This scoping review explores shared neural and neurotransmitter mechanisms in dementia and depression, conditions that frequently co-occur but remain biologically complex. Drawing on 45 studies published since 2019, it identifies key areas of overlap across brain circuits, neurotransmitter systems, and biological processes.

Strong convergence was found in hippocampal, prefrontal-cingulate, fronto-limbic, default mode, salience, and reward networks, alongside multiple neurotransmitter systems. Shared mechanisms include stress dysregulation, neuroinflammation, vascular burden, and neurodegeneration.

The review presents a comparative network model highlighting shared vulnerability while distinguishing disease-specific features. It also emphasises the importance of timing, with midlife depression as a risk factor and late-life depression as a potential prodrome. These findings may support earlier identification of dementia risk and guide future research.

 

Keywords: dementia, Alzheimer’s disease, depression, late-life depression, cognitive decline, neural circuits, neurotransmitters, hippocampus, prefrontal cortex, anterior cingulate cortex, fronto-limbic circuitry, default mode network, salience network, reward circuitry, serotonin, dopamine, acetylcholine, noradrenaline, glutamate, GABA, neuroinflammation, vascular burden, HPA axis, neuroplasticity, sleep disruption, shared vulnerability, scoping review, comparative network model.