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Summary: Japanese researchers have discovered how the astringent “bite” of cocoa flavanols can activate the brain, although little of the compound enters the bloodstream. In mice, the sensation of astringency triggered sensory nerves that stimulated neurotransmitters related to motivation, alertness and memory.
The brain’s norepinephrine network was activated, producing beneficial stress-like physiological responses similar to those of exercise. The findings suggest that the sensory impact of flavanols (not just their absorption) may help explain how foods like chocolate and berries sharpen concentration and improve brain health.
Key facts
Sensory signaling: The astringent taste of flavanols directly stimulates sensory nerves, activating the brain’s norepinephrine network. Exercise-like response: Flavanols induced mild stress responses that improved attention, learning, and memory in mice. New nutritional knowledge: Findings support the concept of “sensory nutrition,” where taste-driven signals influence brain and body function.
Source: Shibaura Institute of Technology
Astringency is a dry, wrinkled, rough or sandpaper-like sensation in the mouth caused by plant-based polyphenols. Polyphenols, including flavanols, are well known to reduce the risk of cardiovascular disease. Flavanols, found in abundance in cocoa, red wine and berries, are associated with improved memory and cognition, as well as protection against neuronal damage.
Despite these benefits, flavanols have poor bioavailability (the fraction that actually enters the bloodstream after ingestion). This has left an important knowledge gap: how can flavanols influence brain function and the nervous system when so little is absorbed?
In response to this challenge, a research team led by Dr. Yasuyuki Fujii and Professor Naomi Osakabe from Shibaura Institute of Technology, Japan, investigated how flavanols affect the nervous system through sensory stimulation.
The study, available online September 11, 2025 and published in volume 11 of the journal Current Research in Food Science, tested the hypothesis that the astringent taste of flavanols can act as a direct signal to the brain.
“Flavanols exhibit an astringent taste. Our hypothesis is that this taste serves as a stimulus, transmitting signals directly to the central nervous system (comprising the brain and spinal cord).
“As a result, flavanol stimulation is thought to be transmitted through sensory nerves to activate the brain, subsequently inducing physiological responses in the periphery through the sympathetic nervous system,” explains Dr. Fujii.
The researchers conducted experiments on 10-week-old mice, administering flavanols orally at doses of 25 mg/kg or 50 mg/kg body weight, while control mice received only distilled water. Behavioral tests showed that flavanol-fed mice exhibited greater motor activity, exploratory behavior, and better learning and memory compared to controls. Flavanols improved neurotransmitter activity in several brain regions.
Dopamine and its precursor levodopa, norepinephrine and its metabolite normetanephrine were elevated in the locus coeruleus-norepinephrine network immediately after administration. These chemicals regulate motivation, attention, stress response, and arousal.
Furthermore, enzymes critical for norepinephrine synthesis (tyrosine hydroxylase and dopamine-β-hydroxylase) and transport (vesicular monoamine transporter 2) were upregulated, strengthening the signaling capacity of the noradrenergic system.
Additionally, biochemical analysis revealed higher urinary levels of catecholamines (hormones released during stress), as well as increased activity in the hypothalamic paraventricular nucleus (PVN), a brain region central to stress regulation. Flavanol administration also increased the expression of c-Fos (a key transcription factor) and corticotropin-releasing hormone in the PVN.
Together, these results demonstrate that flavanol intake can trigger a wide range of physiological responses similar to those induced by exercise, functioning as a moderate stressor that activates the central nervous system and improves attention, arousal and memory.
“The stress responses elicited by flavanols in this study are similar to those elicited by physical exercise. Therefore, moderate intake of flavanols, despite their poor bioavailability, can improve health and quality of life,” says Dr. Fujii.
These findings have potential implications in the field of sensory nutrition. In particular, next-generation foods can be developed based on the sensory properties, physiological effects and palatability of foods.
Funding: This work was supported by JSPS KAKENHI (grant number 23H02166).
Key questions answered:
A: Its astringent flavor acts as a sensory stimulus, directly activating brain pathways.
A: Neurotransmitters such as dopamine and norepinephrine increase, increasing alertness and motivation.
A: It reveals a new mechanism—flavor-based neural activation—that could inspire smarter, brain-targeted food design.
About this neuroscience research news
Author: Kohei Tsuchiya
Source: Shibaura Institute of Technology
Contact: Kohei Tsuchiya – Shibaura Institute of Technology
Image: Image is credited to Neuroscience News.
Original research: Open access.
“Astringent flavanol activates the locus-noradrenergic system, regulating neurobehavior and autonomic nerves” by Yasuyuki Fujii et al. Current research in food science
Abstract
The astringent flavanol activates the locus-noradrenergic system, regulating neurobehavior and autonomic nerves.
Astringency is a characteristic exhibited only by a limited number of polyphenolic compounds that show high electrochemical activity and are susceptible to oxidation under neutral pH conditions, such as the oral cavity and small intestine.
Large-scale intervention studies have shown that the astringent flavanol (FL) can restore hippocampal-dependent memory. However, due to the low bioavailability of FLs, the mechanism of action is still unclear.
In this study, we aimed to elucidate the mechanism by which FLs act on the nervous system through the gastrointestinal tract. After a single dose of FL to mice, spontaneous motor activity in the open field was improved and short-term memory was improved in the novel object test.
At the same time, activation of stress response systems was also observed, such as the sympathetic-adrenal-medullary axis (increased urinary catecholamines) and the hypothalamic-pituitary-adrenal axis (increased corticotropin-releasing hormone mRNA in the paraventricular nucleus).
Using mass imaging and in situ hybridization analyses, high-intensity norepinephrine (NA) was revealed from the locus coeruleus (LC) in the hypothalamus and brainstem immediately after FL administration.
These NA changes have been suggested to be the cause of increased memory, arousal, and sympathetic activity. Furthermore, an increase in NA was observed in the nucleus accumbens in response to visceral sensations induced by oral administration of FL.
The current findings highlight how FL astringent stimulants can activate brain function and the autonomic nervous system through gastrointestinal stimulation, causing physiological changes.
These insights suggest that the sensory properties of foods are important for maintaining homeostasis and promoting human health.
