Introduction to motor prosthetics

Fritsch and Hitzig first discovered the motor cortex in 1870 [1], although the best-known experimental mapping of the motor cortex dates back to Penfield’s experiments in 1937 [2] using electrical stimulation to activate muscle groups in patients undergoing surgery for epilepsy. It was not until the 1980s, over 100 years since the discovery of the motor cortex, that population coding [3] was proposed and thus the beginnings of decoding neural signals in the motor cortex into their corresponding motor function.

In 1998 the first human was implanted with a brain–machine interface (BMI) of high enough quality to simulate movement and demonstrated two-dimensional control of a mouse cursor [4],[5]. Since then, there has been an explosion of demonstrations of motor prosthetic control of computer cursors and robotic arms by both primates and humans. In the last year, the same group demonstrated robotic arm control with four degrees of freedom in a tetraplegic patient [6]. These demonstrations mark a significant step in bringing BMIs from the research arena to viable medical devices, but a number of technological hurdles must still be overcome to make this a reality.

A simplified diagram of a BMI system is exemplified in Figure 29.1. A full BMI system involves a recording device to take signals directly from the motor cortex.