Objective:

To synthesize clinical and preclinical evidence delineating the mechanistic pathway of Light Therapy (LT) from the reception of peripheral light signals to the remodeling of central brain functions.

Approach:

• Clinical Efficacy: Summarizes the clinical efficacy of LT, including its parameter dependence and application in various forms of depression.
• Neural Pathways: Details retinofugal projections via intrinsically photosensitive retinal ganglion cells (ipRGCs) to key brain regions such as the suprachiasmatic nucleus, limbic system, and thalamus.
• Neuroplastic Changes: Elucidates how these pathways induce neuroplastic changes, including hippocampal neurogenesis and synaptic remodeling.
• Integrative Model: Proposes a 'peripheral input-central processing-functional output' model for understanding LT's brain regulation.

Key Findings:

• Cognitive impairment in depression is linked to long-term patient prognosis and functional recovery.
• Light Therapy (LT) is a non-invasive method that shows promise in improving cognitive function in depression.
• LT's mechanisms extend beyond circadian rhythm regulation to include neuroplastic changes in the brain.

Interpretation:

This review provides a framework for understanding how LT can lead to cognitive improvements in depression through specific neural pathways and neuroplasticity.

Limitations:

• Current understanding of LT mechanisms is limited and requires further high-quality randomized controlled trials.
• Existing studies may not fully capture the complexity of the neural circuitry involved.

Conclusion:

This review integrates clinical and basic research evidence to clarify the pathway from retinal projections to neuroplasticity in the context of LT and cognitive function in depression.