Photographic Elimination of Transients (PET)

Abstract

Bioelectronic recording techniques have became a fundamental research tool in basic and applied neurophysiology and psychology.

Although the refinement of electronic apparatus has enabled bioelectrical measurement and recording to be made with great precision, the presence of noise or random discharges from the biological preparation itself may severely mask the desired potential changes and preclude waveform analysis. One solution to the problem of signal detection in noise utilizes mechanical devices or digital computers which superimpose and average a large number of electrophysiological records. Since the expectation of a random event is zero, algebraic methods reduce irregular background noise by a factor proportional to the square root of the number of observations (1). However, the cost of such computers is generally high and this precludes many laboratories from conducting detailed analyses of small signal evoked potentials. The purpose of this report is to present a simple photooscilloscopic technique of signal detection which is insensitive to the effects of large random transients. This technique may be utilized in present neurophysiological laboratories without modification of available equipment.

The components of the Photographic Elimination of Transients (PET) system are an oscilloscope and an integrated camera to photograph the beam tube face. A tape recording/playback system may be used in conjunction with this technique, or PET may be used directly from biological potentials. The PET procedure employs the multiple-sweep method by which a composite photograph is made of a number of similar superimposed waveforms from an oscilloscope display. Waveform alignment is obtained by triggering the oscilloscope sweep by an electrical pulse coincident with the stimulus presentation. However, PET differs from traditional sweep methods in that the intensity of the oscilloscope flying spot is reduced to the point where one full sweep does not appreciably expose the emulsion.