ONE of the few upsides of war is that it often gives technology a boost. A notable beneficiary of this is the science of prosthetic limbs. The various conflicts of the past decade have produced a steady stream of soldiers returning with missing arms and legs, and spurred efforts to improve mechanical replacements for them.

As a result, modern prosthetic limbs can move around much more fluidly, and sport features such as individually controllable fingers. Artificial arms and legs have been developed that are attached to the severed nerves in an amputee’s stump, and can thus be moved the way natural limbs are, simply by thinking about it. Scientists have even made some progress in the other direction—transmitting sensory information from a prosthesis back to a user’s brain.

The most impressive example so far is described in a paper in Science Translational Medicine, in which Stanisa Raspopovic of the BioRobotics Institute at the Scuola Superiore Sant’Anna, in Pisa, and his colleagues explain how they built an artificial hand that can transmit the sensation of touch back to its user’s brain. After a series of laboratory tests, they report that their volunteer—Dennis Aabo Sorensen, a 36-year-old Dane who lost his hand nine years previously—was able to use that feedback to accomplish the sort of delicate tasks that wearers of artificial limbs often struggle with.

Dr Raspopovic used a prosthetic hand with built-in pressure sensors. It was hooked up to Mr Sorensen’s nervous system through electrodes implanted in his arm in places where they were able to stimulate the ulnar and median nerves, which between them innervate much of an ordinary hand. The readouts from the hand’s sensors were processed by a computer, which then fed tiny jolts of electricity into the electrodes.

After a bit of calibration, Mr Sorensen reported feeling a sensation of touch in the thumb, index finger and little finger of his newly installed hand. That allowed him to do things most wearers of prosthetic hands cannot, such as easily picking up delicate objects without crushing them. The wearer of a more old-fashioned hand would need to do this slowly and by eye, and even then might fail.

Mr Sorensen, by contrast, could do it blindfolded and wearing ear mufflers. In more than 700 trials he was able to use the sensory information from his new hand to calibrate his grip to a range of tasks. In one, in which he had gradually to tighten and then loosen his grip, the bionic hand performed almost as well on the tightening stage as his other, biological hand (its performance was less impressive when he was loosening his grip). And although he was receiving information from only three parts of it, that was enough to let him tell the difference by feel alone between a lump of wood, a stack of plastic cups and a pack of cotton balls.

To owners of biological hands, this level of feedback may seem a bit crude. But that says as much about the elegance and sophistication of the flesh-and-blood version as it does about the limitations of its mechanical replacement. And, given the pace at which the field is moving, the technology is likely to get better—fast.