Study on lower back electrotactile stimulation characteristics for prosthetic sensory feedback

Aiming at the seamless integration of artificial limbs into the human body, sensory feedback plays an important role. There are two main methods of providing sensory feedback: invasive and non-invasive. One of the challenges of non-invasive methods is to identify the appropriate body location to transmit information through. In prosthetic applications it makes sense to target locations with low sensory loads. However, this presents new challenges to overcome due to the low mechanoreceptor density of these areas. In this study we aim to understand the limitations of using electrical stimulation for transmitting information to the body by targeting the lower back. We investigate the effects of (1) stimulation frequency and (2) electrode size on the stimulation parameters for sensation. Our results show an increased influence of stimulation frequency over the stimulation parameters with smaller electrodes. Larger electrodes reduced inter-individual differences, however the stimulation range, that is the difference between the lower sensation threshold and the pain threshold, was considerably reduced. Our experiments show that the current required to achieve nerve depolarization was low (2mA to 10 mA).