Our sense of touch is essential to explore our environment and experience life and is based on signals from receptors in the body that are sensitive to different types of stimulation. The TACTHUM projects aims to investigate the fundamental firing of mechanoreceptors in the body to various external stimuli, with an end-aim to better understand the human somatosensory system and to apply this knowledge to provide comprehensive sensory feedback in prosthetics. We have a vast system of peripheral receptors in the skin and muscles that provide us with exquisitely detailed information about our everyday interactions. When there is injury to a body part, such as in amputation, there is a significant loss of somatosensory input. Prosthetic devices have greatly developmed in the past few years, especially with the introduction of useful sensory feedback. However, there is a lot to discover both about the workings of the somatosensory system and how to recreate this to give feedback in a prosthetic device.

The main objective of the TACTHUM project is to understand how to recover and apply useful somatosensory feedback in prostheses for amputees. There are a number of other sub-objectives, to:

1. Determine how tactile mechanoreceptors encode the texture of natural surfaces during passive and active exploration.
2. Investigate how our sense of touch varies with emotional state.
3. Explore what happens to our sense of touch when we explore surfaces at different temperatures.
4. Understand the origin of our perception of humidity.
5. Investigate differences in the encoding of tactile information with age.
6. Determine the perceptions generated by the stimulation of single tactile afferents.
7. Study changes in spontaneous activity and responses to tactile stimulation on the residual limb of amputees.

To accomplish these objectives, we will primarily use the technique of microneurography, in vivo recordings from peripheral nerves, to gain direct information about the firing of peripheral neurons in humans. In conjunction with this, we will use a variety of mechanical and thermal stimuli to excite somatosensory fibers and register the activity of other physiological and perceptual measures. This will allow us to gain a fuller understanding of how the incoming somatosensory signals are interpreted and processed. Overall, we aim to explore how more naturalistic tactile interactions are encoded and how these can be translated to provide realistic prosthetic feedback.

Inclusion Criteria:

• Men and women aged between 20 and 70.
• Be a member of a social security scheme, or a beneficiary of such a scheme
• Be calm enough to sit still for four hours.
• Specific for people participating in Arm 7 on amputees: People with an upper or lower limb amputation (unilateral) of more than 2 years.

Exclusion Criteria:

• Have peripheral neuropathy (diabetes, Raynaud's disease) or chronic muscle and/or sensory pain.
• Have a neurological or psychiatric history.
• Be subject to epilepsy.
• Be pregnant (declared) or breastfeeding, having given birth within the last year.
• Be afraid of injections.
• Being under dermatological treatment.
• Have a pacemaker.
• Not being able to understand the information leaflet and the consent form or sign it.
• Be subject to a legal protection measure (declarative)
• Be a protected adult (curatorship or guardianship)