Fetz et al.1 implanted a 'Neurochip', which had a recording microelectrode (Nrec) and a stimulating microelectrode (Nstim), in the motor cortex of a monkey. a, Using a technique called intracortical microstimulation (ICMS), they passed a series of electric pulses into the cortex next to the two Neurochip electrodes and at a control region to map the muscle responses at the monkey's wrist. The right panel shows the wrist torque produced by ICMS, with the arrows showing the mean trajectory. b, The next step was a conditioning period, when the Neurochip recorded the activity of a single neuron in the cortex. Every time there was an activity spike in that neuron, the Neurochip sent an electrical pulse through the stimulating microelectrode into another neuron. c, After 24 hours of conditioning, the ICMS response was measured again. The response produced by ICMS near the Neurochip recording site had changed towards that produced near the Neurochip stimulation site, showing that the neural circuit had been partially rerouted by conditioning.