Transcutaneous Auricular Vagus Nerve Stimulation for Liver Qi Stagnation and Spleen Deficiency Type Irritable Bowel Syndrome: efficacy and Mechanism Exploration of Brain-Gut-Microbiota Axis

INTERVENTION: Experimental group:Electro‐neurostimulation therapy on the distribution area of the auricular branch of the vagus nerve;Control Group:Electro‐neurostimulation therapy in the non‐vagal nerve distribution area; CONDITION: Diarrhea‐predominant Irritable Bowel Syndrome PRIMARY OUTCOME: IBS symptom severity scale;Visual Analogue Scale;Heart Rate Variability;functional magnetic resonance imaging;Brain‐gut peptide;inflammatory biomarkers;gut microbiota; SECONDARY OUTCOME: Hamilton Anxiety Rating Scale;Hamilton Depression Rating Scale;Irritable Bowel Syndrome Quality of Life Scale;Pittsburgh Sleep Quality Inde XScale; INCLUSION CRITERIA: 1) Sign a written informed consent to participate in the trial; 2) Be male or female, at least 18 years old or older and under 70 years old on the day of signing the informed consent; 3) Be patients who meet both the Western diagnostic criteria for IBS‐D and the Chinese medicine symptom diagnostic criteria.