A Study on the Efficacy of Dual-Carrier-Frequency Transcranial Alternating Current Stimulation Modulating the Hippocampus for the Treatment of Chronic Non-Specific Low Back Pain

A 100-mm visual analogue scale is used, with "0" indicating no pain and "10" indicating the worst possible pain; the subject marks the current pain level on the scale, and the distance (mm) from the left end is measured as the VAS score

A high-frequency linear array ultrasound probe (≥10 MHz) is placed over the erector spinae and multifidus muscles; cross-sectional and longitudinal gray-scale images are acquired in standardized positions, and muscle thickness, cross-sectional area, and echo intensity are measured using image analysis software to assess morphological and structural changes

Inertial measurement unit (IMU) sensors integrating tri-axial accelerometers, gyroscopes, and magnetometers are attached to the subject's lumbar region and bilateral lower limbs; continuous data on acceleration, angular velocity, and orientation are collected during standardized walking and trunk movement tasks, and gait parameters, trunk range of motion, and symmetry indices are calculated using dedicated algorithms

A 25-item self-administered questionnaire is used, with each item scored from 0 to 4 (never to always); the total score ranges from 0 to 100, with higher scores indicating a higher degree of central sensitization

A whole-head magnetoencephalography system is used to record spontaneous brain magnetic signals in a shielded room during the resting state; source localization algorithms are applied to reconstruct the magnetic signals from the scalp to the intracerebral source space, and spectral power and functional connectivity of the hippocampus and pain-related brain regions are assessed

Blood oxygen level-dependent (BOLD) functional imaging is performed using a 3.0T or higher MRI scanner; the subject remains in a resting state during scanning, and functional connectivity is assessed by measuring the temporal synchronization of low-frequency BOLD signal oscillations between brain regions, with a focus on connectivity changes between the hippocampus, prefrontal cortex, and somatosensory cortex

A multi-channel functional near-infrared spectroscopy system is used, with optodes placed over the scalp regions corresponding to the prefrontal cortex and sensorimotor cortex; changes in oxygenated and deoxygenated hemoglobin concentrations are monitored in real time by measuring near-infrared light attenuation, reflecting regional cerebral functional activity.

Surface electrodes are placed symmetrically over the bilateral erector spinae and multifidus muscle bellies; sEMG signals are recorded during standardized functional movements (e.g., trunk flexion and extension), and after amplification, filtering and root mean square (RMS) processing, time-domain and frequency-domain parameters are extracted to assess muscle activation patterns and fatigue

The 17-item version of the Hamilton Depression Scale is administered by a trained evaluator through a structured interview; the total score ranges from 0 to 52, with higher scores indicating more severe depressive symptoms.

The 14-item version of the Hamilton Anxiety Scale is administered by a trained evaluator through a structured interview; the total score ranges from 0 to 56, with higher scores indicating more severe anxiety symptoms.

A standardized self-administered questionnaire comprising sensory, affective, and evaluative dimensions is used; the subject selects the most appropriate pain descriptors based on personal pain experience, and the Pain Rating Index (PRI) and Present Pain Intensity (PPI) scores are calculated

A 10-item self-administered questionnaire (covering pain intensity, personal care, lifting, walking, sitting, standing, sleeping, sex life, social life, and traveling) is used; each item is scored 0-5, and the sum is expressed as a percentage of the maximum possible score (0-100%), with higher percentages indicating more severe disability

A 19-item self-administered questionnaire comprising 7 component scores (subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction) is used; each component is scored 0-3, and the sum yields a global PSQI score (0-21), with a score >5 indicating poor sleep quality

Scalp electroencephalography is recorded using the international 10-20 electrode placement system during both resting and task states; signals are amplified, filtered, and digitized, and power spectral density across frequency bands (δ, θ, α, β, γ) and EEG microstate features are extracted to assess changes in spontaneous neural electrical activity