Aggression as positive reinforcement in mice under various ratio- and time-based reinforcement schedules

Abstract

There is evidence suggesting aggression may be a positive reinforcer in many species. However, only a few studies have examined the characteristics of aggression as a positive reinforcer in mice. Four types of reinforcement schedules were examined in the current experiment using male Swiss CFW albino mice in a resident-intruder model of aggression as a positive reinforcer. A nose poke response on an operant conditioning panel was reinforced under fixed-ratio (FR 8), fixed-interval (FI 5-min), progressive ratio (PR 2), or differential reinforcement of low rate behavior reinforcement schedules (DRL 40-s and DRL 80-s). In the FR conditions, nose pokes were maintained by aggression and extinguished when the aggression contingency was removed. There were long postreinforcement pauses followed by bursts of responses with short interresponse times (IRTs). In the FI conditions, nose pokes were maintained by aggression, occurred more frequently as the interval elapsed, and extinguished when the contingency was removed. In the PR conditions, nose pokes were maintained by aggression, postreinforcement pauses increased as the ratio requirement increased, and responding was extinguished when the aggression contingency was removed. In the DRL conditions, the nose poke rate decreased, while the proportional distributions of IRTs and postreinforcement pauses shifted toward longer durations as the DRL interval increased. However, most responses occurred before the minimum IRT interval elapsed, suggesting weak temporal control of behavior. Overall, the findings suggest aggression can be a positive reinforcer for nose poke responses in mice on ratio- and time-based reinforcement schedules.

Keywords: CFW mice; aggression; differential reinforcement of low rate; fixed-interval; fixed-ratio; nose poke; positive reinforcement; progressive-ratio.

Fig. 1

The frequency of nose pokes per min over the last five sessions for the 3 mice on the FR 8 reinforcement schedule. Baseline and extinction conditions are separated by dashed phase lines.

Fig. 2

Average interresponse times (IRTs) per session over the last five sessions in 1.0-s time bins on the FR 8 reinforcement schedule. IRTs greater than 20 s were incorporated into the 20-s bin. Black circles represent the first baseline condition and open circles represent the second baseline condition.

Fig. 3

Total postreinforcement pauses (PRPs) from the last five sessions in 30-s time bins for the 3 mice on the FR reinforcement schedule. Black circles represent the first baseline condition and open circles represent the second baseline condition.

Fig. 4

The frequency of nose pokes per min over the last five sessions for the 3 mice on the FI 5-min reinforcement schedule. Baseline and extinction conditions are separated by dashed phase lines.

Fig. 5

The cumulative number of nose pokes per quarter of the 5-min interval and corresponding index of curvature (IC) for the 3 mice on the FI 5-min reinforcement schedule, averaged over the last five sessions. Black circles represent the first baseline condition and open circles represent the second baseline condition.

Fig. 6

The number of completed schedules per session over the last five sessions for the 3 mice on the PR 2 reinforcement schedule. Baseline and extinction conditions are separated by dashed phase lines.

Fig. 7

The average PRP durations per session in seconds over the last five sessions for the 3 mice on the PR reinforcement schedule. Black circles represent the first baseline condition and open circles represent the second baseline condition.

Fig. 8

The rate of nose pokes per min over the last five sessions for the 2 mice on the DRL 40-s and DRL 80-s reinforcement schedules.

Fig. 9

The proportion of IRTs in 5-s time bins over the last five sessions for the 2 mice on the DRL reinforcement schedules. The first DRL 40-s condition is represented by black circles. The DRL 80-s condition is represented by grey triangles. The second DRL 40-s condition is represented by open circles.

Fig. 10

The proportion of PRPs in 10-s time bins over the last five sessions for the 2 mice on the DRL reinforcement schedules. The first DRL 40-s condition is represented by black circles. The DRL 80-s condition is represented by grey triangles. The second DRL 40-s condition is represented by open circles.