Cortical high-threshold and low-activation characteristics in adolescent depression: a cross-age differential...

Adolescent depression exhibits distinct neurophysiological features, with marked age heterogeneity particularly in the resting motor threshold (RMT) measured during repetitive transcranial magnetic stimulation (rTMS), and substantial variability in clinical therapeutic efficacy. Functional near-infrared spectroscopy (fNIRS) enables the assessment of cortical excitability levels; however, research investigating the association between RMT and cortical activation in adolescent patients with depression remains limited. This study aims to elucidate the underlying neural mechanisms from the perspective of cortical hemodynamics, which is crucial for further optimizing neuromodulation strategies in patients with depression.

We collected data from 85 treatment-naive patients with depression who underwent rTMS therapy. All patients completed RMT measurement, fNIRS examination, and Hamilton Depression Rating Scale (HAMD) assessment prior to rTMS treatment. Participants were divided into three groups according to age: the adolescents group (n=31), the young adult group (n=26), and the middle-aged group (n=28). We compared the differences in RMT among the three groups and explored the relationships between RMT, cortical activation (reflected by prefrontal oxyhemoglobin level changes during the verbal fluency task via fNIRS), and depression severity (assessed by HAMD scores).

The results demonstrated that the adolescents group had a significantly higher RMT than the other age groups (58.00 ± 11.14, P < 0.001), accompanied by the lowest prefrontal Oxy-Hb activation level (0.095 ± 0.06, P < 0.001). A strong negative correlation was observed between RMT and cortical activation (Spearman's rs= -0.929, P < 0.001), while a strong positive correlation was found between RMT and depression severity (Spearman's rs = 0.837, P < 0.001). The distinct coupling phenomenon of high threshold-low activation-severe symptoms was most prominently manifested in this age group, which may theoretically reflect an underlying dysregulation in broader emotional networks, though the current direct findings strictly indicate localized alterations in prefrontal activation and motor cortical excitability.

The characteristics of high RMT and low cortical activation in adolescent depression serve as important neurobiological markers for depression severity. This finding provides a novel direction for developing individualized, developmentally tailored neuromodulation strategies (e.g., optimization of rTMS targets and dosages), indicating that interventions for adolescent depression should prioritize promoting the healthy integration of emotional circuits and the functional coordination between the cortex and subcortex.