Institute of Neuroscience, COSY
Institute of Information and Communication Technologies, Electronics and Applied Mathematics, INMA
The skin is endowed with a rich set of sensors that make it extraordinarily sensitive to contact. This capacity is of enormous importance in the establishment of the relationship between our minds and the outside world. The soft skin of vertebrates is likely to have evolved to efficiently detect the many types of complex, time-evolving mechanical effects that take place during any type of activity such as holding objects or deciding of their nature. The study was focused on the cuneate nucleus of the brainstem, which acts as a hub for all tactile information passing from the skin to the cortex. These neurons, surprisingly, turned out to perform intricate treatment of tactile information. This finding could have important implications in the prevention and treatment of health conditions related to trauma of the spinal cord, limb amputation remediation, aging, and suggests new methods for the design of haptic interfaces for use in virtual reality.
Humans cleverly manage to adapt their fingertip forces to the nature of a manipulated object in including the friction at digit-object interfaces. Neurophysiological as well as behavioral evidence will be presented in this lecture to demonstrate that this ability depend on tactile information and that digit-specific mechanisms are overt within as little as 100 ms after initial object contact.
Our sense of touch is essential in everyday life. It enables us to execute fast and accurate manipulations with our fingers. The loss of tactile sensations severely impairs these capabilities. Tactile information relies on thousands of sensors, called mechanoreceptors, distributed all over the skin surface. These mechanoreceptors act as transducers, i.e., they convert mechanical stresses into electrical signals that are transmitted to the central nervous system. The hands and fingers are the source of most tactile interactions and contain a high density of these sensors. To better understand how the tactile system works, it is crucial to understand the properties of the signals produced by the mechanoreceptors and to relate them to the mechanics taking place in the skin. In this thesis, methods were developed to measure the deformations of the fingertip skin during precisely controlled stimulations mimicking tactile interactions of everyday life. In a first part, vibrations resulting from the active exploration of textured surfaces with the fingertip were recorded in the forearm, showing that these vibrations travel along the hand and forearm and can be sensed far away from the contact point. In the second part, we described contact changes and strains taking place in the skin at the interface between the finger and the contact during the onset of a slip. These measurements provide an insight on the information available at the contact region during object manipulation. In the third part, we recorded fingertip afferent neuron responses to similar stimuli and showed a specific response of some neurons to the slips taking place in the contact area. In all three parts, our results provide useful information for the design of sensory prostheses and tactile displays.