Background: Subjective cognitive decline (SCD) is considered to be the early risk stage of dementia. Untreated SCD comorbid with sleep disturbances may accelerate the progression of neurodegeneration (β-amyloid and tau) and lead to cognitive deficits. At present, non-pharmacological interventions for managing SCD and sleep disturbances are very limited. High-definition slow-oscillatory transcranial direct current stimulation (so-tDCS) is a newly developed frequency-specific modality of brain stimulation for promoting brain health and cognition. Notably, neurophysiological feature (impedance) during tDCS was found to be related to treatment outcomes and adverse effects (skin injury). Objectives: We propose to 1) develop a high-performing neurophysiological signal detector for tDCS and test its feasibility and flexibility in a randomized clinical trial; 2) investigate the short-term and long-term effects of high-definition so-tDCS on SCD, sleep quality and plasma Aβ and p-tau levels; 3) examine the values of neurophysiological signals in predicting the treatment outcomes at individual level. Design: A randomized, double-blind, sham-controlled trial. Methods: Chinese right-handed older adults with SCD and sleep disturbances will be randomly assigned to a 4-week intervention of either high-definition 0.75 Hz so-tDCS or sham tDCS, with 40 participants per arm. Pre-treatment magnetic resonance imaging (MRI) scans will be collected to exclude the cases with major neurological disease and quantify individual's brain features. Galvanic skin response, subjective cognitive complaints, sleep quality, plasma p-tau and β-amyloid levels and domain-specific cognition will be assessed at baseline, 4th week, 8th week and 12th week. Program adherence and adverse effects will be monitored throughout the whole intervention.
Chinese, right-handed, aged from 60 to 85 years.
Normal global cognition defined as a total score of the Montreal Cognitive Assessment Hong Kong version (HK MoCA) > 26.
Subjective cognitive decline (SCD) is evaluated by a 10-item questionnaire that covers subjective cognitive complaints (SCC) in the core cognitive domains.
Sleep disturbances or poor sleep quality is assessed and defined with a total score of the Pittsburgh Sleep Quality Index (PSQI) greater than 5.
Previous diagnosis of age-related neurodegenerative diseases, such as Alzheimer's disease, Parkinson disease.
History of neurological diseases including brain tumor, and stroke.
History of psychiatric disorders including schizophrenia and depression.
Presence of positive neurological diseases, such as stroke, brain tumor, dementia.
Parallel
so-tDCS
DeviceThe so-tDCS is delivered by a battery driven direct current stimulator (DC-Stimulator Plus, NeuroConn, Ilmenau, Germany). The high-definition setting is applied by placing an anodal electrode over the center of the treatment target and placing four cathodal electrodes surrounded the anodal electrod. Each electrode in the "4 × 1" montages had a diameter of 1.2 cm. We place the anodal electrode over the center of left dorsolateral prefrontal cortex (DLPFC) (i.e., F3 according to the international 10-20 EEG system).
Sham so-tDCS
DeviceSham so-tDCS: With a same setting of high-definition as active so-tDCS, the stimulation of sham so-tDCS only lasts for 30 seconds. The electrodes will be left in place for a further 20 minutes.
Impedance
A neurophysiological signal recorded and measured by a built-in wearable Galvanic Skin Response (GSR) sensor. The GSR sensor is placed on the fingers to detect the impedance of the skin when the participant is receiving the so-tDCS intervention
Subjective cognitive complaints (SCC)
SCC is a 10-item questionnaire that covers subjective complaints in the core cognitive domains. Participants will answer ten yes/no questions relating to the presence of cognitive complaints in the last six months. The answers of SCC are codified as 0 (no complaints) or 1 (presence of complaints). Answers will be summed up and the total of complaints will be obtained ranging from 0 to 10.
Pittsburg Sleep Quality Index (PSQI)
The PSQI is a 19-item questionnaire that includes seven areas of subjective sleep quality and patterns in adults over the last month including the following components: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, SDs, use of sleeping medications, and daytime dysfunction. Each item in the scale is scored from 0 to 3 scale (0 = no difficulty; 3 = severe difficulty). The scores are added to yield a global score ranging from 0 to 21 (0 = no difficulty; 21 = severe difficulties in all areas). This scale has good reliability and validity psychometrics and is widely used in research: Cronbach's alpha (0.77 to 0.83), sensitivity (89.6%), specificity (86.5%). Greater score of PSQI indicates worse sleep quality.
Intra-individual variability of reaction time (IIV-RT)
IIV-RT, representing the within-person fluctuations, is calculated based on the performance of attention network test (ANT). For correcting the increased RT in elderly, Intraindividual coefficient of variation of reaction time (ICV-RT) is used for assessing the IIV-RT enumerated with the formula: ICV-RT = (Standard deviation of RT/mean RT) × 100.
Objective sleep quality
Actigraphy records will be used to quantify sleep-wake cycle during treatment.
The levels of saliva Aβ
The levels of saliva Aβ , are assessed at the baseline and post-intervention time points.
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