Chinese spice gives us an insight into how human brains detect and perceive rubbing

A new insight into how human brains detect and perceive different types of rubbing, such as flower vibrations and constant pressures, has been unveiled by UCL scientists with the help of an ancient Chinese culinary ingredient, Szechuan pepper .

There are many different types of receptor cells in the skin that allow us to sense different types of rubbing. For more than a century, scientists have been figuring out whether rubbing signals from all types of receptors are independently processed by the brain, or whether these different signals interact. work before they reach consciousness.

For the study, published in Proceedings of the Royal Society B., UCL researchers took a new approach to this issue by chemically inducing one type of friction receiver, and another type mechanically. This avoids the problem of various mechanical friction stimuli that may interact within the skin, with unknown effects on the receptors.

Instead, the UCL team used hydroxy-α-sanshool, a bioactive blend of Szechuan pepper responsible for the normal tingling quality of Szechuan food, to stimulate the friction receptors that are responsible for flow-sensing vibration sensitivity.

In the study, which involved 42 participants, hydroxy-α-sanshool was applied to a small skin area on the lip. As soon as participants began to experience a tingling sensation, they were asked to notice the strength of the tingling sensation.

The next stimulus researchers applied constant pressure to different areas of the upper and lower lips. Participants described their subjective understanding of the intensity of the tingling sensation, by evaluating it compared to the first feeling before stress was applied.

Over several experiments, the tingling sensation caused by hydroxy-α-sanshool, was significantly reduced by constant pressure. The intensity of tingling sensation caused by hydroxy-α-sanshool decreased as the constant pressure increased, and also decreased as the site of constant pressure was moved closer to the site where sanshool was placed. engaged.

Scientists have previously said how ‘massage prevents pain’, but our work provides groundbreaking evidence that one type of massage can prevent another type of massage.

Our findings suggest that the friction system for constant pressure must inhibit the friction system for flow vibration at some point in the nervous system.

The inhibition between these signals may explain how the brain perceives a single perception of friction, despite the wide range of signals transmitted by the different types of sensory receptors in the brain. skin. “

Professor Patrick Haggard, Lead author, UCL Institute of Cognitive Neuroscience