This trial aims to investigate whether a single session of 40 Hz hippocampal temporal interference stimulation can improve memory function and dual-task postural control among older adults with mild cognitive impairment (MCI). The primary research questions to be addressed are as follows:
* Can 40 Hz hippocampal temporal interference stimulation boost memory test performance in older adults with MCI? * Can 40 Hz hippocampal temporal interference stimulation improve walking and balance ability under dual-task conditions in older adults with MCI? Researchers will compare active 40 Hz hippocampal temporal interference stimulation against sham stimulation to identify whether this intervention yields positive immediate effects on memory function and dual-task postural control.
Participants will be required to:
* Attend three laboratory visits over approximately three weeks, and receive one session of active stimulation and one session of sham stimulation in random order, with an interval of at least seven days between the two stimulation visits; * Complete memory and motor function assessments before and after each stimulation session; * Undergo functional magnetic resonance imaging (fMRI) scans to detect changes in brain activity.
Aged 65 years or older;
Presence of subjective memory complaints;
Objective cognitive impairment: screened using the Montreal Cognitive Assessment-Bejingversion (MoCA-BJ). The MoCA-BJ total score is 30 points. For individuals with <12 years ofeducation, 1 point is added to the raw total score (corrected total score capped at 30 points); acorrected total score <26 points indicates risk of cognitive impairment;
Clinical Dementia Rating (CDR) score of 0.5;
None
Crossover
Temporal Interference Stimulation
DeviceTranscranial temporal interference stimulation (TIS) is a noninvasive brain stimulation technique. In this randomized crossover trial, each participant receives two sessions in random order: one active 40 Hz TIS session targeting the left hippocampus and one sham session, with at least 7 days between sessions. Each session lasts 20 minutes. Outcome measures include memory tests, dual-task postural control assessments, and fMRI scans, conducted before and immediately after each session.
Change From Pre-intervention in Object-Scene Associative Memory Retrieval Accuracy After Stimulation
Retrieval accuracy is assessed using a computerized object-scene associative memory task programmed in E-Prime 3.0. Accuracy is calculated as the number of correct match/non-match responses divided by the total number of valid retrieval trials and multiplied by 100. The reported outcome is the post-intervention value minus the pre-intervention value within each stimulation period. Higher percentages indicate better associative memory retrieval performance.
Change From Pre-intervention in Object-Scene Associative Memory Retrieval Reaction Time After Stimulation
Reaction time is recorded by E-Prime 3.0 during the retrieval phase of the computerized object-scene associative memory task. The measure is the mean reaction time across valid trials with correct responses. Trials with no response, reaction times shorter than 300 milliseconds, or reaction times more than 3 standard deviations above the participant-specific mean are excluded according to the prespecified data-cleaning procedure. The reported outcome is the post-intervention value minus the pre-intervention value within each stimulation period. Shorter reaction times indicate greater retrieval efficiency.
Change From Pre-intervention in Left Hippocampal Task-Evoked BOLD Signal During Associative Memory Retrieval
Task-state functional magnetic resonance imaging is acquired while participants perform the object-scene associative memory task. The measure is the mean blood-oxygen-level-dependent (BOLD) percent signal change within a prespecified anatomically defined left hippocampal region of interest during correct associative memory retrieval relative to the task control condition. The reported outcome is the post-intervention value minus the pre-intervention value within each stimulation period. Positive values indicate increased retrieval-related activation of the left hippocampus.
Change From Pre-intervention in Dual-Task Cost of 3-Meter Timed Up and Go Completion Time After Stimulation
Participants perform the 3-meter Timed Up and Go test under single-task and dual-task conditions. During the dual-task condition, participants complete the test while continuously subtracting 3 from a randomly selected three-digit number. Total completion time is measured in seconds using the Mobility Lab wearable motion analysis system. Each condition is tested three times, and the mean completion time is used. Dual-task cost is calculated as: \[(dual-task completion time - single-task completion time) / single-task completion time\] × 100%. The reported outcome is the post-intervention value minus the pre-intervention value within each stimulation period. A higher dual-task cost indicates greater deterioration in mobility performance under cognitive load.
Change From Pre-intervention in Dual-Task Cost of 7-Meter Walking Speed After Stimulation
Participants complete the 7-meter walking test at their usual comfortable speed under single-task and dual-task conditions. During the dual-task condition, participants walk while continuously subtracting 3 from a randomly selected three-digit number. Walking speed is measured in meters per second using the Mobility Lab wearable motion analysis system. Each condition is tested three times, and the mean walking speed is used. Dual-task cost is calculated as: \[(single-task walking speed - dual-task walking speed) / single-task walking speed\] × 100%. The reported outcome is the post-intervention value minus the pre-intervention value within each stimulation period. A higher dual-task cost indicates a greater reduction in walking speed under cognitive load.
Number of Participants With Any Stimulation-Associated Adverse Symptom
Safety is assessed using a standardized adverse-reaction questionnaire completed immediately after each stimulation session. Prespecified symptoms include tingling, itching, burning sensation, pain, skin redness, fatigue, visual sensations, difficulty concentrating, and mood changes. Each symptom is rated as none, mild, moderate, or severe, corresponding to scores of 0, 1, 2, and 3, respectively. Other spontaneously reported symptoms are also recorded. For each stimulation condition, a participant is counted as having an adverse symptom if at least one prespecified or spontaneously reported symptom is present with a severity score of 1 or higher during or immediately after stimulation.
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