How does noninvasive brain stimulation during nocturnal slow wave ...

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slow oscillatory activity (SWA; 0.5-1Hz), spindel activity) by exogenous transcranial slow oscillating stimulation (tSOS) during NREM sleep in young healthy ...
How does noninvasive brain stimulation during nocturnal slow wave sleep affect EEG- activity and performance in a visual memory task in healthy older adults? Sven Paßmann1, Nadine Külzow1, Sascha Tamm2, Agnes Flöel1 1Department

of Neurology, NeuroCure Cluster of Excellence, Neurocure Clinical Research Center, Charite-Universitätsmedizin, Berlin 2Departement of Experimental and Neurocognitive Psychology, Center for Applied Neuroscience, Freie Universität Berlin contact: [email protected]

Introduction Previous studies demonstrated an improvement in both overnight retention of word-pairs and associated neurophysiological events (frontal

slow oscillatory activity (SWA; 0.5-1Hz), spindel activity) by exogenous transcranial slow oscillating stimulation (tSOS) during NREM sleep in young healthy subjects (1). Given the coincidence of age-related decline in memory and SWA, these results are encouraging in terms of boosting SWA and in parallel memory consolidation in the elderly. However, a recent study using the same word-pair list in a sample of healthy older adults failed to show a beneficial effect (2).

Aim This study examines whether the application of tSOS (resembling the same protocol as Marshall et al.) during nocturnal sleep impact sleep

associated neurophysiological events (SWA, slow/fast spindle band) and modulate visual-spatial memory consolidation in healthy older adults .

Material / Subjects: 21 healthy older adults (64.9 ± 1.3, 11 male) Methods

Design: • 2 nights, cross-over with counterbalanced tSOS / SHAM stimulation, separated by at least 2-3 weeks

Stimulation: • location: bifrontal • duration: 5 x 5min-blocks of oscillatory stimulation, 1min artifact- and stimulation-free intervals in between • frequency: 0.75Hz, offset: 260μA, max. current density: 0,522mA/cm2 • inter-stimulus intervals monitored online for sleep stage 2 at least

Visual Recognition Task Encoding: • 38 neutral pictures (3) of different categories e.g., objects, plants, scenes; presented in one of four quadrants (Fig. 2) Recall (immediate and delayed): • OLD/NEW recognition task: 38 old intermixed with 38 new neutral pictures centered on the screen - if a picture deemed as “OLD” – a “WHERE“ response was required

anodes

Fig 1. Schematic description of procedure

Fig 2. Encoding and recall of visual spatial task

Garten - Beet

500 ms

Wo wurde das Bild gezeigt? cathodes

2000 ms

Garten - Beet

regular nocturnal sleep

Garten - Beet

Proband: SW S-J-011-Exp1N_sp.vhdr

W REM

2000 ms

Garten - Beet

S1

Garten - Beet

1000 -1500 ms

S2 S3

2000 ms

S4

encoding & M immed. recall

adaptation night

neuropsych. assessment

Time

time

9.30-10.30 pm

3000 ms

+ 22:00

23:00

00:00

11.00 pm

01:00

12.00 am

02:00

7.30 am

03:00

delayed recall 04:00

05:00

06:00

07:00

+

1000 ms

1000 ms

7.50–8.15 am

encoding trial

tSOS/SHAM

immediate-/ delayed recall

4 minutes after start NREM2

Results Visual-Recognition Task (OLD-NEW-Decision):

• Decrease in accuracy (percent correct) after stimulation

(Condition x

Time: F(1,20) = 5.08, P = .036, Fig.3)

Location (WHERE) Task: no significant effect (P > .05) Control Tasks: • no significant differences in finger-tapping, VAS-tired, affective state (PANAS) and tiredness symptoms (all P > .086) • Tension (VAS): before, but not after sleep subjects were less relaxed under SHAM compared to STIM (Condition X Time: F(1,20) = 5.08,

Sleep Stages (entire night): • no significant stimulation effects in WASO and in sleep stages, except sleep stage 4 (SP4STIM < SP4SHAM, P = .046) • no significant impact on sleep quality or sleep efficiency EEG: • inter-stimulus intervals I1-I5: significant effects only in higher frequency bins (see Fig. 4 and Table 1; non-linear Mixed Model Analyses) • SWA (0.5-1Hz) n.s. (P > .05)

P = .036)

difference from learning

4

Memory Performance

frequency band slow spindles (8-12Hz)

stim sham

*

2

0

fast spindles (12-15Hz) -2

-4

PRcorrect stim

PRcorrect sham

Fig 3. Performance measured in % correct. Results shows difference scores (morning– evening). Positive values indicate improvement.

Fig 4. stim-sham difference of mean value of power (µV), averaged over inter-stimulus interval 1-5 for slow (8-12Hz) and fast (12-15Hz) spindle band

electrode site prefrontal

b .132*

SE b .061

95% CI .01, .25

frontal

.112†

.060

-.01, .23

central

.153**

.057

.04, .27

centroparietal

.139*

.062

.02, .26

parietal

.085

.061

-.04, .21

prefrontal

.176**

.059

.06, .29

frontal

.123*

.058

.01, .24

central

.132*

.057

-.03, .29

centroparietal

.097

.062

-.03, .22

parietal

.011

.055

-.10, .12

Table 1. prefrontal (FP1, AFZ, FP2); frontal (FC1, FZ, FC2); central (C3, CZ, C4); centro-parietal (CP1,CZ,CP2); parietal (P3,PZ,P4); b = regression coefficient; SE = standard error; 95% CI = confidence interval ; † p < .10, * p < .05, ** p < .01;

Discussion • Although tDCS lead to enhanced power in spindle bands, SWA remained unaffected and in parallel visual memory performance was

impaired • discrepancy may result from differences in stimulation protocol (suggest an adapted protocol for elderly e.g., later start of stimulation) or specificity of the age group (e.g., higher intervariability on stimulation-response, age-related changes in the sleep-consolidation relationship (4))

References

1Marshall

et al. (2006). The Journal of Neuroscience 24(44): 9985–92; 2Eggert et al. (2013). Brain Stimul. 2013 Nov;6(6):938-45, 3The Multimodal Stimulus Set (MULTIMOST) was developed by Schneider TR, Debener S & Engel AK at the Dept. of Neurophysiology and Pathophysiology, University Medical Center Hamburg- Eppendorf, Germany; 4Scullin and Bliwise (2015). Perspectives on Psychological Science Vol10(1) 97–137.