Brief light as a practical aversive stimulus for the albino rat

Abstract

Bright light was an effective aversive stimulus for Wistar rats in punishment, escape, and avoidance paradigms. Contingent punishment of lever pressing maintained by concurrent schedules of food delivery shifted presses to an alternate lever, and depressed overall response rates. Periodic non-contingent presentation of the light prompted escape responding (head entry into a hole). Unsignaled avoidance contingencies were not effective, but pre-pulse signaling of light supported avoidance behavior. These results demonstrate a possible alternative to foot-shock, one with greater ecological validity, and one that might avoid some of the physiological effects that accompany electric shock.

Figure 1

Mean (±SEM) proportion of presses on the lever that was preferred during baseline. The dashed line indicates indifference between levers. Baseline shows the initial proportion of presses on the preferred lever. When bright light was added on a VI 60 schedule, the proportion of responding shifted towards the originally non-preferred lever. When the rate of bright light presentation was increased to a VI 30 schedule a slight further decrease in preference was observed. When the bright light was Reversed onto the originally non-preferred lever, the proportion of responses on the preferred lever again increased. These data show that lever presses were less frequent on the lever that produced light. Results from the Mixed ANOVA are presented in the Experiment 1 results section.

Figure 2

A diagram of the experimental chamber used in experiments 2 and 3. The operant burrow apparatus, located in the front lower left quadrant of the chamber measures 60 mm deep and 50 mm in diameter, and contains an infrared photo beam at 21 mm for measuring head-entries.

Figure 3

Mean (±SEM) proportion of trials in which escape responses were emitted. Escape contingencies are described in parentheses using the format RL:LL:D, where RL is the Response-Light interval, LL is the Light-Light interval, and D is the duration of the light. The three baseline [(20:5:10), (20:5:5) and (20:5:5)] conditions were intermittently followed by conditions in which no light (0:0:0) was presented, bright light was made inescapable (0:5:5) and in which the Sidman avoidance contingency was debased (5:5:5). Results from the Mixed ANOVA are presented in the Experiment 2 results section.

Figure 4

Mean (±SEM) escape rate (head entries during the light) across 5 experimental conditions. Filled and empty symbols help identify experimental conditions. In the Escape Only condition, responses during the light terminated the stimulus and produced a 15 s dark period. The addition of an avoidance contingency during the Unsignaled Avoidance + Escape condition allowed subjects to delay the light onset for 20 s by producing a head entry prior to light onset. A tone was added 5 s prior to the light onset during the Signaled Avoidance + Escape condition. A regular increase in response probability was observed across the Escape Only, and Unsignaled and Signaled Avoidance + Escape conditions. Using a pulse of bright light to signal the avoidance period during the Pre-pulse condition reduced escape probability. Removal of the escape contingency during the Avoidance Only condition quickly reduced head entries during the light to near zero levels. Results from the Mixed ANOVA are presented in the Experiment 3 results section.

Figure 5

Mean (±SEM) avoidance response rate (head entries in the dark) across 7 experimental conditions. Filled and empty symbols are used to facilitate identification of experimental conditions. During the Escape Only condition responses in the dark were measured, but had no programmed effect. The addition of either an Unsignaled or Signaled Avoidance + Escape contingency produced no effect on avoidance responses. Using a pulse of bright light (Pre-pulse) to signal a 5 s avoidance period before light onset increased rates of avoidance responding. The removal of the escape contingency (Avoidance Only) further increased rates of avoidance. Reducing the duration of the aversive stimulus to match that of the pre-pulse cue (Brief) caused a slight decrease in avoidance responses. Removal of the pre-pulse cue while maintaining the shortened duration of the aversive stimulus further reduced responding. Results from the Mixed ANOVA are presented in the Experiment 3 results section.