Characterising resting motor threshold in depressed individuals across life span: a large retrospective study

Repetitive transcranial magnetic stimulation (rTMS) is a safe and non-invasive treatment strategy for depression. Resting motor threshold (RMT) directly determines rTMS stimulation intensity and measures general neuronal membrane excitability in the corticomotor pathway. However, RMT has yet to be characterised across age cohorts in depressed individuals, by taking into account of critical demographic information such as gender and interhemispheric asymmetry. In a large sample of depressed individuals (n = 258), this retrospective study sort to address this issue. Our results showed that older adults (≥ 50 years, n = 61) had higher RMT than depressed prime-age adults (26–49 years, n = 83). Depressed adolescents (< 18 years, n = 63) also demonstrated higher RMT than prime-age adults, but with a most prominent effect in females. In addition, interhemispheric asymmetry in RMT was observed in young female depressed adults (18–25 years, n = 51), with a higher RMT in the left versus right hemisphere. Meanwhile, no clear gender effect was observed on RMT. Overall, this study provided the first portrait of RMT development in depressed individuals across age cohorts in the context of gender and interhemispheric asymmetry. Our results may have implications for designing rTMS treatment strategies given the role of age and interhemispheric asymmetry. Older adults had higher RMT than depressed prime-age adults. Depressed adolescents also demonstrated higher RMT than prime-age adults. Young female depressed adults had lower excitability in left versus right hemisphere. No clear gender effect was observed on RMT.