Effects Of Electrode Size And Spacing On Sensory Feedback Using Transcutaneous Electrical Nerve Stimulation

Amputees will lose both motor and sensory function after amputation,which seriously affects their daily lives and devastates life qualities.Many kinds of prosthetic limbs or hands on the market have been developed to help amputees partially restore the missing motor function.However,due to lack of sensory feedback,dexterous manipulation of the state-of-the-art prosthetic hands is hard to be achieved,which inevitably limits the wide acceptance clinically for the upper-limb amputees.Tactile sensory feedback plays a key role in accomplishing the dexterous manipulation,and the non-invasive transcutaneous electrical nerve stimulation(TENS)of the evoked tactile sensation(ETS)area would be an effective way to realize sensory feedback clinically.In order to realize the high-spatial-resolution tactile sensory feedback in the evoked tactile sensation region,we investigated the effects of electrode size and spacing on the tactile sensations for potentially optimizing the surface electrode array configuration.Six forearm-amputated subjects were recruited in the psychophysical studies.With the diameter of the circular electrode increasing from 3 mm to 12 mm,the threshold current intensity was enhanced correspondingly under different sensory modalities.The smaller electrode could potentially lead to high sensation spatial resolution.Whereas,the smaller the electrode,the less the number of sensory modalities.For an Φ-3 mm electrode,it is even hard for the subject to perceive any perception modalities under normal stimulating current.In addition,the two-electrode discrimination distance(TEDD)in the phantom thumb perception area decreased with electrode size decreasing in two directions of parallel or perpendicular to the forearm.No significant difference of TEDD existed along the two directions.Studies in this paper would guide the configuration optimization of the TENS electrode array for potential high spatial-resolution sensory feedback.We also designed and processed flexible multi-channel microelectrode array using MEMS technology for potential application of the transcutaneous electrical nerve stimulation in the evoked tactile sensation area.