Investigating the Neural Correlates in Memory Retrieval After HD-tDCS

Study Overview
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Brief Summary
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The overall objective of this study is to investigate the neural correlate in retrieval memory task. The aim of the study is to understand the undergoing changes in late positive ERP component during retrieval memory task when stimulating the posterior cingulate cortex (PCC) with High Definition Transcranial Direct Current Stimulation (HD-tDCS).

Detailed Description
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Retrieval memory is supported by distinct retrieval process known as recollection and familiarity. These two process have been associated with distinct event related potentials (ERPs). At the time of retrieval, familiarity is associated with modulation of the FN400, an enhanced positivity for old items relative to new items observed from approximately 400-600ms post stimulus onset. The FN400 tends to have mid-frontal scalp distribution which can extend to left and right frontal areas and central midline regions. In contrast, recollection has been linked with modulation of positive going waveform that emerges approximately 600ms post stimulus and is typically maximal over parietal sites and referred to as late positive component (LPC). In addition, FN400 is found to increase gradually as a function of item retrieval confidence whereas LPC is limited to high confidence retrieval response. High Definition transcranial Direct Current Stimulation (HD-tDCS ) is a non-invasive neuromodulation technique. Compared to the standard bipolar montage used by the conventional tDCS, it uses arrays of smaller, specially designed electrodes to deliver a constant and low current directly to the cortical brain areas to increase the spatial focality. Studies show that the cortical area undergoing stimulation with HD-tDCS is more restricted compared to the standard bipolar montage of conventional tDCS. Moreover, tDCS has been proposed as a therapeutic procedure in various diseases and tDCS in healthy adults have demonstrated to improve cognitive and memory performance, but information regarding the effects of HD-tDCS targeting the PCC and its impact on memory retrieval is scarce. By targeting the PCC area by HD-tDCS, we want to introduce a safer, easier-to-use and more accurate non-invasive neuromodulation procedure. The dysfunctions of posterior cingulate cortex hav been linked to a range of psychiatric and neurological condition such as Alzheimer's disease, schizophrenia, autism, depression and attention deficit hyperactivity disorder, as well as aging. It shows increased activity when subject retrieve autobiographical memories suggests its internal orientated function. PET and ERP combined studies have shown greater blood flow medial temporal lobe with a brief late positive ERP component in PCC. Therefore, in this study we aim to understand whether HD-tDCS targeting the PCC can modulate the late positive ERP component.

Official Title
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Investigating the Neural Correlates in Memory Retrieval After HD-tDCS

Conditions
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Healthy Adults

Intervention / Treatment
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* Device: active anodal HD-tDCS
* Device: sham HD-tDCS
* Device: active cathodal HD-tDCS


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Native English Speaker Currently not using any medication Capable of understanding and signing an informed consent Exclusion Criteria: Severe disease Mental illness Cardiac history History of severe head injuries History of epileptic seizures Any implanted devices such as pacemaker, neurostimulator Pregnancy

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 35 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: Parallel Assignment
Interventional Model Description: Participants will be randomly assigned to one of three groups: (1) active HD-tDCS with retrieval memory task, (2) sham HD-tDCS with retrieval memory task, (3) active cathodal HD-tDCS with retrieval memory task
Masking: Double


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: active anodal HD-tDCS<br>Active anodal HD-tDCS stimulation applied during memory task | Device: active anodal HD-tDCS<br>* 1) active anodal HD-tDCS with memory task<br>|
| Sham Comparator: sham HD-tDCS<br>Sham HD-tDCS stimulation during memory task for comparison | Device: sham HD-tDCS<br>* 2) sham HD-tDCS with memory task<br>|
| Experimental: active cathodal HD-tDCS<br>Active cathodal HD-tDCS stimulation applied during memory task | Device: active cathodal HD-tDCS<br>* 3) active cathodal HD-tDCS with memory task<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Recognition Memory Assessed by a Retrieval Memory Experiment | Participants had to learn an association between a face and a name. The face-name association memory task was divided into (1) an encoding phase, (2) a consolidation phase, and (3) a retrieval phase. During the encoding phase, participants studied 60 successively presented face-name pairs. Participants were instructed to assess the gender of each face shown to keep participants focused on the task. The encoding phase lasted approximately 5 minutes. This is followed by a consolidation phase where participants were instructed to sit still, relax, and think about nothing in particular for 10 minutes. During the retrieval phase, participants were presented with 60 old and 60 new faces and were instructed to assess whether they had seen this face during the encoding phase, or if it was a 'new' face. Participants received active or sham transcranial direct current stimulation targetting the posterior cingulate cortex during retrieval. The outcome is correctly recalled old faces. | Retrieval Memory is assessed after 90 seconds break following the recognition phase. |