtained rest-activity rhythm of 14 AD patients showed an improvement in its coupling to Zeitgeber after TENS treatment but not after placebo treatment.