BDNF and depressive symptom measurement: A recent RCT showed that CCT improves cognition and increases serum level of brain-derived neurotrophic factor (BDNF) – a neurotrophic factor important for neurogenesis and synaptic plasticity and implicated in depression and cognitive impairment (14, 15) – in non-depressed older adults (16, 17); nevertheless, evidence of CCT improving LLD via BDNF is lacking.