Modulation of Memory Consolidation in Humans

Study Overview
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Brief Summary
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The goal of the present study is to optimize effects of slow oscillatory transcranial direct current stimulation (so-tDCS) on sleep physiology and memory consolidation in humans by combining computational and experimental human models in an iterative process. The investigator therefore works in cooperation with Prof. Dr. Klaus Obermayer (TU Berlin), who contributes computation models with the aim to mechanistically understand the impact of different perturbations on sleep-related electrophysiological features, and to subsequently optimize so-tDCS parameters for inducing SO and spindle activity.

Detailed Description
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Sleep plays an active role in long-term consolidation of memories. Specifically, slow oscillations (SO, large amplitude waves <1 Hz) and sleep spindles (8-15 Hz), that can be measured by electroencephalography (EEG), appear to be critical for declarative memories. According to the active system consolidation account, newly encoded memories are reactivated during sleep, accompanied by sharp-wave ripple events (80-100 Hz) in the hippocampus, and redistributed to cortical long-term storage networks through a coordinated dialog between the hippocampus and neocortex. This dialog is supposedly mediated by a particular coupling between cortical SO and thalamo-cortical fast spindles (12-15 Hz), with spindles preferably occurring during SO up-phases, and hippocampal ripples grouped at the troughs of fast spindles. Slow spindles (8-12 Hz) are a separate kind of sleep spindle activity whose function in memory consolidation is less well understood. Interventions targeting sleep parameters may not only make it possible to beneficially modulate a vital aspect of memory consolidation, i. e., sleep-dependent memory consolidation, but may also help to delineate which specific elements of the neural dynamics during sleep are crucial for successful consolidation.

Official Title
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Modulation of Memory Consolidation in Humans

Conditions
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Sleep

Intervention / Treatment
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* Other: Device: anodal tDCS
* Other: Device: no stimulation


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Adults aged between 50-80 years screened as healthy in a structured telephone interview Exclusion Criteria: Mini Mental Status Examination scores below 24 history of severe untreated medical, neurological, and psychiatric diseases sleep disorders alcohol or substance abuse brain pathologies identified on MRI scan intake of medication acting primarily on the central nervous system (e.g., antipsychotics, antidepressants, benzodiazepines, or any type of over-the-counter sleep-inducing drugs such as valerian), nonfluent German language abilities.

Ages Eligible for Study
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Minimum Age: 50 Years
Maximum Age: 80 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Other
Allocation: Randomized
Intervention Model: Crossover Assignment
Interventional Model Description: 7 experimental stimulation conditions (including sham stimulation) are tested in a randomized, counterbalanced, within-subject design
Masking: Double


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Slow oscillating transcranial direct current stimulation (so-tDCS)<br>7 experimental daytime naps with so-tDCS of different frequencies (fixed frequency of 0.75 Hz versus individually adapted frequency) and durations (5 min, 2 min, 30 sec) (Crossover assignment, applicable for each participant) | Other: Device: anodal tDCS<br>* anodal current modulated by an oscillatory component including a fixed (0,75 Hz) versus individually adapted so-tDCS frequency with three different stimulation durations (5 min, 2 min, 30 sec)<br>|
| Sham Comparator: Sham stimulation<br>sham so-tDCS during a daytime nap (Crossover assignment, applicable for each participant) | Other: Device: no stimulation<br>* sham stimulation<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Changes in EEG power (μV²) of the slow oscillation frequency band (0.5-1 Hz) following so-tDCS during sleep | Investigation whether 7 different protocols of anodal tDCS (including SHAM) lead to distinct changes in slow oscillation power | up to 20 weeks | 
| Changes in EEG power (μV²) of the sleep spindles frequency band (12-15 Hz) following so-tDCS during sleep | Investigation whether 7 different protocols of anodal tDCS (including SHAM) lead to distinct changes in sleep spindle power | up to 20 weeks | 
| Changes in cross-frequency coupling (resultant vector length) between slow oscillations and sleep spindles following so-tDCS during sleep | Investigation whether 7 different protocols of anodal tDCS (including SHAM) lead to distinct changes in coupling between slow oscillations and sleep spindles | up to 20 weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Sleep architecture | Proportion of time spent in different sleep stages (in %) during the entire nap and following so-tDCS | up to 20 weeks | 
| Changes in EEG power (μV²) of the delta frequency band (1-4 Hz) following so-tDCS during sleep | Investigation whether 7 different protocols of anodal tDCS (including SHAM) lead to distinct changes in delta power | up to 20 weeks | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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memory consolidation