The caudal photoreceptor of the crayfish: quantitative study of responses to intensity, temporal and wavelength variables

Quantitative measurements of the multicellular activity recorded with gross electrodes from the ventral nerve cord of the crayfish have been made to determine the adaptation function, the spectral sensitivity and the relation between stimulus intensity and response amplitude of the simple photoreceptor located in the sixth caudal ganglion. A digital computer analysis technique was used to discriminate between those fibers associated with the photic stimulation and other spontaneously active neurons and to perform the bookkeeping operations of peak detection, and tabular and graphic display of amplitude and interval distributions. The neural output was found to adapt considerably over a period of one minute with high activity rates (produced by high level stimuli) showing a greater percentage decrease in activity than lower rates. A constant energy spectrum was produced by means of a grating monochrometer and the luminosity function plotted by measuring the total amount of activity in a two second sample. The photosensitivity function was found to closely approximate the luminosity curve of the dark adapted human eye. The relation between stimulus intensity and response amplitude was found to be well fitted by a power function with an exponent of 53.