Polyphenols are the most prevalent naturally occurring phytochemicals in the human diet and range in complexity from simple molecules to high-molecular-weight polymers. They have a broad range of chemical structures and are generally categorized as "neuroprotective," "anti-inflammatory," and "antioxidant" given their main function of halting disease onset and promoting health. Research has shown that some polyphenols and their metabolites can penetrate the blood-brain barrier and hence increase neuroprotective signaling and neurohormonal effects to provide anti-inflammatory and antioxidant effects. Therefore, multi-targeted modulation of polyphenols may prevent the progression of neuropsychiatric disorders and provide a new practical therapeutic strategy for difficult-to-treat neuropsychiatric disorders. Therefore, multi-target modulation of polyphenols has the potential to prevent the progression of neuropsychiatric disorders and provide a new practical therapeutic strategy for such nervous system diseases. Herein, we review the therapeutic benefits of polyphenols on autism-spectrum disorders, anxiety disorders, depression, and sleep disorders, along with in vitro and ex vivo experimental and clinical trials. Although their methods of action are still under investigation, polyphenols are still seldom employed directly as therapeutic agents for nervous system disorders. Comprehensive mechanistic investigations and large-scale multicenter randomized controlled trials are required to properly evaluate the safety, effectiveness, and side effects of polyphenols.

Alzheimer's disease (AD), which is characterized by the development of β-amyloid plaques and neurofibrillary tangles in the brain parenchyma, can result in synaptic and neuronal loss. Clinical signs, including deteriorating memory deficiency, may lead to catastrophic effects for the elderly. Research on brain imaging and its application in the study of AD has advanced extraordinarily over the past 30 years. However, widely used imaging methods are only capable of identifying structural or metabolic alterations at the anatomical level in the brain and can only be utilized for drawing inferential distinctions. As a disease with a complex pathophysiological mechanism, AD has many different molecular pathological features and molecular biomarkers. Therefore, molecular imaging for AD pathology indicators provides a practical method for the early diagnosis and impartial assessment of AD. The present review discusses the pathogenesis of AD, as well as the detection methods and principles of molecular imaging, such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT) techniques. Meanwhile, various tracers and probes applied in molecular imaging that detect Aβ deposits, tau protein accumulation, and neurotransmitters are also reviewed. Molecular pathological tracers provide the possibility to accurately quantify brain changes through molecular imaging.