Immediate post-reminder injection of gamma-amino butyric acid (GABA) agonist midazolam attenuates reactivation of forgotten fear in the infant rat.

J. H. Kim, G. McNally, and R. Richardson (2006) reported that pretest injection of FG7142, a GABA inverse agonist, alleviated infantile amnesia in rats. From this, it was concluded that GABAergic neurotransmission is involved in the forgetting seen in the developing rat. The present study extends that finding by examining the role of GABA in the reactivation of a forgotten memory in the infant rat. Sixteen-day-old rats were conditioned to fear a white noise. When tested 3 days later, rats that had not received a reminder treatment exhibited substantial forgetting. Reactivation of memory (as assessed by high levels of freezing) was observed in rats that were given a reminder shock and injected with saline the day before test. However, rats given a reminder shock and injected with midazolam immediately afterward failed to exhibit the reactivation effect. A subsequent experiment replicated this finding and further showed that midazolam did not reduce the memory reactivation effect when injected 2 hr after the reminder episode. From this, it appears that alterations in GABAergic neurotransmission may be an underlying process mediating memory reactivation in the infant rat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogenetic differences in the expression of conditioned stimulus conditioning: effects of retention interval

Preweanling 17-day-old rats were tested for retention of the conditioned emotional response after a 5-min or 24-hr retention interval. For a variety of conditioning parameters (i.e., variation in conditioned stimulus modality, unconditioned stimulus intensity, number of training trials), conditioned responding was consistently weaker after 5 min than after 24 hr. This apparent "incubation," or "hypermnesic," effect was not found in adult rats, even when comparable conditioning levels were indicated on the 24-hr test. The transient short-term retention deficit observed in 17-day-old preweanlings was alleviated by placing the pup in its home cage during the 5-min retention interval or by extending the conditioning session. Fifteen-day-old rat pups did not benefit from home cage exposure or extended training and displayed the transient short-term retention deficit regardless. The results are discussed in terms of age-related effects on time-dependent memory consolidation.     

Isolation disrupts retention in preweanling rat pups.

Expression of an olfactory memory in 18-day-old rat pups was examined in eight experiments following brief manipulations of environmental conditions prior to a retention test. In the first experiment we found that retention was disrupted if a pup was placed in isolation for 3 hr prior to the retention test. The retention deficit persisted even when pups had 3-hr exposure to an anesthetized dam and siblings before testing. However, there was no deficit in retention if pups spent the pretest interval with a nonlactating foster dam, their father, or littermates. Finally, we found that this deficit in retention could be alleviated by cuing treatments that preceded the retention test following isolation. Both discrete cues used during training and returning the pup to the home cage with parents and siblings for 3 hr were found to alleviate the retention deficit caused by isolation. These data demonstrate that housing conditions can influence postacquisition memory processes in the young animal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparative learning and memory deficits following hippocampal and caudate lesions in mice.

Examined the effects of hippocampal, caudate, combined hippocampal-caudate, and sham lesions on the passive avoidance and active escape performances of groups of female CF1 mice. Bilateral hippocampal or caudate lesions produced similar impairments of passive-avoidance retention 1 day after training in Ss operated upon 1 day prior to training. Hippocampal and caudate lesions similarly facilitated active-escape retention. When surgery was performed immediately after training, hippocampal or caudate lesions each impaired both passive-avoidance and active-escape retention 1 day later; no retention deficits were observed when surgery was performed 1 hr. after training. When surgery was performed immediately after training and passive-avoidance retest was conducted 1 hr. later, only hippocampal lesions impaired retention. These and other data suggest the mediation of different neuroanatomical substrates for short- and long-term memory and different processes for storage and forgetting. (19 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A comparison of contextual and generalized auditory-cue fear conditioning: evidence for similar memory processes

A number of variables influence contextual, but not auditory-cue, fear conditioning. However, several of these variables (isolation, stimulus preexposure, retention interval, and age) affect generalized auditory-cue fear. More generalized fear was found when (a) rats were isolated in a novel environment than when returned to their home cages, (b) the retention interval was 3 hr rather than 24 hr, and (c) in 18-day-old compared with 25-day-old rats. Moreover, preexposure to the auditory cue eliminated the isolation effect. At a behavioral-psychological level, these variables may exert their effects by influencing the processes that construct a memory representation of the stimulus. At a neural systems level, they may influence processing carried out in the thalamo-corticoamygdaloid auditory pathway.     

Rate of acquisition, adult age, and basic cognitive abilities predict forgetting: New views on a classic problem.

Rate of forgetting is putatively invariant across individuals, sharing few associations with individual-differences variables known to influence encoding and retrieval. This classic topic in learning and memory was revisited using a novel statistical application, multilevel modeling, to examine whether (a) slopes of forgetting varied across individuals and (b) observed individual differences in forgetting shared systematic relations with adult age, learning speed, and cognitive ability. Participants (N = 136) received mnemonic training prior to memorizing 4-digit numbers to perfection, and retention was tested immediately after training and after 30 min, 24 hr, 7 weeks, and 8 months. Slower rate of learning to criterion, older age, and poorer cognitive performance predicted accelerated forgetting with associations most pronounced within 24 hr from baseline. Observed correlates of differential forgetting slopes are similar to those previously found to affect encoding, suggesting continuity rather than asymmetry of prediction for these memory processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Alleviated forgetting of a learned contingency in 8-week-old infants.

To investigate retention by 8-wk-old infants (N?=?24) after lengthy intervals, the authors first determined that infants of this age reliably learned an operant contingency in 2 training sessions and evidenced no retention of it 14 days later (Exp I). To determine whether the memory of the contingency was permanently inaccessible or whether forgetting could be alleviated by a prior cueing procedure known to facilitate retrieval in older infants, a "reactivation" treatment was administered 17 days after training was completed, and cued recall was examined 24 hrs later (Exp II). Control groups received either no reactivation treatment prior to the retention test or a reactivation treatment but no prior training. Experimental Ss showed little or no forgetting, but Ss in the 2 control groups responded at their pretraining baseline rates during the long-term retention test. These data challenge the general assumption of deficits in memory processing by 8-wk-olds and demonstrate that memories acquired either prior to or during a period of major neurological and behavioral reorganization can be maintained through that period. (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Combined effect of context change and retention interval on interference in causality judgments.

Four experiments studied the effects of context change and retention interval on retroactive interference in human causal learning. Experiment 1 found evidence of retroactive interference. Experiment 2 found that either a 48-hr retention interval or a change in the context after the interference treatment decreased retroactive interference. An interaction between context change and retention interval effects was also found, eclipsing the context change effect after the 48-hr retention interval. Experiments 3 and 4 found additivity between context change and retention interval effects when participants were reminded of the difference between physical contexts before the test, independently of whether the context change involved a return to the original acquisition context. These results add to the evidence suggesting that spontaneous forgetting is caused by a change in either the physical or the temporal contexts when information is acquired. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Postconditioning isolation disrupts contextual conditioning: an experimental analysis

Contextual-fear conditioning requires a lengthy retention period to fully emerge. This phenomenon might reflect the consolidation of a representation of the context that can be used to evoke fear. To investigate this hypothesis, 25 day-old rats that were returned to their home cages after conditioning were compared with rats that were isolated in a novel room. Isolation disrupted contextual but not auditory-cue fear conditioning when the conditioning-isolation interval was 2 hr or less, but not when it was 24 hr. Preexposure to the context prevented the isolation effect, and isolation disrupted this effect of context preexposure. These results support the consolidation hypothesis and the view that contextual- and auditory-cue fear conditioning depend on different processes.     

Acquisition and retention of a letter-detection skill.

In two experiments, we examined the acquisition and retention of a letter-detection skill with a consistent-mapping procedure. In Experiment 1, subjects were trained from 0 to 4 sessions at detecting the letter H in displays containing random letters, and retesting occurred after a 1-month delay. Performance improved and in some cases became more automatic, and the performance level was maintained over the retention interval. When tested with a prose passage, the high error rate on the word THE was eliminated after training and after the retention interval, regardless of the amount of training. In Experiment 2, two subjects were given 12 sessions of training followed by a retention test 6 months later. For 1 subject there was also a retention test 15 months after acquisition. Performance improved dramatically with training, and substantial but not complete automaticity was achieved. Performance on the retention tests was close to the final acquisition level. The surprising lack of forgetting in this study was contrasted with the substantial forgetting typically found in studies of verbal learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of intra-amygdaloid infusions of a D? dopamine receptor antagonist on Pavlovian fear conditioning.

The present study examined the effects of bilateral intra-amygdaloid infusions of the D? receptor antagonist, eticlopride, on the acquisition and expression of Pavlovian fear conditioning as measured by freezing to acoustic and background contextual stimuli in the rat. Infusions of eticlopride before acquisition or before both acquisition and retention testing significantly attenuated conditioned freezing to tone presentations during the retention test 24 hr later. No effects, however, were observed on freezing that emerged during acquisition. Furthermore, these effects were not attributable to state-dependent learning effects or alterations in baseline activity or shock reactivity. In conclusion, these results suggest that amygdaloid dopamine transmission at D? receptors contributes to the formation and/or consolidation of fear memories (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Forgetting the once-seen face: Estimating the strength of an eyewitness's memory representation.

The fidelity of an eyewitness's memory representation is an issue of paramount forensic concern. Psychological science has been unable to offer more than vague generalities concerning the relation of retention interval to memory trace strength for the once-seen face. A meta-analysis of 53 facial memory studies produced a highly reliable association (r=.18, d=0.37) between longer retention intervals and positive forgetting of once-seen faces, an effect equally strong for both face recognition and eyewitness identification studies. W. A. Wickelgren's (1974, 1975, 1977) theory of recognition memory provided statistically satisfactory fits to 11 different empirical forgetting functions. Applied to the results of field studies of eyewitness memory, the theory yields predictions relevant to fact finders' evaluations of eyewitness credibility. A plausible upper limit for witness initial memory strength corresponds to a probability of .67 of being correct on a fair six-person lineup. Furthermore, not only can the percentage of remaining memory strength be determined for any retention interval, but this strength estimate can be translated into an estimated probability of being correct on a fair lineup of a specified size. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Opioid receptors regulate retrieval of infant fear memories: Effects of naloxone on infantile amnesia.

The authors examined the role of the endogenous opioid system in infantile amnesia for contextual fear conditioning. Rats that were 18 days of age received an aversive footshock in a novel context. Rats displayed conditioned fear when tested 1 min after training but not 24 hr after training. Systemic injection of the opioid receptor antagonist naloxone prior to test, but not immediately after training, alleviated infantile amnesia. Naloxone also alleviated infantile amnesia when injected prior to test 7 days after training. These effects of naloxone were due to actions on central rather than peripheral opioid receptors and were not due to any tendency of the drug to produce fear or freezing. These results show that central opioid receptors regulate retrieval of fear memories in infant rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of intentional forgetting in reducing children's retroactive interference.

Preschool and kindergarten children's retention of stories was examined in the presence of interfering information and instructions to forget. Children learned 2 stories and, 24 hr later, were asked to recall the 1st or 2nd story learned. Some of the children were instructed, either following acquisition or just prior to the retention test to forget the 2nd, or interfering, story. A model was used to isolate storage and retrieval effects, and the results showed that (a) retroactive interference affected both storage- and retrieval-based forgetting rates for the younger children but only storage-based forgetting rates for the older children, (b) intentional forgetting reduced retroactive interference primarily by attenuating storage-based forgetting regardless of age, (c) intentional forgetting instructions were effective only at acquisition for preschoolers but at both acquisition and retention for kindergarteners, and (d) all children recalled the to-be-forgotten story as well as they recalled the to-be-remembered story. These results are interpreted in terms of reorganization and distinctiveness effects in storage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reactivation of a visual discrimination in early infancy.

16 78–92 day old infants learned to produce movement in 2 successively presented overhead crib mobiles by footkicking in a conjugate reinforcement paradigm. The mobiles differed in both color and pattern displays on the suspended components. Following acquisition, a discrimination was introduced whereby responding was reinforced in the presence of one mobile (the positive stimulus; S+) but not in the presence of the other (the negative stimulus; S–). During a cued-recall retention test administered 21 days after the completion of discrimination training, Ss evidenced no retention of either initial or discrimination training. Nevertheless, a brief reactivation treatment with S+ 24 hrs prior to the long-term retention test alleviated forgetting and restored the S+/S– discrimination. Reactivation with S– was no more effective than no reactivation treatment at all. Results confirm the efficacy of reminder procedures with young infants and demonstrate the specificity with which the reminder alleviates forgetting. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Expression of renewal is dependent on the extinction-test interval rather than the acquisition-extinction interval.

A recent finding suggested that when extinction occurs shortly after acquisition, renewal of an extinguished fear response (fear-potentiated startle) to a light conditioned stimulus (CS) is diminished (Myers, Ressler, & Davis, 2006). The present study attempted to extend this finding using a white-noise CS and freezing as the behavioral measure of fear. In Experiments 1A and 1B, we observed renewal whether extinction occurred 10 min or 24 hr after acquisition. In contrast, renewal was not observed if test occurred 10 min after extinction (Experiment 2). Experiment 3 demonstrated that expression of extinction at the 10-min extinction-test interval was attenuated by a pretest subcutaneous injection of the γ-aminobutyric acid (GABA) inverse agonist FG7142. These findings suggest that renewal is influenced more by the extinction-test interval than the acquisition-extinction interval. Further, the failure to see renewal 10 min after extinction suggests that there is a separate context memory that undergoes a different consolidation function than the CS-no US memory formed during extinction. Finally, the expression of extinction appears to be GABA dependent regardless of the extinction-test interval or the test context. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Directed forgetting in implicit and explicit memory tests: A comparison of methods.

Directed forgetting has been studied by instructing Ss to forget either (1) an initial list or (2) individually selected words. Differential encoding was hypothesized to be responsible for word-method directed forgetting, and retrieval inhibition for list-method directed forgetting. In Exps 1 and 2, directed forgetting was observed in recognition with the word method but not with the list method. Release from directed forgetting occurred in final recall after recognition but only with the list method. These results are interpreted in terms of a theoretical framework that integrates distinctive-relational processing theory with revised generation-recognition theory. In Exps 1–3, predictions from that framework were generally well supported on implicit and explicit retention tests that provided the same stimulus conditions. Consistent with processing theory, list-method directed forgetting was absent on data-driven or conceptually driven implicit tests, and word-method directed forgetting was absent on data-driven implicit tests. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adult age differences in forgetting sentences.

Carried out age comparisons of performance-based measures of forgetting. In Exp 1, 18–21 yr olds and 55–64 yr olds (n?=?24) forgot at an equal rate when compared at 30 sec and 3, 6, and 24 hrs after acquisition. In Exp 2, 17–21 yr olds and 65–74 yr olds (n?=?24) were compared at the same 4 retention intervals. Initial learning was equated for the 2 groups. There was evidence for an age difference in forgetting rate in cued recall when a minimal learning level was required. In Exp 3, 440 men and women (aged 17–74 yrs) were assigned to a retention interval from 10 min to 7 hrs. Age was related to 4 performance-based measures of forgetting rate. Although the age differences were small, they imply 2 decremental processes: one before 10 min, possibly a result of incomplete consolidation, and a later one that is continuously and cumulatively operative thereafter. Evidence relating initial level to forgetting rate is presented. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Trial distribution effects on postasymptotic performance and retention of the rabbit's (Oryctolagus cuniculus) classically conditioned nictitating membrane response.

Conditioned the nictitating membrane response to asymptote under identical experimental parameters in 3 groups of albino rabbits (N = 36). Subsequently, the 1st group was shifted to a longer modal intertrial interval (ITI) for further training, the 2nd group was switched to a shorter modal ITI, and the 3rd group was continued with intermediate ITI values. Results reveal (a) immediate incremental and decremental performance adjustments following the shift to longer and shorter modal ITIs, respectively, which were maintained over 10 postasymptotic sessions; (b) evidence of within-session performance decrements during postasymptotic conditioning; and (c) no evidence of retention losses in a retention test conducted 72 hr following the final conditioning session. (16 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Short-term retention of habituation in the rat: A developmental study from infancy to old age.

Allowed 168 infant, weanling, adult, and elderly Blue Spruce hooded and albino rats to habituate to a simple exploratory situation and then tested them for retention after 1 min, 1 hr, or 24 hrs. Infants habituated more slowly than older Ss as indicated by time to habituate and response frequency measures. No age differences were found after a 1-min retention interval, which suggests that the final levels of original habituation did not differ. However, after longer intervals (1 hr and 24 hrs), infants showed poorer retention of habituation than the older Ss. (17 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)