Recruitment
Eligible patients will be recruited by Yueyang Hospital of Integrated Traditional Chinese and Western Medicine affiliated to Shanghai University of Traditional Chinese Medicine. And the hospital will post research advertisements (poster) to recruit patients. The current study protocol used the SPIRIT reporting guidelines[40].
Eligibility criteria
(1) Inclusion criteria
① First-ever stroke patients diagnosed through imaging examination (CT/MRI);
② Age ≥ 18 years old and ≤ 85 years old, regardless of gender;
③ No history of brain injury;
④ The Montreal Cognitive Assessment (MoCA) scores range from 15 to 26 points;
⑤ Primary school education or above, able to recognize and memorize common Chinese characters;
⑥ Willing to cooperate in completing experimental tasks and sign an informed consent form.
(2) Exclusion criteria
① The condition of cerebrovascular disease is progressing;
② Previous history of epilepsy or family history of epilepsy, recent use of antiepileptic drugs;
③ Wearing pacemakers, intracranial metal implants, or having skull defects;
④ Severe heart, liver, kidney diseases, etc., cannot tolerate the test;
⑤ Having mental illnesses such as depression and schizophrenia;
⑥ Difficulty in completing tests due to visual and auditory impairments, aphasia, agnosia, and apraxia.
(3)Test termination criteria
① Serious adverse reactions occur and it is not advisable to continue participating in the study;
② Sudden progression or serious complications during the trial process;
③ The subjects had poor compliance and did not receive treatment according to regulations;
④ Resolutely demand self withdrawal from research.
Study design
The prospective study is a 2-week, single blind, randomized, controlled trial. Thirty six eligible participants aged between 18 and 85 with mild PSCI will be recruited. Before the experiment begins, the doctor will provide specific information about the trial to patients both orally and in writing. All patients will voluntarily sign an informed consent provided by the attending doctor. The informed consent was approved by the ethics committee before the formal experiment begins. All patients will be screened according to eligibility criteria. This study will randomly divide 36 subjects into two groups, the TIS group and the tACS group, with 18 subjects in each group. The treatment and evaluation did not perform simultaneously. The first assessment will be completed the day before the intervention (T1). The second assessment was scheduled after the last intervention (T2).
Considering that the focus of this experiment is to explore the effects of different stimulation target depths and stimulation frequencies on PSCI, the parameters selected are as follows: TIS group: 2005Hz and 2010Hz stimulation of the hippocampus region; tACS group: 5Hz stimulation of the dorsolateral prefrontal cortex (DLPFC). The treatment cycle for each group is the same, which is a two-week intervention treatment. Stimulation is performed once a day for 25 minutes, five times a week. The overall schematic diagram and schedule for the study are respectively shown in Fig. 1 and Table 1.
Randomization and blinding
The randomized grouping design was adopted in this study to ensure the comparability of baseline characteristics between the two groups of patients, thereby reducing potential bias. Specifically, we allocated 36 patients equally to the TIS group and tACS group with 18 patients in each group through the random sequence generated by the random number table. This randomization strategy helps to balance known and unknown confounding factors and improve the internal validity of the research results. To ensure the objectivity of the assessment, an evaluator blind method was implemented in this study. In this design, the assessor was blinded to the grouping of patients. Through the implementation of blinding, we aimed to reduce the possible subjective bias in the evaluation process, thereby enhancing the reliability and accuracy of the research results. To ensure the effective implementation of blinding, we took strict measures to hide the grouping information until the data analysis was completed.
Interventions
Patients will be divided into TIS group and tACS group, all groups received conventional treatment. The tACS and TIS used in this study are 1×1 Low-Intensity Transcranial Electrical Stimulator and Interferential Neuromodulation System produced by Soterix Medical in the United States. Before the stimulation began, the subjects were fitted with EEG positioning caps. First, the electrode position was determined, and the subjects received the stimulation in the relaxed state of sitting.
TIS group: The target area of stimulation is the hippocampus. Specifically, the TIS system is able to program and send the alternating currents via four channels (four pair of electrodes). In this study, the frequency of the currents was set at 2005Hz for two channels and 2010Hz for the other two channels. The frequency difference (Δf) on each target was 5 Hz (Δf = 2010–2005 Hz). The stimulation duration was 25 minutes.
TACS group: The target areas of stimulation are the DLPFC and the parietal lobe. The parameters of tACS were similar to those used in TI, that is, sinusoidal currents with a 5Hz frequency value were used. Patients receive tACS treatment 5 times a week for 2 weeks (once a day). The duration of each tACS application is 25 minutes.
Clinical outcome assessment
We will assess clinical outcomes using the Montreal cognitive assessment (MoCA), digital span test (DST), shape trail test (STT), N-back task and fNIRS assessments. All clinical assessments and fNIRS data will be obtained at pre-intervention (T1) and post-intervention (T2). The MoCA is the primary clinical outcome of interest in this study, with the other outcomes as secondary clinical outcomes.
Primary outcome
As a valid and reliable measure, MoCA will be used as the primary outcome in this study to evaluate the cognitive ability of patients. The MoCA score is a widely used and sensitive screening tool for mild cognitive impairment, covering multiple cognitive domains such as attention, executive function, memory, language, visuospatial ability, etc. By comparing the MoCA score changes of the TIS group and the tACS group before and after the intervention, this study aims to evaluate the impact of the intervention measures on patients' cognitive function.
Secondary outcomes
The DST is used to evaluate the short-term memory and attention of patients. In the test, patients were asked to repeat a series of numbers, and the length of the numbers gradually increased to measure the maximum number sequence length that patients could accurately recall. Through digit span test, we can further understand whether the memory and attention abilities of patients are affected by the intervention measures.
The STT is a visual tracking and attention test that requires patients to connect a series of shapes in a specific order. This test is similar to the widely used trail making test, but uses shapes rather than numbers or letters. Shape continuous test is helpful to evaluate patients' visual search, attention conversion and executive function.
The N-back task is used to evaluate the working memory ability of patients. In the n-back test, patients were asked to compare whether the stimuli currently presented were the same as those before n stimuli. This study paid special attention to the 1-back task, which is to compare whether the current stimulus is the same as the previous one.
fNIRS assessments
This study will employ fNIRS to investigate the neural mechanisms underlying the effects of TIS and tACS on cognitive function in PSCI. As a non-invasive neuroimaging technique, fNIRS measures changes in hemoglobin concentration on the scalp surface, enabling the inference of brain activity. We will use it to monitor cerebral blood flow changes in patients during both resting state and while performing a 1-back task, a cognitive task that assesses working memory. Resting state fNIRS will be employed to examine the functional connectivity patterns of the brain at baseline, providing insights into the intrinsic neural networks and their potential alterations in PSCI patients. In contrast, task state fNIRS will reveal changes in brain activation patterns during the execution of the 1-back task, allowing for the assessment of the neural correlates of working memory performance. Specifically, we will analyze changes in cerebral blood flow, functional connectivity, and task-related activation patterns before and after the intervention in both the TIS and tACS groups.
Adverse events
The common adverse reactions of the transcranial electrical stimulation device used in this study are: (1) some patients have temporary tension headache during or after the evaluation process, which can be relieved after rest or taking painkillers; (2) A very small number of patients will have temporary tinnitus, which can be prevented by wearing earplugs. It is usually very mild, and no specific discomfort has been found and the patient has complained of it.
If any exception occurs, the investigator will stop the examination immediately and handle it accordingly.