Stable long-term recordings from cat peripheral nerves.

A procedure has been developed for the stable long-term recording of nerve signals in unanesthetized mammals, which should have wide application in basic research on the nervous system and also in clinical areas such as the derivation of control signals for powered prostheses. Methods are fully described for constructing devices consisting of (1) Silastic nerve cuffs containing three or more electrodes, (2) coiled leads insulated with Silastic which extend from the cuffs to an integrated circuit socket, (3) a vitreous carbon transcutaneous connector which surrounds the integrated circuit socket and makes a good interface with the skin. Neural activity has been recorded from mammalian nerves for many months during normal behaviour. The peak-to-peak amplitude and latency of the recorded compound action potentials remain stable and may continue at a constant level more or less indefinitely. A tripolar recording configuration between a central lead and the two end leads, which are connected together, permits good rejection of EMG signals from surrounding muscles. The amplitude of single unit potentials increases as the square of the conduction velocity of the nerve fibre. Thus, the largest nerve fibres will dominate the signals recorded during behaviour. The reasons for premature termination of a few experiments are given together with methods for overcoming these problems. For example, platinum-iridium electrodes remain relatively stable, whereas silver wires tend to fracture after being in an animal for several months. This and other relationships are discussed which permit an optimal design of nerve cuffs for a given recording situation.