Polygala root, also known as Polygala tenuifolia or Yuan Zhi, has a long history of use in Traditional Chinese Medicine (TCM) for supporting the nervous system. Traditionally, it is believed to "calm the spirit," improve memory, and alleviate symptoms associated with anxiety, insomnia, and forgetfulness. In TCM, Polygala root is often included in herbal formulas intended to address "Shen" disturbances, which are related to mental and emotional well-being.

The traditional rationale is based on centuries of empirical observation rather than modern scientific methodologies. Some preclinical studies—mostly in animal models—have investigated the neuroprotective and cognitive-enhancing effects of Polygala tenuifolia, suggesting possible mechanisms such as modulation of neurotransmitter systems, reduction of oxidative stress, and anti-inflammatory effects. However, robust clinical trials in humans are lacking, and the evidence from scientific studies remains preliminary.

Overall, the use of Polygala root to support the nervous system is primarily justified by traditional practice and anecdotal reports rather than well-established scientific validation. The current scientific evidence is insufficient to fully endorse its efficacy, but it does not entirely contradict traditional uses. Therefore, the evidence rating is moderate but relies heavily on historical rather than rigorous modern scientific support.