Synergistic effects of age and depression on sleep-dependent memory consolidation

Sleep is critically involved in the consolidation of motor memory: It has been shown that post-training improvements in several motor tasks strictly require a night of sleep. Considering own preliminary data, we hypothesized that this kind of memory consolidation is strongly impaired in depressed older patients compared to depressed younger patients and healthy controls. 12 young (22–30 years) and 23 older (32–64 years) medicated patients with an acute episode of major depression (MD) and 35 healthy matched controls were assessed using a sequential motor learning task: On the first day (between 0900 and 1200h), subjects were required to repeatedly tap a sequence of 5 numbers during 12 periods of 30s, interrupted by a 20s pause each, as often and correctly as possible on a computer keyboard. Changes of motor performance were measured in a three periods test session 24h later, after a night of sleep. In the older-age group healthy subjects showed a better overall performance than patients and a 18% overnight increase in the number of correctly tapped sequences, whereas patients showed a 12% overnight decrease (p<.01). In the young-age group, however, patients and controls showed almost the same motor performance and overnight increase (24% vs. 25%). There were no differences in training improvement between any of the groups. Our results clearly show that age and an acute episode of MD exert strong synergistic effects on sleep-dependent motor memory consolidation.