Table 7.

Comparison of previous studies using acoustic stimulation to boost slow oscillations and spindle and their effects on memory

StudyStudy designBehavioral resultsEEG results
Ngo et al., 2013N = 11 healthy young adults (mean ± SD age, 24.2 ± 2.98 years)Stimulation protocolHedges gav = 1.07
Retention (presleep − postsleep):
Stim: 22.2 ± 2.3 words
Sham: 13.0 ± 2.5 words
Increase in slow-wave and spindle power
Closed-loop
Two-pulse stimulation
overnight sleep (7 h)
Memory tests
120 semantically related word pairs
Cox et al., 2014bN = 12 healthy adults (age range, 18–23 years; 11 females)Stimulation protocolNo behavioral effect observedIncreased slow-wave amplitude and spindle band power with sounds targeted at up-state
Closed-loop
One-pulse stimulation
Evening nap (2 h)
Memory tests
Sound stimulus memory task
Ong et al., 2016N = 16 healthy young adults (mean ± SD age, 22 ± 1.4 years)Stimulation protocolHedges gav = 0.41Retention (presleep − postsleep):Sham: −1.72 ± 4.16 SDsStim: 0.0 ± 3.76 SDsIncreased slow-wave amplitude, theta, and fast-spindle activity
Closed-loopFive consecutive pulsesAfternoon nap (1.5 h)
Memory tests
40 semantically related word pairs
Weigenand et al., 2016N = 26 healthy young adults (mean age, 22.2 years; age range, 18– 28 years)Stimulation protocolNo behavioral effect observedIncrease in slow-wave and increase in spindle power with first pulse
Open-loopThree consecutive pulse stimulationOvernight sleep (7 h)
Memory tests
120 semantically related word pairs1
Leminen et al., 2017N = 15 healthy adults (mean age, 30.5 years; range, 23–42 years)Stimulation protocolHedges gav = 0.65Retention (presleep – postsleep):Stim: 21.1 ± 7.7 SDsSham: 15.6 ± 8.1 SDsNo behavioral effect on face–name memory, finger tapping, or picture memory (tasks 2–4)Increase in slow-wave and spindle power
Closed-loopSingle-pulse stimulationOvernight sleep (7 h)
Memory tests
120 semantically related word pairs2 Face–name association testFinger-tapping testPicture recognition task
Papalambros et al., 2017N = 13 healthy older adults (mean age, 75.2 years; age range, 60–84 years)Stimulation protocolHedges gav = 0.77Retention (presleep – postsleep):Stim: 9.2 ± 7.93 SDsSham: 3.1 ± 6.85 SDsIncrease in slow-wave and spindle power
Closed-loopFive-pulse, phase-locked loop stimulationOvernight sleep (8 h)
Memory tests
88 semantically related word pairs
Ngo et al., 2019N = 24 healthy young adults (mean ± SD age, 23.9 ± 3.42 years)Stimulation protocolNo behavioral effect observedAcute increase in slow-wave and spindle power, but no effect on total overnight slow-wave and spindle power
Closed-loopSeven-click spindle stimulationOvernight sleep (7 h)
Memory tests
120 semantically related word pairs1
  • For each study, the brief description of the subject pool, stimulation and memory protocols, effect size (Hedges gav) of the behavioral effect (if applicable), and overall electrophysiological findings are provided.

  • 1 Same word lists used in Ngo et al., 2013.

  • 2 Translated from list used in Ngo et al., 2013.