A tasty new study analyzing the effects of Szechuan pepper, a commonly used spice in Asian cooking, uncovers the intricate dynamic between the senses of taste and touch, and researchers say their findings could lead to a better understanding of what causes tingling sensations for patients with chronic pain.
Though Szechuan pepper is not actually a pepper - it is the dried berries of a type of ash tree - it is used in many dishes, such as Szechuan chicken stir-fry. The spice is not particularly spicy, but it causes a tingling sensation on the lips.
The researchers, led by Dr. Nobuhiro Hagura of the University College London Institute of Cognitive Neuroscience, applied Szechuan pepper to the lower lip of participants, who were then asked to compare the frequency or vibration of the tingling sensation on their lips with the frequencies of a vibrator on their right index finger.
The results were published in the journal Proceedings of the Royal Society B.
Szechuan pepper, which comes from dried berries, tingled the lips of participants by activating brain-signaling fibers, findings which could help with pain relief one day.
According to the team, an active ingredient in the peppers activates certain RA1 fibers in the lips and tongue, which are responsible for sending touch sensation.
Dr. Hagura says:
"This is the first time that we've been able to show how chemicals activate touch fibers, including a measurable frequency [...] we wanted to find out why Szechuan pepper specifically works on the light-touch fibers, producing a conscious sensation of touch."
Results from the experiment showed that the participants' perception of the tingling frequency was consistently around 50 Hz, which corresponds with the frequency of RA1 fibers.
Dr. Hagura explains:
"What we found was that a unique active ingredient in the pepper, called sanshool, activates these fibers, sending a highly specific signal to the brain. Szechuan peppers and physical touch sensations share this same pathway to the brain."
Additionally, the researchers found that by adapting the RA1 channel with prolonged mechanical vibration, they could also reduce the tingling frequency made by the Szechuan pepper.
They say this confirms that "the frequency-specific tactile channel is shared between Szechuan pepper and mechanical vibration."
Dr. Hagura says they hope that more studies on the tingling sensations brought on by sanshool "could help to clarify the brain processes underlying these sensations, and how they are related to pain in some cases."
Though other products, such as chilli, mustard oil and menthol, can stimulate thermal and pain fibers in the skin, the team would like to investigate further why people like to eat Szechuan pepper, and how touch sensation can affect the taste of food.
Medical News Today recently reported that throbbing pain is surprisingly not linked to our pulse.