Responses of worms to light as a function of intertrial interval and ganglion removal.

Abstract

Unconditioned responses of earthworms, Lumbricus terrestris, to light were found to be a complex function of time between test trials and ablation of supra and subpharyngeal ganglia. Normal worms made more. URs to light with an 88-sec. ITI than with a 6-sec. ITI; more than 90% of URs were withdrawal (negative) responses; adaptation as measured by increased latencies occurred across 60 test trials. Ablation of supra, sub, or both neural ganglia led to decreased URs only for worms tested with 88-sec. ITI; more than 50% of URs were approach (positive) responses. Results are related to effects of ITI on conditioning and theory of ganglion control of response to light.

The effect of the anterior ganglia on forward movements in the earthworm

“…After assignment, each S was rinsed in distilled water, and Ss in the experimental group had the anterior five segments removed according to the surgical procedure described by Ratner and Stein (1965). The Ss in the control group were similarly handled, but no surgery was performed.…”

Differentiating ganglionic function in the earthworm.

“…Interpretations differing from this view have been put forward (e.g., Blue, 1976). Traditionally, a large number of investigations depended on evaluations of the earthworm's response to light stimuli (e.g., Blue, 1976;Hess, 1924;Howell, 1939;Janzen, 1931;Mast, 1911;Mendelson, 1978;Nomura, 1926;Peeke, Herz, & Wyers, 1965;Prosser, 1934b;Ratner & Miller, 1959;Ratner & Stein, 1965;Ward & Doolittle, 1973), and neither the nature of the animal's response to light nor the specific points of difference between supra-and subpharyngeal roles in that response are always clear (see Doolittle, 1971;Hess, 1924;Mast, 1911;Nomura, 1926;Smith, 1902). Further, qualification of results has proved necessary: The form or direction of a behavior may change during recovery from the ablation (Prosser, 1934a;Ward & Doolittle, 1973); with repeated trials (Mendelson, 1978;Nomura, 1926); and with excessive manipulation of the animals Copyright 1979 by the American Psychological Association, Inc. 0021-9940/79/9306-1136$00.75 (Howell, 1939).…”

Chemistry of Learning

“…All of the studies of classical conditioning with L. terrestris (see above) include groups of worms that receive repeated stimulation using only one of the stimuli that are paired for the conditioned groups. Ratner and Stein (1965) also studied habituation to photic stimulation with L. terrestris and studied habituation, over habituation, and retention of habituation of withdrawal responses to mechanical, vibratory stimulation.…”

“…The validity of this preparation is suggested by findings on the effect of variables such as intertrial interval (Ratner and Stein, 1965), stimulus intensity (Morgan, Ratner, and Denny, 1965), and retention intervals . Short intertrial intervals reduce frequency of responses; intensity of a photic stimulus has a positive relation both to the initial level of responding and to the rate of habituation; and retention of a habituated response proceeds in the manner of the classic remembering curve found with other species.…”