Restoration of sensory information via bionic hands

Abstract

Individuals who have lost the use of their hands because of amputation or spinal cord injury can use prosthetic hands to restore their independence. A dexterous prosthesis requires the acquisition of control signals that drive the movements of the robotic hand, and the transmission of sensory signals to convey information to the user about the consequences of these movements. In this Review, we describe non-invasive and invasive technologies for conveying artificial sensory feedback through bionic hands, and evaluate the technologies' long-term prospects.

Fig. 1 |. Technologies for restoring sensory feedback via bionic hands.

a, Non-invasive sensory feedback. The output of sensors on the bionic hand drives mechanical or electrical stimulation of the skin to convey information about contacted objects, in this case through stimulators housed in an armband. b, Sensory feedback via an electrical interface with the peripheral nervous system. Sensors on the bionic hand drive the electrical stimulation of a nerve to elicit sensations referred to the phantom hand. c, Sensory feedback via an interface with the central nervous system. Sensors on the bionic hand drive the electrical stimulation of the central nervous system to elicit sensations referred to the de-afferented hand. Credit: Image courtesy of Kenzie Green

Fig. 2 |. Somatotopic mapping following targeted reinnervation.

a, Stimulation of different patches of skin on the stump evokes sensations referred to different digits. The mapping can in principle be exploited to achieve tactile feedback that is more intuitive. b, Mechanical stimulation of the chest, to which nerve fibres have been rerouted. The stimulation elicits sensations referred to the phantom limb, and often to the phantom hand. Credit: Image courtesy of Kenzie Green; panels adapted with permission from ref. , Foundation of Rehabilitation Information (a) and ref. , Elsevier (b)

Fig. 3 |. Examples of non-invasive stimulation.

a, Array of coin motors used to deliver vibrotactile feedback. b, Configuration of a combination of electrotactile and vibrotactile stimulators. Credit: Image courtesy of Kenzie Green; panels adapted with permission from ref. , IEEE (a) and ref. , IEEE (b)

Fig. 4 |. The somatosensory periphery.

a, The different types of low-threshold cutaneous mechanoreceptors that innervate the palmar surface of the hand. Clockwise from top left: Meissner corpuscle, Ruffini ending, Merkel disk and Pacinian corpuscle. b, The hand is innervated by the median nerve (blue), the ulnar nerve (light green) and the radial nerve (purple). c, Nerves are divided into individual bundles of fibres (known as fascicles). Credit: Image courtesy of Kenzie Green

Fig. 5 |. Electrical interfaces with the peripheral nerves.

The panels show three examples of chronically implanted interfaces. a, The flat interface nerve electrode. b, The transverse intrafascicular multichannel electrode. c, The Utah slant electrode array. d, The schematic indicates how the three electrode arrays interact with the nerve. Credit: Image courtesy of Kenzie Green

Fig. 6 |. Projected fields for nerve stimulation.

The electrical stimulation of the residual somatosensory nerves of an amputee evokes localized and stable percepts on the missing hand. Stimulation through different electrodes located on the median (blue), ulnar (green), and radial (red) nerves over the course of two months led to consistent perceived sensations on the phantom hand (the locations are indicated by the coloured patches). Credit: Image courtesy of Kenzie Green; adapted with permission from ref. , AAAS

Fig. 7 |. Electrical interfaces with the central nervous system.

a, Possible loci of neural interfaces for the restoration of touch in the central nervous system. From bottom to top: the cuneate nucleus, the thalamus and the somatosensory cortex. The insets indicate the arm and face regions of the somatosensory homunculus in the human somatosensory cortex (top left), and the cortical fields in the Brodmann’s areas 3a, 3b, 1 and 2 of the somatosensory cortex (top right). b, Surgical image showing the implantation, in a human, of two arrays in the motor cortex (anterior to the central sulcus; left) and of two arrays in the somatosensory cortex (posterior to the central sulcus; right). The coloured areas indicate the mapping of the palm, thumb, index finger and little finger in the somatosensory cortex. The symbol ‘Ω’ indicates the presumptive location of the hand in the motor cortex (the so-called ‘hand knob’). Credit: Image courtesy of Kenzie Green; adapted with permission from ref. , AAAS