Effects of Scopolamine on Conditioning of Lever Pressing

The aim of this work was to determine the effects of scopolamine, a cholinergic antagonist, on the conditioning of an instrumental response and the contextual conditioning of this response. Five groups of rats were trained to lever-press on a Variable Interval 30 s schedule in context A. Scopolamine was administered 15 min before each conditioning session to AB 0.01 mg/kg, AB 0.10 mg/kg and AB 1.00 mg/kg groups. The AA Saline and AB Saline groups received saline injections.Contextual conditioning of the lever-pressing response was assessed in one extinction session. The AA group received this extinction session in the conditioning context (A), while the AB groups received this session in a different context (B). Results showed that scopolamine impaired the conditioning of the lever-pressing response but no effects on contextual conditioning were found.

A SYSTEMATIC REPLICATION OF SKINNER (1938) USING A HOT AIR BLAST AS THE PUNISHER

The present study was a systematic replication of the classic study by Skinner (1938) using a hot air blast (HAB) as the punisher. After lever press training, six rats underwent two extinction sessions. During the initial 10 min of extinction in the first session, half of the subjects received a HAB for every lever press (punishment). Subjects that received punishment made fewer lever presses during first extinction session, but the total number of responses in both groups was equivalent by the end of the second extinction session. The present data corroborate the findings of Skinner (1938) that the punishment may have partial and temporary effects in certain contexts. We discuss the ways in which the elicitation of competitive responses, the intensity and nature of the stimulus, and the duration of exposure to the aversive contingency are important factors that may explain the divergent results in the literature.Keywords: punishment, replication, competitive responses, suppression, rats, hot air blast

Post-extinction Delay Necessary to Induce Retrograde Amnesia for a Moderate Extinction Training Memory

Two experiments using rats were conducted to evaluate the post-extinction delay necessary to obtain retrograde amnesia for a moderate extinction training memory. In Experiment 1, six minutes of extinction (i.e., cue-exposure) was sufficient to reduce fear of the black compartment of a white-black shuttle box, however the amnestic treatment cycloheximide (CHX) failed to produce retrograde amnesia for extinction (i.e., show fear). In Experiment 2, CHX was administered at various post-extinction delays (0-min, 60-min, 75-min, 120-min) to assess whether the active extinction memory could be susceptible to amnesia if the original fear memory had time to reconsolidate. The results indicated that administrating CHX 75 minutes after extinction produced retrograde amnesia for extinction, but not for shorter post-extinction delays, thus demonstrating a temporal gradient. These findings suggest that the extinction memory was active and susceptible to disruption 75 minutes after the extinction session, but the original fear memory may have been protected from the amnestic effects with sufficient time to reconsolidate.

Contrasting ABA, AAB and ABC Renewal in a Free Operant Procedure

One experiment used a free operant procedure with rats to compare ABA, AAB and ABC renewal by using a within-subject testing procedure. All rats were first trained to press a lever for food in context A. Lever pressing was then extinguished in either context A or context B. For rats in the groups ABA and ABC extinction took place in context B, while the rats in group AAB received extinction in the same context in which acquisition took place (context A). Finally, all rats were tested for renewal in two sessions. One extinction session was carried out in the same extinction context and another session in a different context. Rats in the group ABA were tested in context B and in context A; rats in the group AAB were tested in contexts A and B, whereas the group ABC was tested in contexts B and C. The results of the ANOVA showed context renewal since all groups had higher rates of responding when they were tested outside the extinction context, F(2, 21) = 15.32, p = .001, ηp2 = .59; however, AAB and ABC renewal was lesser than ABA renewal, F(1, 21) = 16.70, p = .0001, ηp2 = .61.

Effect of Effort and Latent Extinction on Resistance to Extinction

Sixty-four male Wistar rats were given acquisition training in an enclosed straight-alley runway which could be adjusted for angles of inclination. The 2×2×2 design involved two angles of inclination in acquisition (0° and 40°) and two angles of inclination in extinction (0° and 40°). Between acquisition and extinction, half the subjects were exposed to a latent extinction procedure and half served as controls. Number of responses in a 30-min extinction session was an inverse function of effort required in extinction. Additionally, latent extinction procedures resulted in reduced resistance to extinction, but only when the effort conditions of acquisition and extinction were constant. When the effort conditions of acquisition and extinction were dissimilar, latent extinction procedures resulted in increased resistance to extinction. The results raise questions about the nature of the learning which occurs during latent extinction training.

Successive Acquisitions and Extinctions with Goldfish (Carassius Auratus) in a Swimway Situation

Goldfish were trained in a successive acquisition and extinction shuttle-swimway situation. Groups of 12 fish experienced alternating days of acquisition and extinction, extinction following immediately after each daily acquisition session, and acquisition following immediately after each daily extinction session. None of the groups produced decreasing resistance to extinction across extinctions within eight successive acquisitions and extinctions. A group of fish given 16 successive acquisitions and extinctions with alternating days of acquisition and extinction learned to decrease swimming speeds after eight successive extinctions. However, these fish also decreased acquisition speeds across the last 8 successive acquisitions.

Effects of Chlorpromazine and Pentobarbital on Pattern and Number of Responses in Extinction

In a series of experiments rats were trained and subsequently extinguished under different conditions of drug administration. High doses of chlorpromazine (5 mg/kg) or pentobarbital (20 mg/kg) were administered during the first extinction session and the dose was progressively reduced to zero over 10 successive sessions. Extinction was continued until all Ss had consistent near zero responding. When compared to saline control, chlorpromazine had no effect on total extinction responding, while pentobarbital significantly reduced total extinction responding. Ss receiving both drugs had erratic runs of responding in extinction, whereas Ss receiving saline showed a normal extinction pattern. Ss receiving pentobarbital during both training and extinction had more total extinction responding than Ss receiving only pentobarbital in extinction.

Repeated Acquisition and Extinction of Barpressing in Rats and Guinea Pigs

On each of 10 days rats and guinea pigs first barpressed for 15 reinforcements on a CRF schedule and then were immediately extinguished during an unsignalled 10-min. extinction session. Analysis of the number of bar-presses during each of 10 extinction sessions indicated a significant reduction for rats but not for guinea pigs because the level of barpressing remained consistently high immediately following reinforcement for the guinea pigs but declined progressively faster within successive extinction sessions for rats. Results support the idea that organisms with well developed sensory-motor capacities at birth are less able to inhibit previously rewarded responses than those with slower development.