Peak discrimination as a method for quantitative evaluation of neural activity by computer

A computer method (PDP-12) for the quantification of neural activity in single- as well as few-fibre preparations of nerves was devised and tested on function-generator signals and on neurograms from baro- and chemoreceptor fibres of the carotid sinus nerve of rabbits. The principle of the program was to search continuously for maxima and minima of the electrogram regardless of the absolute voltage range in which they occurred. Action potentials were then distinguished from noise by comparing these maxima with amplitude discriminators. The latter were derived from the previous analysis of noise in selected neurograms and in recordings during activity-free intervals of the normal electrogram or temporary cold block of the preparation. From peaks accepted as action potentials the program computed total mean frequency, amplitude histogram and interval histogram as standard outputs. The method permitted one to determine in few-fibre preparations not only total activity but also response characteristics of different fibre components. However, owing to principal limitations shown to be inherent in such techniques, the exact quantification of neurograms from several fibres became impossible if the mean frequency—depending on the type of activity—exceeded several hundred to about 1000 impulses/s. By systematic variation of program parameters and type and rate of neural activity, the performance characteristics of the program as well as certain general properties of single-, few- and multi-fibre neurograms were evaluated.