The coding of tactile exploration by skin and muscle afferents using microneurography in humans
Rochelle Ackerley. From: University of Gothenburg, to: Aix-Marseille University, France.
How does touch shape our actions? The aim of the proposal is to investigate the naturalistic behaviour involved during tactile exploration. A unique and novel approach will be used to record from human nerves during self-generated, active touch. The electrophysiological technique of microneurography allows axonal recordings from single afferents in awake, healthy humans. Laboratories from the University of Gothenburg, Sweden and Aix-Marseille University, France have used this technique to study tactile and muscle afferents, respectively, for more than 30 years each. The current project will bring together the expertise from these laboratories to explore how tactile and muscle afferents alter their firing patterns during active touch using the hands; something that has not previously been attempted. We hypothesise that different afferents will show specific modulations to both the surface being touched and the goal of the movement (e.g. to assess whether the surface is rough, pleasant or sticky). The will generate physiological data that represents neuronal responses during natural touching behaviour, whereas previous studies have always applied passive stimulation. This approach will advance the field of sensorimotor control to give unrivalled information about the integration of tactile and muscle input during exploratory touch. The resulting conclusions are useful in rehabilitative medicine, such as the restoration of sensations in amputees. In understanding how the healthy system works, it is possible to apply these ideas and strategies in incorporating real-time feedback in prostheses through intra-neural stimulation of afferents, using the natural firing patterns.
Project Summary Results
The present work aimed to investigate the precise signals from touch (mechanoreceptive) and muscle afferents that provide feedback during movements and tactile interactions. A unique and novel approach was used to record from these human nerve fibres, using the technique of microneurography, which was conducted in laboratories from the University of Gothenburg, Sweden and Aix-Marseille University, France. The current project brought together the expertise from these laboratories to explore how tactile and muscle afferents work to provide sensory feedback to the brain during movement and self-generated, active tactile explorations. The findings include research showing that, during active exploration, different mechanoreceptive afferents encode specific parts of the tactile interaction. Two types of afferents were found to encode interactions involving sticking and sliding movements, while two other types of afferent were found to signal the onset of touch and stretching of the skin. During this active touch, the subjects also adapted their behaviour to the task, where they used different types of movements to touch materials if they were given a specific instruction. Further, it was found that muscle afferents fire more dynamically when the subject was placed in a higher-emotion situation. The project has generated physiological and behavioural data that represents neuronal responses during exploratory behaviour, which has never been conducted previously, but provides unique insights into real-time, human behavioural interactions. The findings can be applied to the restoration of realistic sensations in amputees, where understanding how the healthy system works can be applied to generating useful, artificial feedback signals in amputees using a prosthetic.