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

Interference currents of 2 kHz and 2.010 kHz are delivered through scalp electrodes to produce a 10 Hz modulation effect in the right hippocampus. The stimulation current is gradually increased from 0.5 mA to 2 mA, and electrode placement is optimized using a head model. A total of 10 sessions are administered (5 sessions per week for 2 weeks), with routine pain rehabilitation performed immediately after each session.

Dual-carrier-frequency transcranial alternating current stimulation is based on the interference principle. Two pairs of carrier-frequency alternating currents with slightly different frequencies are applied to the scalp. After intracranial superposition, the nonlinear response of biological tissues generates a low-frequency envelope-modulated electric field in deep brain regions. This interference electric field oscillates periodically at the difference between the two carrier frequencies, enabling entrainment and modulation of neuronal rhythms in deep structures. This distinguishes it from conventional transcranial electrical stimulation, in which electric field intensity decays exponentially with depth, predominantly affecting superficial cortical layers and having limited efficacy in modulating deep nuclei.

In terms of safety, this technique is a non-invasive stimulation method. Adverse effects are limited to mild tingling or itching at the electrode contact sites, indicating favo

• Temporal interference (TI)

In addition to the parameters used in the TI group, an intermittent theta-burst stimulation (iTBS) pattern is superimposed. All other parameters, including current intensity, target region, treatment frequency, total course, and subsequent rehabilitation, are identical to those of the TI group.

Dual-carrier-frequency transcranial alternating current stimulation is based on the interference principle. Two pairs of carrier-frequency alternating currents with slightly different frequencies are applied to the scalp. After intracranial superposition, the nonlinear response of biological tissues generates a low-frequency envelope-modulated electric field in deep brain regions. This interference electric field oscillates periodically at the difference between the two carrier frequencies, enabling entrainment and modulation of neuronal rhythms in deep structures. This distinguishes it from conventional transcranial electrical stimulation, in which electric field intensity decays exponentially with depth, predominantly affecting superficial cortical layers and having limited efficacy in modulating deep nuclei.

In terms of safety, this technique is a non-invasive stimulation method. Adverse effects are limited to mild tingling or itching at the electrode contact sites, indicating favo

• Temporal interference (TI)

Cortical electrical stimulation is applied, with electrodes primarily placed over the primary somatosensory cortex (S1 region) to activate superficial cortical layers and modulate the sensorimotor network. Stimulation intensity is set within the tolerated range. Each session lasts 20 minutes, and the treatment frequency, total course, and subsequent rehabilitation are consistent with those of the previous two groups.

Cortical electrical stimulation is a neuromodulation technique in which electrodes are placed on the surface of the cerebral cortex or over the dura mater to deliver weak electrical currents for direct modulation of local neuronal electrical activity. By either exciting or inhibiting neuronal firing in specific cortical regions, it can regulate functional brain networks and is commonly used in studies on brain function mapping, neurorehabilitation, and pain modulation.

Electrode placement and the operational procedures are identical to those of the TI group. However, the current output during the treatment is 0 mA, with only the onset and offset sensations of stimulation being simulated, and no effective frequency difference or envelope modulation is generated. The treatment course, frequency, and subsequent rehabilitation are the same as those of the other groups, aiming to maintain blinding without producing any neuromodulatory effects.

Dual-carrier-frequency transcranial alternating current stimulation is based on the interference principle. Two pairs of carrier-frequency alternating currents with slightly different frequencies are applied to the scalp. After intracranial superposition, the nonlinear response of biological tissues generates a low-frequency envelope-modulated electric field in deep brain regions. This interference electric field oscillates periodically at the difference between the two carrier frequencies, enabling entrainment and modulation of neuronal rhythms in deep structures. This distinguishes it from conventional transcranial electrical stimulation, in which electric field intensity decays exponentially with depth, predominantly affecting superficial cortical layers and having limited efficacy in modulating deep nuclei.

In terms of safety, this technique is a non-invasive stimulation method. Adverse effects are limited to mild tingling or itching at the electrode contact sites, indicating favo

• Temporal interference (TI)

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