Podcast with Eberhard Fetz on brain-computer interface and neurochip

Can a monkey learn to control a single neuron in its motor cortex independently of the muscles it normally drives? Eberhard Fetz traces five decades of work on volitional neural control from biofeedback to brain-computer interfaces.

Subscribe for more from the Convergent Science Network podcast series.

Eberhard Fetz recounts the intellectual journey from his pioneering 1969 experiments on operant conditioning of single motor cortex neurons to the development of the Neurochip, an autonomous neural interface that creates artificial connections between brain sites, spinal cord, and muscles. His early work demonstrated that monkeys could learn to volitionally increase or decrease the firing rate of individual neurons to earn rewards, with the key insight that the animal was not simply conditioning a neuron in isolation but learning to control the pattern of activation flowing through a fixed circuit in novel ways.

A central theme is the remarkable flexibility of neural control. Fetz showed that neurons with consistent relationships to specific muscles could be operantly dissociated: a cell that always co-activated with the biceps could be driven to fire without any muscle activity, and vice versa. He interprets this not as rewiring of anatomical connections but as the brain exploiting its existing circuitry in variable patterns, analogous to trains taking different routes over fixed railroad tracks. This distinction between structure and activation patterns has profound implications for understanding how the brain achieves flexible behavior without constantly modifying its physical connectivity.

The Neurochip technology, developed with Andy Jackson and Jaideep Mavoori, enabled a breakthrough: autonomous, battery-powered devices mounted on the monkey's skull could record neural activity and deliver spike-triggered stimulation during days of free behavior. This allowed the creation of artificial recurrent connections between cortical sites, between cortex and spinal cord, and between cortex and muscles. In one paradigm, monkeys with temporarily paralyzed wrist muscles learned to drive a cursor into targets by activating motor cortex cells that directly stimulated the denervated muscles through the Neurochip.

The episode explores the relationship between volitional control and mental imagery, the challenges of reverse recruitment order when electrically stimulating muscles, and the potential for bidirectional brain-computer interfaces to restore function after spinal cord injury. Fetz draws a provocative parallel between the self's relationship to the brain and the brain's relationship to external devices, suggesting that the same mechanisms of flexible volitional control apply in both domains.