Periodic Reporting for period 3 - ARTTOUCH (Generating artificial touch: from the contribution of single tactile afferents to the encoding of complex percepts, and their implications for clinical innovation)
Berichtszeitraum: 2022-01-01 bis 2023-06-30
How do the receptors in your skin respond to the touch of silk or a drop of rain? Our touch system plays an essential role in how we discriminate between different surfaces and objects, which allows us to interact effortlessly with our surroundings. We readily distinguish between a vast range of solid textures, from fine hairs to polished surfaces, as well as between different liquids, via complex percepts like wetness, stickiness, and oiliness. This is enabled by highly precise input from different types of mechanoreceptors in the skin that respond in specific ways to touch. If this system is interrupted, interacting with the world becomes problematic. In somatosensory disease or body injury, such as peripheral neuropathy or amputation, the consequences are dramatic on the quality of life. The current project aims to understand how touch is encoded in humans: from fundamental signals in single touch receptors in the skin, to the generation and perception of complex sensations. These insights will help in elucidating the causes and treating the symptoms of somatosensory disorders. Furthermore, applying the knowledge for the provision of realistic sensory feedback in prosthetics represents a great advancement in terms of individual and social usage of a prosthetic device, allowing far more naturalistic interactions and increased embodiment. Overall, Project ARTTOUCH has two main objectives: (i) to use electrical stimulation in human nerves to activate a single nerve fiber and produce artificial sensations that can be quantified perceptually and through using neuroimaging and (ii) to investigate how touch of complex surfaces is encoded and perceived, such as when interacting with different textures and liquids. These results provide exquisite insights into the human touch system and how it works in everyday life, where we easily feel differences in textures, surfaces, and even small drops of rain. The end aim of the project is to provide information on how these precise sensations are generated to then re-inject this input artificially, via electrical stimulation into nerves in amputees with a prosthetic device, to provide real-time, sensory feedback during prosthetic touch.
The ARTTOUCH project aims to uncover how basic touch is encoded by the skin and represented centrally in the brain, as well as how more complex sensations are generated, such as wetness and tactile pleasantness. To achieve this, the project uses a specialist technique that is only conducted few groups in the world, namely, microneurography. This allows us to access human peripheral nerves, such as the nerves in the hand, and record from a single nerve fiber that receives information from a receptor in the skin. In healthy humans, a small needle electrode is inserted into the skin and into a nerve, to record the responses to touch. We ask the human participant to touch different textures and surfaces, then we record the responses from different touch receptors (mechanoreceptors). We have found that when a person actively touches a surface, distinct properties of the surface and movement are encoded by different types of mechanoreceptor. Further, when we apply drops of water to the skin, we find that only the most sensitive mechanoreceptors respond and these encode the vibration of the drop on the skin. We also use an extension of the technique of microneurography, where we can record from a single touch fiber and then artificially stimulate it via re-injecting a small electrical current. This produces a very small point of touch, which differs depending on the mechanoreceptor stimulated. For example, one type produces vibration and another the sensation of pressure. We have found that human participants can discriminate between small differences in trains of electrical stimulation injected into a single fiber and we have also mapped the responses generated from this in the brain. We have presented this work in online talks and conferences, and we will publish the results via journal papers soon.
The ARTTOUCH project offers a new and novel approach to studying how touch is encoded and perceived. It is beyond state-of-the-art, where cutting-edge equipment is being developed and used to probe the workings of the human touch system. This allows us to gain unrivalled insights into how humans sense different solids and liquids, as well as providing new technology to help in diagnosing somatosensory disorders and to stimulate human nerves to provide sensory feedback in prosthetics for amputees. We expect to publish new results on the precise workings of the human touch system, where we will show how single touch receptors in the skin (mechanoreceptors) respond to different types of textures, surfaces, and liquids, including when we actively touch a surface. Novel investigations will be conducted in humans to probe these mechanisms, including peripheral recordings from human nerves (microneurography) and nerve stimulation, combined with advanced brain imaging and behavioral experiments. These ambitious and ground-breaking approaches will provide unrivalled and detailed information about human touch that can be applied to medicine and prosthetics. We aim to show how humans encode and perceive drops of water, which has been little-explored, yet we encounter liquids all the time in our everyday lives. Humans do not have any receptor in the skin for wetness (hygroreceptor), thus combinations of touch and temperature stimuli will be explored to understand both how the skin encodes wetness and how the brain interprets and perceives it.