Slow sleep spindle and procedural memory consolidation in patients with major depressive disorder

Figures & data

Figure 1 Experimental design.

Notes: Both groups performed 12 training trials of the MST at 2.00 pm on the first day and reperformed the test 24 hours later. Brain activity during the nocturnal sleep period was recorded using digitized polysomnography (including EEG). For analysis, sets of four sequential trials were grouped and averaged, creating six averaged scores in total.
Abbreviations: EEG, electroencephalography; MST, motor sequence test.

Table 1 Summary of the participants’ demographic data and sleep variables (mean ± standard error of the mean)

	Healthy controls (n=17, 15 males)	Patients (n=11, 7 males)	P-value
Age (years)	33.76±1.38	30±2.89	ns
PSQI	5.65±0.42	11.73±1.36	<0.001
Epworth sleepiness	6.65±0.56	7.55±1.3	ns
scale
HAM-D	0.29±0.14	12.30±1.5	<0.001
Sleep efficiency (%)	90.84±1.62	78.98±4	ns
TST (minutes)	425.71±21.86	496.05±33.93	ns
SOL (minutes)	7.47±1.23	30.09±5.62	ns
REM sleep latency	100.41±11.29	183.09±24.31	0.002
(minutes)
Stage 1 (minutes)	60.32±6.07	107.23±19.8	ns
Stage 2 (minutes)	237.24±13.39	286.59±19.86	0.002
Stage 3 (minutes)	26.85±2.68	22.72±4.72	ns
Stage 4 (minutes)	34±5.16	23.5±8.66	0.049
SWS (minutes)	60.85±6.65	45.77±12.85	0.002
REM (minutes)	67.29±6.86	56.45±10.13	ns

Abbreviations: HAM-D, Hamilton Depression Rating Scale; ns, not significant; PSQI, Pittsburgh Sleep Quality Index; REM, rapid eye movement; SOL, sleep onset latency; SWS, slow-wave sleep; TST, total sleep time.

Figure 2 Performance improvement on the MST.

Notes: (A) Plot of each score. (B) Averaged scores of each four-trial group. Error bar indicates standard error of the mean.
Abbreviation: MST, motor sequence test.

Figure 3 Difference between practice-dependent learning (presleep and postsleep) and overnight improvement (overnight).

Notes: The white bar indicates the subtracted difference between the third and first groups of averaged scores, indicating presleep practice-dependent learning. The black bar indicates the subtracted difference between the fourth and third average scores, indicating overnight sleep-dependent memory consolidation. The gray bar indicates the subtracted difference between the sixth and fourth averaged scores, indicating postsleep practice-dependent learning. ^*P<0.05 (Benjamini–Hochberg’s method). Error bar indicates standard error of the mean.
Abbreviation: NS, not significant.

Figure 4 Correlations with offline memory improvement.

Notes: (A) Correlation between the extent of offline memory improvement and age. (B) Correlation between the extent of offline memory improvement and non-REM stage 2 sleep. (C) Correlation between the extent of offline memory improvement and SWS.
Abbreviations: ns, not significant; REM, rapid eye movement; SWS, slow-wave sleep.

Figure 5 Overnight improvement and slow-frequency spindle activity.

Notes: (A) Correlation between overnight improvement and the power of slow-frequency spindles during stages 2–4 of NREM sleep in the left parietal region (channel C3). (B) Topographical distribution of the correlation between the extent of overnight improvement and slow-frequency spindles obtained during stages 2–4 of NREM sleep in control participants (top panel) and patients with depression (bottom panel). Color bar indicates the Pearson correlation value.
Abbreviations: NREM, non-rapid eye movement; ns, not significant.