Mechanisms underlying declarative memory consolidation are changing with age – Insight from healthy and disturbed sleep

Abstract

Today there are little doubts about the role of sleep for memory consolidation. Yet, (i) study samples are not always well controlled for age and (ii) data appears inconsistent when it comes to patients groups. Our current studies explore whether age influences sleep-dependent declarative memory consolidation in a population of insomnia patients, as well as healthy sleeper controls. Firstly, 24 insomnia subjects were divided in two age groups: younger (25.75 ± 6.34) and older (43.92 ± 3.85). Participants learned a list of 80 word-pairs in the evening. Afterwards, they underwent two cued recall sessions, one before and one after 8 h of nocturnal sleep (with full polysomnography). In a follow-up study we extended the previous experiment (investigating two age groups with 34 controls and 25 patients) and also added an interference learning condition in the morning. Data revealed that overnight memory change [OMC] was associated with percent of N3 sleep in older patients ( r = .540, p = .070). Moreover, OMC correlated (i) in younger patients with slow sleep spindle [SS] activity during N3 ( r = .545, p = .067), but (ii) in older patients with slow NREM oscillations (density: r = .681, p < .05; slope: r = .578, p < .05). Preliminary analysis of the follow-up study on the other hand revealed that in older controls OMC was associated with REM sleep ( ρ = .478, p < .05). Lastly, resistance to interference correlated with (i) SS in older controls and (ii) older patients (slow SS in N3) and (iii) with fast N2 SS in younger patients. Our findings highlight the potential modulating effect of age for mechanisms of “offline” memory consolidation. Research was supported by the Austrian Science Foundation (FWF: P-21154-B18 and I-934). Additionally, D.P.J. Heib is associated and supported by the FWF Doctoral College “Imaging the Mind” at the University of Salzburg (FWF-W1233).