D. Chris Anderson

Physiological and behavioral effects of prior aversive stimulation (preshock) in the rat

Abstract Physiological and behavioral measures were assessed in rats that had been previously exposed to unsignaled inescapable intense shock (preshock). Animals subjected to such prior aversive stimulation exhibited greater adrenocortical steroid response compared to nonpreshocked controls when subsequently tested in the open field. An increment in defecation was also observed, with ambulation and rearing behavior being markedly inhibited in the preshocked rat during these sessions.

Alteration in footshock threshold by low-level septal brain stimulation☆

Abstract Thirteen male, hooded rats with chronically implanted electrodes in the septal area were trained to bar press for intracranial stimulation (SICS) to determine whether the electrode locus was in a reward zone, and then were tested for footshock threshold in a highly-sensitive startle chamber in the presence and absence of SICS on randomly alternated days. SICS (a) significantly decreased startle responses to all footshock levels, (b) decreased magnitude of startle to footshock, and (c) was least effective in altering footshock threshold when the electrode locus was in a reward zone. Effects (a) and (b) were most prominent in initial test periods, but diminished over subsequent sessions.

Preconditioning CS exposure: Variation in place of conditioning and of presentation

Two groups of rats were given preconditioning CS (PCS) exposures in an operant box after learning to bar press for food. One-half of two other groups were given similar PCS exposures in a holding cage, but otherwise were treated identically. One group that got PCS in the operant box and one that did not were given 10 CS-US (buzzer-shock) pairings in the operant chamber while the other two were identically conditioned in a cylindrical chamber. A fifth group got only the US. CS presentations following conditioning produced the most suppression of bar pressing for Ss that got no PCS, intermediate suppression if the PCS was given in the holding cage, and no suppression if preexposures occurred in the operant chamber. These effects were independent of place of conditioning.

Dual effects of a second-order conditioned stimulus: Excitation and inhibition

On alternate days during Sidman avoidance training, four groups of four Ss each were conditioned in a separate chamber. Group 1 received 10 forward first-order (CS1-US) and 20 forward second-order (CS2-CS1) conditioning trials until 100 of the former and 200 of the latter were completed. For Group 2 second-order trials involved a random contingency. Only the CS1 was presented Group 3 on the first 180 of the 200 second-order trials. Group 4 was like Group 3 except that the last 20 CS2-CS1 trials involved a random contingency. During extinction of the avoidance response onset of CS1 occasioned accelerated response rates for all groups. CS1 offset produced below-baseline response depression. The CS2 accelerated responding for Group 3, depressed performance for Group 1, and left basically unchanged Groups 2 and 4.

Preshock-produced intensification of passive avoidance responding and of elevation in corticosteroid level

Abstract The adrenocortical steroid response and passive avoidance behavior were studied in rats that had been exposed to inescapable intense shock (preshock). Previously preshocked animals exhibited a greater adrenocortical steroid response to mild shock than nonpreshocked controls; in addition, passive avoidance behavior was facilitated in the preshocked animals.

Second-order fear conditioning as revealed through augmentation of a startle response: Part II

A loud, abrupt auditory startle stimulus was presented 1, 17, and 27 sec following termination of a classically conditioned, fear-evoking, second-order stimulus. Forward, second-order conditioned Ss consistently exceeded the startle magnitudes of backward, second-order conditioned controls at all intervals with one exception (the 1-sec interval).

Preconditioning exposures to the CS: Variation in place of testing

One of three groups (Group 1) was given nine 30-sec preconditioning CS (PCS) exposures while bar pressing for food. Half of the remaining groups got the PCS treatment in holding cages. Group 1 and Group 2 then received 12 CS-US pairings elsewhere. Group 3 was given the US only. Group 2 suppressed bar pressing to the CS during testing more than Groups 1 (p <.02) or 3 (p <.01) although the PCS-treated half of Group 2 was somewhat less suppressed than the non-PCS half. Group 1 showed more suppression than the other two when all subsequently were tested for running to the CS in an alleyway.

Influence of duration and number of inescapable shocks on intrashock activity and subsequent interference effects

A three-phase investigation of the effects of duration and number of inescapable shocks with rats was conducted. In the first phase (shock treatment), separate groups were exposed either to 64 or 128 5-sec shocks or to 32, 64, or 128 10-sec shocks. Measures of intrashock activity were found to be lower for the groups exposed to 64 or 128 10-sec shocks than for any other group. In the second phase (Test Day 1), half of each group was tested for interference with FR 1, locomotor escape-avoidance learning at either 24 or 168 h following cessation of shock treatment, using a control procedure that was designed to equate groups for exposure to test shock. The results indicated that, relative to nonshock-treated controls, at each interval only the groups previously given 64 or 128 10-sec shocks were impaired in terms of escape frequency. However, all groups given at least 64 shocks exhibited depressed intertrial responding at the 24-h, but not the 168-h, interval. In the final phase (Test Days 2–4), the control procedure for equalizing test-shock exposure was discontinued and a pattern of interference effects was observed in terms of escape-avoidance response latency that was identical to that reported for the escape frequency in Phase 2. In general, these data were viewed as indicating that duration, but not total amount of shock, was a critical determinant of behavior during inescapable shock and of the subsequent interference effect. Both effects of duration were regarded as the product of a common associative process involving the learning of immobility tendencies to shock that served to compete with later escape-avoidance responding.

Effects of a Contextual Change upon Retroactive Inhibition

It was predicted that retroactive inhibition could be produced using meaningful passages of prose. In addition, it was hypothesized that if the interpolated session took place in a context which was markedly different from the room used during original learning, the amount of retroactive inhibition would be less. Also, if there was a contextual change between the original learning and the recall session, retention would be less. A passage describing Jim as an extravert was first presented, followed by one describing him as an introvert. A classroom and cafeteria served as contrasting contexts. The hypotheses were confirmed.

Shuttle interference effects in the rat depend upon activity during prior shock: A replication

An omission-training procedure involving a passive-escape contingency was used to reduce the amount of movement during shock exhibited by rats below that of yoked controls exposed to a physically identical but inescapable shock. Subsequent tests for interference with two-way, FR 1 escape/avoidance learning revealed only the passive-escape subjects to be impaired relative to previously restrained but nonshocked controls. These findings duplicated the results of an experiment by Anderson et al. and were viewed as indicating that behavior during shock, rather than uncontrollability, is the critical determinant of proactive shock treatment effects.