Touch on predefined areas on the forearm can be associated with specific fingers: Towards a new principle for sensory feedback in hand prostheses

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 residual limb is touched. This kind of referred sensation is called "phantom hand map". However, not all amputees experience "phantom hand map". Therefore, we examined 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. Objective: Currently available hand prostheses lack sensory feedback. A "phantom hand map", a referred sensation, on the skin of the residual arm is a possible target to provide amputees with non-invasive somatotopically matched sensory feedback. However, 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 associated with specific fingers. Design: A longitudinal cohort study. Subjects: A total of 31 able-bodied individuals. Methods: A "tactile display" was developed consisting 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 stimulation 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 intact 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 feedback systems in hand prostheses.

Development and Testing of a Wearable Vibrotactile Haptic Feedback System for Proprioceptive Rehabilitation

“…This study also verifies the assumption made by Wijk et al [30] that the training time, for associating predefined points on arm with fingers, in amputees as compared to able-bodies subjects should be less. In the study, with able-bodied subjects [30], it took approx.…”

“…This study also verifies the assumption made by Wijk et al [30] that the training time, for associating predefined points on arm with fingers, in amputees as compared to able-bodies subjects should be less. In the study, with able-bodied subjects [30], it took approx. 20 minutes to complete the training session for one activity, as compared to this study with amputees where the maximum duration for training session of an activity is 10 minutes.…”

“…In a recent, first of its kind study [30], this concept was explored by associating active locations on the forearm with specific fingers, using mechanotactile stimuli. Although the concept was practically verified but one major disadvantage of the system was that it was bulky owing to the five servo motors and thus did not qualify as a wearable system.…”

Sensory Feedback in Hand Prostheses: A Prospective Study of Everyday Use

“…Results from a fMRI study showed that stimulation of the finger areas in the PHM on the residual arm activated the same areas in the primary somatosensory cortex as stimulation of the fingers in an able-bodied control group ( Bjorkman et al, 2012 ). Not all amputees experience a PHM ( Ehrsson et al, 2008 ), but touch on predefined areas on the forearm can be learned to be associated to specific fingers ( Wijk et al, 2019 ).…”

“…Results from a fMRI study showed that stimulation of the finger areas in the PHM on the residual arm activated the same areas in the primary somatosensory cortex as stimulation of the fingers in an able-bodied control group (Bjorkman et al, 2012). Not all amputees experience a PHM (Ehrsson et al, 2008), but touch on predefined areas on the forearm can be learned to be associated to specific fingers (Wijk et al, 2019). Antfolk et al (2012Antfolk et al ( , 2013a have earlier presented a noninvasive sensory feedback concept utilizing the PHM that is also somatotopically matched as well as modality matched, regarding pressure (Antfolk et al, 2012(Antfolk et al, , 2013a.…”