The Efficacy of HD-tDCS-Augmented Step Training in Older Adults With Mild Dementia

The clinical Choice Stepping Reaction Time (CSRT) test evaluates goal-directed volitional stepping speed and accuracy. Participants stand on a designated mat and step onto indicated target panels as quickly and accurately as possible in response to standardized verbal cues across 12 test trials. Performance is recorded as the total time (in seconds) required to successfully complete all 12 correct steps using a stopwatch. Shorter completion times indicate faster reaction and better stepping performance.

Cortical activity in the bilateral dorsolateral prefrontal cortex (DLPFC) is assessed during the choice stepping task using functional near-infrared spectroscopy (fNIRS). Performance is quantified by task-evoked changes in oxygenated hemoglobin concentration (ΔHbO) relative to baseline. Greater increases in ΔHbO reflect higher cortical activation and neural recruitment during task execution.

Balance will be measured using the Berg Balance Scale (BBS). Participants' ability to maintain an upright posture during 14 functional activities (e.g., sitting, rising from a seated position, transfer between two chairs, reaching while standing) will be rated on a scale ranging from 0 to 4, with higher scores reflecting greater balance.

The Maximum Step Length test (MSLT) assesses an individual's ability to step as far as possible in a given direction (forward, backward, or sideways) and then return to the starting position without losing balance. An average of three attempts for each direction will be recorded.

Cognitive-motor dual-tasking ability will be assessed using the single-task and dual-task of the Timed Up and Go (TUG) test. This dual-task TUG combines the standard mobility assessment with a simultaneous verbal fluency task. Under the instruction of a trained assessor, participants will be asked to rise from a standard chair, walk 3 meters, turn around, return to the chair, and sit down as quickly and safely as possible, while simultaneously naming items randomly chosen from a pool of topics (e.g., animals, fruits, or modes of transportation). The total time to complete the task will be recorded. Verbal responses will be monitored to ensure task engagement.

Executive function including attention shift and processing speed will be measured using the Trail Making Test (TMT), an education-fair alternative to the traditional Trail Making Test validated in older adults. The TMT consists of two parts: TMT-A (evaluates visuospatial scanning and perceptual tracking) and TMT-B (evaluates executive divided attention and mental set-shifting). TMT-A requires participants to connect numbers in an ascending sequence (i.e., numbers 1-25) enclosed in uniform circles. TMT-B requires participants to connect numbers in an ascending sequence while alternating between two distinct geometric shapes (circles and squares, e.g., 1-circle to 2-square to 3-circle). Shorter completion times indicated better performance.

The Iconographic Falls Efficacy Scale (Icon-FES) will be used to assess participants' fear of falling during daily activities. The Icon-FES includes 10 items, each illustrated with a pictogram to facilitate comprehension, especially for individuals with cognitive impairment.

Depressive symptoms are assessed using the Geriatric Depression Scale (GDS-15). The scale consists of 15 dichotomous (yes/no) questions evaluating affective status over the past week. Total scores range from 0 to 15, with higher scores indicating more severe depressive symptoms.

The success of participant and caregiver blinding is evaluated at the end of the intervention period using a standardized end-of-study guess questionnaire. Participants and their caregivers independently indicate whether they believe the received stimulation was "active", "sham", or if they are "unsure".

Qualitative semi-structured interviews are conducted with participant-caregiver dyads and healthcare professionals/staff to explore intervention feasibility, perceived acceptability, user experiences, and contextual barriers and facilitators to implementation. Audio-recorded transcripts are analyzed to identify key determinants of intervention adoption and translation into community settings.