Neuroprosthetics

Sensory feedback is essential. Without it you simply won’t know if you’ve successfully fulfilled a task. Just think you’d be dropping everything.

A recent study in Science Translational Medicine has shown that it is possible to produce realistic sensations in amputees by stimulating the nerves. I guess this could be termed ‘next generation prosthetics’.

We feel the level of pressure applied to our skin based on different neural signal types which are all judged on a single continuum of intensity be it indentation, vibration or texture. Increasing the intensity of stimulation either increases the firing rate of the nerve fibres or recruits more nerve fibres close to the area of touch. In the context of amputees or those with paralysis manipulating sensory intensity is the simplest way of interpreting sensory feedback. Without sensory input amputees are unable to differentiate between a handshake or a crushing force.

The aim of this study was to determine if pulse frequency and pulse width affects the perceived tactile intensity and ability to manipulate objects in two upper limb amputees as well as percieve force. Electrical stimulation was delivered by an external stimulator through percutaneous leads to an interface implanted on the median, ulnar, and radial nerves of an upper-limb amputee. Stimulation consists of different types of pulses delivered to individual contacts in the interface. The interface reshapes the nerve and achieves close proximity between the fascicles and the stimulating contacts, improving selectivity. Each electrode contact evokes sensory percepts on small regions of the missing hand of the subject.

The two subject were able to perceive different intensities tactile sense on their missing hand as well as able to compare the intensity to the pressure applied by mechanical force on their intact hand. This is quite a step forward in the world of prosthetics and could really enable motor skills of amputees.

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