We cannot conduct necessary motions in our daily life without touch sense. Touch sense used for manipulating objects, such as handling a needle or grabbing a pencil, is initiated by touch sensory nerves that innervate our skin and recognized through several mechanisms of sensory transduction. While it is well known that touch sense is affected by skin temperature, other physical approaches for affecting touch sense have not fully known. Here we show how touch sense is drastically changed by pressing the proximal phalange of the finger under the condition that blood flow is blocked compulsively to approximately 30 % decrease of normal condition. We found that pressing the finger improves the resolution of pressure sense in touch with approximately 3 times than that before pressing. While it can be naturally expected that continuous pressure eventually results in losing touch sense completely due to necrosis of tissue after all, our results demonstrate that pressing the proximal phalange of the finger temporarily makes a dramatic improvement of touch sense. Furthermore, we confirm that fingertip becomes approximately 20 % harder than that before pressing. This suggests one possible explanation where the contact force tends to stimulate mechanoreceptors through harder finger skin surface. Another possible explanation is that our brain notices the emergency situation and amplifies the sensitivity of the whole nerve system to protect our body. We anticipate our discovery to be a starting point toward more sophisticated neuroscience of our body. Also, this discovery may lead to the development of device for amplifying touch sense by appropriate pressing.
Measuring fingertip stiffness by using non-contact stiffness sensor.
丁憙勇, 金子真, 東森充, 松川寛二: 指根元部圧迫時における指先触感度の向上，計測自動制御学会論文集，第43巻 11号, pp. 973-979, 2007.
H. Jeong, M. Higashimori, and M. Kaneko: Improvement of Touch Sensitivity by Pressing, Proc. of International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC 2008), (Vancouver, British Columbia, Canada, 2008.08.21.), pp. 2409-2414, 2008.