Single neuron recording from motor cortex as a possible source of signals for control of external devices

Abstract

For the severely handicapped patient, such as a quadriplegic, a large number of independent signals would be desirable to control neuromuscular stimulators that could impart movement to the paralyzed limbs. We have investigated the possibility of making long-term connections to the central nervous system with microelectrodes. Monkeys have been implanted with arrays of intracortical electrodes for periods of up to 37 months, indicating that long-term connections to the nervous system are possible. A second question investigated was whether the implanted monkeys could learn to modify the firing patterns of recorded neurons to control a device outside of their bodies. Through the use of an 8 target tracking task a monkey was able to produce an information transfer rate of 2.45 bits/sec when cortical cell signals were the monkey's output. The same task was performed having the monkey move a handle by wrist flexion and extension (i.e., using the intact motor system as the output). The information transfer rate increased to 4.48 bits/sec, or less than a twofold improvement. Thus, the direct output of cortical cells can provide information transfer only moderately less precise than the intact motor system. Our preliminary studies have been encouraging on obtaining connections to the nervous system to control external devices. However, numerous improvements are required in electrode design, fabrication, implantation, and signal processing techniques before this method of obtaining control signals would be feasible for human applications.