Supporting Episodic Memory With Transcranial Direct Current Stimulation in Healthy Controls and Dementia Patients

Study Overview
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Brief Summary
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Previous studies showed that anodal tDCS applied over the dorsolateral prefrontal cortex (DLPFC) improved episodic memory performance, indicating a possible use as an intervention for patients suffering from memory impairments. At the same time, only scant evidence (provided by functional magnetic resonance imaging (fMRI) and magnetic resonance spectroscopy (MRS)) exists regarding the underlying mechanisms, thus hindering a more targeted application. The present study aims at establishing a connection between the stimulation-induced change in episodic memory performance on the behavioural level and neurophysiological parameters. TDCS effects and the underlying mechanisms will be compared between different study conditions, receiving either real anodal tDCS or sham stimulation over the left dorsolateral prefrontal cortex during an episodic memory task.

Official Title
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Supporting Episodic Memory With Transcranial Direct Current Stimulation in Healthy Young and Elderly Participants as Well as in Individuals With Memory Impairment

Conditions
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Healthy, Mild Cognitive Impairment, Alzheimer Disease

Intervention / Treatment
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* Device: real anodal transcranial direct current stimulation (tDCS)
* Device: sham transcranial direct current stimulation (tDCS)


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Written informed consent Right-handedness Non-smokers Native German speakers or comparable level of fluency Normal or corrected-to-normal vision Exclusion Criteria: Neurological or psychiatric condition (other than diagnosed cognitive impairment) Past head injuries Magnetizable implants History of seizures Current or life-time alcohol or drug abuse Pregnancy Skin diseases

Ages Eligible for Study
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Minimum Age: 20 Years
Maximum Age: 85 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: Basic Science
Allocation: Randomized
Intervention Model: Crossover Assignment
Interventional Model Description: Participants will be randomly assigned to two possible sequences of stimulation conditions. Group 1 will receive real tDCS stimulation to the left dlPFC during encoding on the first day and sham stimulation on the second day, and group 2 will receive sham stimulation during encoding on the first day and real tDCS on the second day. The participants will be randomized with equal probability to each of the two groups, using block randomization..
Masking: Double


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Real - sham anodal tDCS<br>Session 1: 20 min of 1 mA anodal tDCS applied via 5x7 cm rubber electrodes over the DLPFC (current density: 0.028 mA/cm2). Additional ramp-up and ramp-down phase at beginning and end of stimulation lasting for 15 s. Electrodes remain attached to the participant's head for the duration of the encoding phase. Session 2: 30 s of 1 mA anodal tDCS applied via 5x7 cm rubber electrodes over the DLPFC (current density: 0.028 mA/cm2). Additional ramp-up and ramp-down phase at beginning and end of stimulation lasting for 15 s. Electrodes remain attached to the participant's head for the duration of the encoding phase. | Device: real anodal transcranial direct current stimulation (tDCS)<br>* The MR-compatible neuroConn DC-Stimulator MR (neuroCare Group, Ilmenau, Germany) will be used in the study.<br>Device: sham transcranial direct current stimulation (tDCS)<br>* The MR-compatible neuroConn DC-Stimulator MR (neuroCare Group, Ilmenau, Germany) will be used in the study.<br>|
| Experimental: Sham - real anodal tDCS<br>Session 1: 30 s of 1 mA anodal tDCS applied via 5x7 cm rubber electrodes over the DLPFC (current density: 0.028 mA/cm2). Additional ramp-up and ramp-down phase at beginning and end of stimulation lasting for 15 s. Electrodes remain attached to the participant's head for the duration of the encoding phase. Session 2: 20 min of 1 mA anodal tDCS applied via 5x7 cm rubber electrodes over the DLPFC (current density: 0.028 mA/cm2). Additional ramp-up and ramp-down phase at beginning and end of stimulation lasting for 15 s. Electrodes remain attached to the participant's head for the duration of the encoding phase. | Device: real anodal transcranial direct current stimulation (tDCS)<br>* The MR-compatible neuroConn DC-Stimulator MR (neuroCare Group, Ilmenau, Germany) will be used in the study.<br>Device: sham transcranial direct current stimulation (tDCS)<br>* The MR-compatible neuroConn DC-Stimulator MR (neuroCare Group, Ilmenau, Germany) will be used in the study.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Episodic memory performance - learning curve | Number of encoded words during the three consecutive immediate retrievals in the encoding phase | 0.25 hours | 
| Episodic memory performance - delayed recall 1 | Number of remembered words in the delayed recall after a short delay at the day of the on-site visit | 20 min after encoding phase | 
| Episodic memory performance - delayed recall 2 | Number of remembered words one day after learning | 1 day after on-site visit | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Neurotransmitter levels | Changes in neurotransmitter levels (gamma-Aminobutyric acid (GABA) and glutamatergic metabolites (Glx) due to tDCS (comparing pre- and post-stimulation measurements in DLPFC) | 0.5 hours |