Neurochemical brain imaging of treatment response in geriatric depression

Since the renewed emphasis on the heterogeneity of geriatric depression and the impact on treatment response variability over a decade ago,¹ neuroimaging methods have been increasingly applied to understand the underlying neurobiology of treatment response variability in geriatric depression.² The application of neuroimaging methods has resulted in fundamental observations with respect to the neural circuitry and the role of the serotonin system. The observations that some patients remain symptomatic after adequate treatment with a selective serotonin uptake inhibitor (SSRI) and that despite remission of mood symptoms, residual cognitive and other behavioral deficits persist, suggest that other neurochemical mechanisms may be involved. This review will focus on neurochemical imaging research in geriatric depression that has led to an initial understanding of the neurobiological mechanisms underlying remission of depression in late life. Future research directions to investigate the mechanisms underlying treatment resistance of mood and cognitive aspects of the illness will be discussed.