BDNF and major depressive disorder: 10 A clinical study showed that serum BDNF leveland decrease in hippocampus volume was highly correlated with memory andneuropsychiatric disorders. Further analysis also reported that low BDNF level can leadto decreased hippocampus volume and be considered the cause of spatial memory deficitand depression.4 BDNF injected into a depressedmouse’s brain helped alleviate the symptoms of depression.