BCIs have deep roots. In the 18th century Luigi Galvani discovered the role of electricity in nerve activity when he found that applying voltage could cause a dead frog’s legs to twitch. In the 1920s Hans Berger used electroencephalography to record human brain waves. In the 1960s José Delgado theatrically used a brain implant to stop a charging bull in its tracks. One of the field’s father figures is still hard at work in the lab.

Eberhard Fetz was a post-doctoral researcher at the University of Washington in Seattle when he decided to test whether a monkey could control the needle of a meter using only its mind. A paper based on that research, published in 1969, showed that it could. Dr Fetz tracked down the movement of the needle to the firing rate of a single neuron in the monkey’s brain. The animal learned to control the activity of that single cell within two minutes, and was also able to switch to control a different neuron.

Dr Fetz disclaims any great insights in setting up the experiment. “I was just curious, and did not make the association with potential uses of robotic arms or the like,” he says. But the effect of his paper was profound. It showed both that volitional control of a BCI was possible, and that the brain was capable of learning how to operate one without any help.

Some 48 years later, Dr Fetz is still at the University of Washington, still fizzing with energy and still enthralled by the brain’s plasticity. He is particularly interested in the possibility of artificially strengthening connections between cells, and perhaps forging entirely new ones.

As an example, he points to research in which the recording of an action potential in the brain prompts not only the normal firing of a motor neuron in the spinal cord but also a parallel stimulus from a BCI delivered to the same site. The idea is to take advantage of a relationship made famous in an aphorism by a Canadian psychologist, Donald Hebb: “Neurons that fire together, wire together.” This reinforced stimulus strengthens the connection between the original action potential and the motor neuron, which could help recovery from spinal-cord injuries. Such stimulation might also encourage stronger bonds in the brain itself—between the speech-processing area of a stroke victim’s brain, say, and the region that controls movements of the lips and mouth.

Asked to explain the slow rate of progress since his breakthrough paper, Dr Fetz points to the technical difficulties of recording from single cells and the high hurdle to doing this sort of work in people. But he does not think there is a need to find out much more about the brain in order to make further advances: “I have had a lot of progress by just jumping in.”