Design of a testbed for mechanical and thermal stimulation in somatosensory studies

To address the low repeatability and accuracy of traditional technologies for testing the human somatosensory system, this work presents a novel mechatronic testbed. The testbed allows for the delivery of mechanical and thermal stimuli with a high spatial resolution, enabling continuous or discrete stimulation with a small fixed area and in a single experimental session. The testbed was employed to identify the mechanical/thermal innocuous and painful thresholds and the human ability to distinguish the nature of a painful stimulus, on both the hand and the forearm of 12 healthy volunteers. The results demonstrated the capability of the developed testbed to produce a range of forces that can induce different sensations (touch or pain). We found a statistical difference between the innocuous and painful thresholds, regardless of the tested anatomical spot. In this paper, a small thermal stimulation tip was appositely selected to study the reaction to a focused thermal stimulus that has been poorly investigated so far. The results highlighted a statistically significant difference between the two stimulated sites for the cool sensation and the hot pain. Moreover, the painful recognition task was sped up by the use of the developed testbed, which allowed a more fair comparison among the applied stimuli, increasing the accuracy, repeatability, and consistency when compared to the state-of-the art.