A computerized discriminator for action potentials.
A system for recognizing extracellular action potentials in the presence of noise and other pulses was developed for a PDP11/23 computer. Data can be processed either on-line or off-line from a tape recorder. There are 4 parts: (1) An RC bandpass filter attenuates noise. (2) The data input program digitizes the signal every 55 mu sec. If the signal exceeds a threshold, 12 samples of the signal and the time are written onto the disk. Up to 300 pulses/sec can be processed. (3) The pulse discriminating program recognizes an action potential by fitting the 12 points with this function: v(t) = (a + bt + ct2) exp(-t/tau). It is biphasic, has two zeroes, and decays to zero at long times. There are 4 parameters, a, b, c and tau. The operator chooses a value of tau giving good fits for all pulses of this neuron. For each pulse the computer determines values of a, b and c by the least squares technique. The zeroes of v(t) are computed. For acceptance, the total pulse height (difference between extreme voltages), the position of the first zero, and the time between zeroes must be within limits. The 12 points and v(t) can be displayed. Summary statistics and histograms are printed. It takes 80 msec/pulse for these off-line computations. (4) Occasionally a pulse may be missed or an extra one recorded. The pulse insertion-deletion program edits the disk files. The instantaneous-interspike-frequency plot is displayed and the operator moves cursors to insert or delete pulses.
D000200:Action Potentials; D003201:Computers; D004569:Electroencephalography