Journal of Rehabilitation Medicine 51-3 | Page 63

J Rehabil Med 2019; 51: 209–216 ORIGINAL REPORT TOUCH ON PREDEFINED AREAS ON THE FOREARM CAN BE ASSOCIATED WITH SPECIFIC FINGERS: TOWARDS A NEW PRINCIPLE FOR SENSORY FEEDBACK IN HAND PROSTHESES Ulrika WIJK, OT, MSc 1 *, Pamela SVENSSON, MSc 2 *, Christian ANTFOLK, PhD 2 , Ingela K CARLSSON, OT, PhD 1 , Anders BJÖRKMAN, MD, PhD 1 and Birgitta ROSÉN, OT, PhD 1 From the 1 Department of Translational Medicine – Hand Surgery, Lund University and Skåne University Hospital, Malmö and 2 Department of Biomedical Engineering, Faculty of Engineering, Lund University, Lund, Sweden *These authors contributed equally to this article. Objective: Currently available hand prostheses lack sensory feedback. A “phantom hand map”, a referred sensation, on the skin of the residual arm is a pos­ sible target to provide amputees with non-invasive somatotopically matched sensory feedback. How­ ever, not all amputees experience a phantom hand map. The aim of this study was to explore whether touch on predefined areas on the forearm can be as­ sociated with specific fingers. Design: A longitudinal cohort study. Subjects: A total of 31 able-bodied individuals. Methods: A “tactile display” was developed consis­ ting of 5 servo motors, which provided the user with mechanotactile stimulus. Predefined pressure points on the volar aspect of the forearm were stimulated during a 2-week structured training period. Results: Agreement between the stimulated areas and the subjects’ ability to discriminate the stimula­ tion was high, with a distinct improvement up to the third training occasion, after which the kappa score stabilized for the rest of the period. Conclusion: It is possible to associate touch on in­ tact skin on the forearm with specific fingers after a structured training period, and the effect persisted after 2 weeks. These results may be of importance for the development of non-invasive sensory feed­ back systems in hand prostheses. Key words: artificial limbs; amputation stumps; sensory feedback; upper extremity. Accepted Dec 20, 2018; Epub ahead of print Feb 27, 2019 J Rehabil Med 2019; 51: 209–216 Correspondence address: Birgitta Rosén, Department of Hand Sur- gery, Skåne University Hospital, SE-205 02 Malmö, Sweden. E-mail: [email protected] L osing a hand is devastating to the individual, with large physical and psychological consequences (1). The loss of sensibility and motor functions is a major problem for the affected individual. Advances in engineering have made it possible to build more advanced hand prostheses with improved grasping alternatives and range of motion (2, 3), but there is no hand prosthesis that is even close to replacing all of the lost functions (1). Control of motor functions in the hand is highly dependent on sensory feedback (4). One LAY ABSTRACT A drawback of currently available hand prostheses is the lack of sensory feedback. Some amputees experience a feeling of touch of the amputated hand when the resi- dual limb is touched. This kind of referred sensation is called “phantom hand map”. However, not all amputees experience “phantom hand map”. Therefore, we exami- ned whether touch on predefined areas on the forearm can be associated with specific fingers in individuals with an intact arm, using a tactile display during a 5-week training period. In conclusion, it is possible to learn to associate touch on predefined areas on the forearm with specific fingers after a structured training period, and the effect persisted after 2 weeks. These results may be of importance for the development of non-invasive sensory feedback systems in hand prostheses. priority in prosthetic design that is desirable among arm amputees is how to provide the user with sensory feedback (2, 3, 5–9). It has been shown that sensory feedback improves grasping control and performance with myoelectric hand prostheses in inexperienced users (10, 11). Both invasive and non-invasive sensory feedback systems are under development (2, 9, 12–19). Following an arm amputation, a phenomenon des- cribed as referred sensation may occur. It is described as an experience of touch of the phantom fingers when touching the skin of the forearm and is herein called a “phantom hand map” (PHM) (20, 21). The PHM is unique for each individual and can differ from 1 or 2 diffusely located areas on the residual forearm with referred sensations, to a very detailed map with several specific areas where touch is experienced as touching the lost hand (20, 21). Furthermore, when touching specific areas in the PHM there is cortical activation in the primary somatosensory cortex (S1), which very closely resembles activation seen after touching the different fingers in an able-bodied subject (22). A non-invasive method for sensory feedback in hand prostheses utilizing the PHM has been presented (23). For non-invasive sensory feedback, a 3-fold process is required; firstly, a registration of the tactile stimuli by sensors is needed, secondly, actuators for transferring the stimuli from the sensors to the user, and thirdly, a process of relearning is necessary with adaptation in This is an open access article under the CC BY-NC license. www.medicaljournals.se/jrm Journal Compilation © 2019 Foundation of Rehabilitation Information. ISSN 1650-1977 doi: 10.2340/16501977-2518