Dynamic Changes in ALFF and DC in Subthreshold Depression Before and After ICBT Intervention

Subthreshold depression (SD) is a highly prevalent mental health condition and a key precursor in major depressive disorder. Internet-based cognitive behavioral therapy (ICBT) effectively treats SD in clinical settings, but the neuromechanisms behind its success are not fully understood. This study aimed to examine changes in intrinsic brain activity in SD and their further alterations after ICBT intervention.

Twenty-five individuals with SD and 25 matched healthy controls (HC) were enrolled. SD underwent the same MRI scans and clinical assessments before and after a five-week ICBT intervention. HC underwent a single MRI scan during enrollment. The amplitude of low-frequency fluctuation (ALFF) and degree centrality (DC) are established analytical techniques in the field of neuroimaging to assess intrinsic brain activity. Two-sample and paired-sample t-tests were employed to examine changes in whole-brain ALFF and DC. Pearson or Spearman correlation analysis was performed to evaluate associations between altered ALFF/DC values and changes in clinical assessment scores in SD.

Compared with HC, decreased DC in the right precuneus (PCUN) and increased ALFF in the right insula (INS) were found in SD before ICBT intervention. After ICBT intervention, ALFF in the left hippocampus (HIP) was increased, and DC in the right medial and paracingulate gyri (DCG) was reduced in SD. Altered ALFF values in the left HIP showed a negative correlation with changes in PHQ-9 scores, and a positive correlation with changes in FATS-ReB scores. Altered DC values in the right DCG were positively correlated with changes in CCTS-TR-BhA scores.

These findings provide new insights into the altered intrinsic brain activities in SD. More importantly, this study found potential changes in intrinsic activity in brain regions associated with ICBT response to SD, which may help further explore the neuropsychological mechanism underlying the efficacy of ICBT in the future.