Very long-term memory for knowledge acquired at school and university

Recent research into the very long-term retention of knowledge originally acquired during the process of formal education at school and university has demonstrated that such knowledge may be retained at high levels over very long retention intervals. The pattern of retention typically takes the form of a comparatively short period marked by forgetting (lasting between 1 and 6 years) followed by a long period of stable retention (usually longer than 30 years). For courses taken at school the level attained over a series of courses (e.g. in learning a foreign language or studying mathematics) is an important determinant of long-term retention. Students who attain moderate or advanced levels of learning show high levels of retention with very little forgetting, whereas students who attain only lower levels of learning show steady forgetting, and after a period of 6 years retain very little knowledge. Similar patterns of retention are present for university students taking single courses in science and literature subjects, and students with higher grades retain more knowledge although the reliable relationship here, between grade obtained and amount remembered, is weak and accounts for only small portions of the variance in retention. Taken together these findings suggest that the retention of knowledge acquired through formal education persists over longer periods of time than popularly believed. Recent theory proposes that these long-lasting effects of education are partly related to the types of learning schedules followed during acquisition and partly related to the nature of the to-be-acquired knowledge, and to whether or not knowledge can be represented schematically.     

Learning at the breast: preference formation for an artificial scent and its attraction against the odor of maternal milk

Human newborns are known to display spontaneous attraction to the odor of human milk. This study aimed to assess whether the positive response to human milk odor can be explained by nursing-related learning, and whether it can be easily reassigned to a novel odor associated with nursing. Infants were exposed or not to a novel odor (camomile, Ca) during nursing, and tested on day 3-4 for their preference for camomile in comparison with either a scentless control (Exp. 1), a scented control (Exp. 2), or maternal milk (Exp. 3). Prior experience with Ca modified the newborns' responses. While the Ca odor became more attractive than a scented control in the Ca-exposed group, the Ca-non-exposed group did not differentiate either stimulus. In Exp. 3, the Ca-non-exposed group preferred the milk odor to the Ca odor, whereas the Ca-exposed group displayed on average equal attraction to both stimuli. Thus, a novel odor can be learned at the breast, and gain similar attractive power than the odor of mother's milk. In sum, reinforcements related with the early episodes of breastfeeding mediate the rapid development of novel odor preferences in human infants.     

Affective priming as an indirect measure of food preferences acquired through odor conditioning

The present study aimed at investigating affective priming for originally neutral food stimuli that recently acquired their affective meaning through odor conditioning. In a first phase, pictures of different brands of yogurts (CSs) were contingently presented with a positive or negative odor (US). In a subsequent phase, the yogurt CSs were used as primes in an affective priming procedure. Rating data showed that the acquisition procedure resulted in a reliable evaluative learning effect. This could be corroborated by the results of the priming task. Participants responded faster to positive target words and made fewer errors when they were preceded by a CS that had been associated with a positive odor, as compared to a CS that was associated with a negative odor. A reversed pattern was present for negative targets. Based on these findings, it is suggested that affective priming might be used as a demand-free measure of evaluative learning.     

Depletion of serotonin selectively impairs short-term memory without affecting long-term memory in odor learning in the terrestrial slug Limax valentianus

The terrestrial slug Limax is able to acquire short-term and long-term memories during aversive odor-taste associative learning. We investigated the effect of the selective serotonergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) on memory. Behavioral studies indicated that 5,7-DHT impaired short-term memory but not long-term memory. HPLC (high-performance liquid chromatography) analysis revealed that 5,7-DHT significantly reduced serotonin content in the central nervous system. The present study suggests that acquisition, retention, and/or retrieval of short-term memory involves serotonin, and neither acquisition nor retrieval of long-term memory requires serotonin at a level as high as that required for short-term memory.     

Inactivation of the basolateral amygdala impairs the retrieval of recent and remote taste-potentiated odor aversion memory

Memory reorganization as a time-dependent process can be investigated using various learning tasks such as the taste-potentiated odor aversion (TPOA). In this paradigm rats acquire a strong aversion to an olfactory cue presented simultaneously with a gustatory cue. Together these cues are paired with a delayed visceral illness. The basolateral amygdaloid nucleus (BLA) plays a key role in TPOA acquisition but its involvement in retrieval remains unclear. We investigated the involvement of the BLA in either recent or remote retrieval of TPOA. In each case, the number of licks observed in response to the presentation of either the odor or the taste was used to assess retrieval. Before the retrieval test, rats received a bilateral infusion of lidocaine to inactivate the BLA. We observed that both recent and remote TPOA retrieval tests induced by the odor presentation were disrupted in the lidocaine-injected rats. By contrast, the BLA inactivation had no effect upon the aversion towards the taste cue regardless of the time of retrieval. The present study provides evidence that BLA functioning is necessary for retrieval of aversive odor memory, even with a long post-acquisition delay.     

Long-lasting and context-specific freezing preference is acquired after spaced repeated presentations of a danger stimulus in the crab Chasmagnathus

A visual danger stimulus elicits an escape response in the crab Chasmagnathus that declines after repeated presentations. Previous results report that such waning may be retained as context-signal memory (CSM) or signal memory (SM): CSM is long lasting, associative, and produced by spaced training, while SM is an intermediate memory, nonassociative, and produced by massed training. The performances of both spaced and massed trained crabs are here examined, using video analysis to determine topographic changes in the behavioral response during and after training. During spaced training, escape vanishes and is mainly replaced by freezing, while during massed training, escape decreases over trials without being replaced by any defensive response. After 24 h, the marked proclivity to freezing persists in spaced trained crabs, while a high level of escaping is shown by massed trained crabs. The long-lasting freezing preference of spaced trained crabs proves to be context-specific and apparent from the very first presentation of the danger stimulus at testing, though freezing is not triggered by the sole exposure to the context. We conclude (a) that freezing preference is the acquired response of the CSM process; (b) that CSM can be properly categorized as an instance of contextual conditioning and SM of classical habituation; (c) that CSM and SM are not two phases of a memory processing but two distinctly types of memory; and (d) that therefore, the temporal distribution of training trials has a drastic effect on crab's memory, more dramatic than that previously described. The possibility that massed and spaced presentations of the same stimulus may represent two different stimulus types is discussed.     

What a nostril knows: olfactory nerve-evoked AMPA responses increase while NMDA responses decrease at 24-h post-training for lateralized odor preference memory in neonate rat

Increased AMPA signaling is proposed to mediate long-term memory. Rat neonates acquire odor preferences in a single olfactory bulb if one nostril is occluded at training. Memory testing here confirmed that only trained bulbs support increased odor preference at 24 h. Olfactory nerve field potentials were tested at 24 h in slices from trained and untrained bulbs. A larger AMPA component and a smaller NMDA component characterized responses in the bulb receiving odor preference training. Field potential changes were not seen in a bulbar region separate from the lateral odor-encoding area. These results support models in which memory is mediated by increased olfactory nerve-mitral cell AMPA signaling, and memory stability is promoted by decreased NMDA-mediated signaling.     

Incidental memory in dogs (Canis familiaris): adaptive behavioral solution at an unexpected memory test

Memory processing in nonhuman animals has been typically tested in situations where the animals are repeatedly trained to retrieve their memory trace, such as delayed matching to sample, serial probe recognition, etc. In contrast, how they utilize incidentally formed memory traces is not well investigated except in rodents. We examined whether domestic dogs could solve an unexpected test based on a single past experience. In Experiment 1, leashed dogs were led to 4 open, baited containers and allowed to eat from 2 of them (Exposure phase). After a walk outside for more than 10?min, during which time the containers were replaced with new identical ones, the dogs were unexpectedly returned to the site and unleashed for free exploration (test phase). Eleven out of 12 dogs first visited one of the containers from which they had not eaten. In Experiment 2, two containers had food in them, one had a nonedible object, and the last one was empty. Dogs visited all 4 containers and were allowed to eat one of the food rewards in the Exposure phase. In the test phase, unleashed dogs first visited the previously baited container from which they had not eaten significantly more often than chance. These results demonstrate that in an unexpected, test dogs may retrieve “what” and “where” information about seen (now invisible) items from incidental memory formed during a single past experience.     

Psychosocial stress impairs working memory at high loads: an association with cortisol levels and memory retrieval

Stress and cortisol are known to impair memory retrieval of well-consolidated declarative material. The effects of cortisol on memory retrieval may in particular be due to glucocorticoid (GC) receptors in the hippocampus and prefrontal cortex (PFC). Therefore, effects of stress and cortisol should be observable on both hippocampal-dependent declarative memory retrieval and PFC-dependent working memory (WM). In the present study, it was tested whether psychosocial stress would impair both WM and memory retrieval in 20 young healthy men. In addition, the association between cortisol levels and cognitive performance was assessed. It was found that stress impaired WM at high loads, but not at low loads in a Sternberg paradigm. High cortisol levels at the time of testing were associated with slow WM performance at high loads, and with impaired recall of moderately emotional, but not of highly emotional paragraphs. Furthermore, performance at high WM loads was associated with memory retrieval. These data extend previous results of pharmacological studies in finding WM impairments after acute stress at high workloads and cortisol-related retrieval impairments.     

Overgeneral autobiographical memory in adolescents at risk for depression

Autobiographical memory functioning is implicated in the course and onset of depression in adults (Williams et al., 2007), and there is preliminary evidence that adolescents with a diagnosis of depression have a bias towards retrieving overgeneral autobiographical memories (Kuyken & Howell, 2006; Kuyken, Howell, & Dalgleish, 2006; Park, Goodyer, & Teasdale, 2002). In two independent studies we asked whether adolescents at risk for depression exhibit autobiographical memory deficits. In the first community study of 179 adolescents, risk was operationalised as higher scores on neuroticism. We found that neuroticism was associated with greater retrieval of categoric memories to negative cue words and that severity of depressive symptoms mediated this relationship. In the second study, groups of formerly depressed (n=15) and never depressed adolescents (n=15) were matched on age, gender, depressive symptoms and verbal fluency, and again compared on their autobiographical memory functioning. Mirroring the findings from Study 1 we found that risk, operationalised here as a history of depression in remission, was associated with greater retrieval of categoric memories to negative cue words. Taken together, these studies show that risk for depression is associated with a greater tendency to retrieve categoric memories to negative cue words and suggest that autobiographical retrieval may be implicated in onset of depression in adolescence.     

Sharpening the echo: an iterative-resonance model for short-term recognition memory

We present an iterative-resonance model for recognition memory. On successive iterations, the probe is compared against a feature-by-feature profile of the study set. Yes decisions depend on the similarity of the probe to the profile; No decisions depend on a count of elements in the probe that are not in the profile. Successive iterations sharpen the evidence, and response latency is a function of the number of iterations needed to obtain a sufficiently clear result. The model successfully simulates classic data as well as recent data problematic for alternate models.     

Neonatal odor-shock conditioning alters the neural network involved in odor fear learning at adulthood

Adult learning and memory functions are strongly dependent on neonatal experiences. We recently showed that neonatal odor-shock learning attenuates later life odor fear conditioning and amygdala activity. In the present work we investigated whether changes observed in adults can also be observed in other structures normally involved, namely olfactory cortical areas. For this, pups were trained daily from postnatal (PN) 8 to 12 in an odor-shock paradigm, and retrained at adulthood in the same task. (14)C 2-DG autoradiographic brain mapping was used to measure training-related activation in amygdala cortical nucleus (CoA), anterior (aPCx), and posterior (pPCx) piriform cortex. In addition, field potentials induced in the three sites in response to paired-pulse stimulation of the olfactory bulb were recorded in order to assess short-term inhibition and facilitation in these structures. Attenuated adult fear learning was accompanied by a deficit in 2-DG activation in CoA and pPCx. Moreover, electrophysiological recordings revealed that, in these sites, the level of inhibition was lower than in control animals. These data indicate that early life odor-shock learning produces changes throughout structures of the adult learning circuit that are independent, at least in part, from those involved in infant learning. Moreover, these enduring effects were influenced by the contingency of the infant experience since paired odor-shock produced greater disruption of adult learning and its supporting neural pathway than unpaired presentations. These results suggest that some enduring effects of early life experience are potentiated by contingency and extend beyond brain areas involved in infant learning.     

Memory states and memory tasks: an integrative framework for eyewitness memory and suggestibility

An integrative framework (IMP) is presented which depicts performance in eyewitness suggestibility experiments as the participants' solutions of memory tasks, depending on (a) a specified task-relevant memory base and (b) the participants' perception of the memory task. Three theoretical explanations of the effect of misleading post-event information are reinterpreted and reduced to one single core: individuals answer test questions while assuming the consistency of event and post-event information. The impact of such consistency assumptions (a) is demonstrated in a first experiment, where the usual misinformation effect obtained with the Loftus standard test procedure disappeared when the participants' consistency assumptions were destroyed prior to testing, and (b) manifests itself in a qualitative analysis of individual processing strategies for discrepancies between details. Experiment 2, employing methodological innovations suggested by IMP, examined the memory base and found no evidence for memory impairment or misattributions of post-event details to the witnessed scene. However, a follow-up study conducted four and a half months later revealed a strong tendency for such misattributions which might indicate long-term integration of information.     

Cycloheximide produces amnesia for extinction and reconsolidation in an appetitive odor discrimination task in rats

A considerable literature has shown deficits in memory resulting from the administration of protein synthesis inhibitors; however, most of the past literature in this field has focused on acquisition of new memory using aversively-motivated tasks. The effect of protein synthesis inhibition on appetitive learning and memory as well as extinction is less clear. The present study employed an appetitive odor discrimination paradigm to examine the effects of acute cycloheximide administration (1 mg/kg) on reconsolidation and extinction.Male, Long-Evans adult rats were trained to discriminate between two odors (i.e., cocoa and cinnamon) and then received extinction trials following an intraperitoneal injection of cycloheximide or vehicle. Twenty-four hours later, rats were tested via one non-reinforced test trial. Results showed amnesia for extinction as well as original training (i.e., correct odor choice) in cycloheximide-injected rats in this appetitive task, while vehicle-injected controls showed good memory for extinction. These data add to a growing literature showing the importance of protein synthesis inhibition for extinction and reconsolidation in appetitive learning and memory.     

Emotional context at learning systematically biases memory for facial information

Emotion influences memory in many ways. For example, when a mood-dependent processing shift is operative, happy moods promote global processing and sad moods direct attention to local features of complex visual stimuli. We hypothesized that an emotional context associated with to-be-learned facial stimuli could preferentially promote global or local processing. At learning, faces with neutral expressions were paired with a narrative providing either a happy or a sad context. At test, faces were presented in an upright or inverted orientation, emphasizing configural or analytical processing, respectively. A recognition advantage was found for upright faces learned in happy contexts relative to those in sad contexts, whereas recognition was better for inverted faces learned in sad contexts than for those in happy contexts. We thus infer that a positive emotional context prompted more effective storage of holistic, configural, or global facial information, whereas a negative emotional context prompted relatively more effective storage of local or feature-based facial information     

Long-term memory for the emotional gist and the emotional essence of an experience

We investigated accuracy in recalling past emotional behaviours and emotionality. Male couples discussed the history of their relationship, and coders rated the extent to which each partner engaged in behaviours such as complimenting or criticising. These ratings were combined into dimensions representing the deeper, emotional essence of that partner's discussion (expressions of We-ness, Fondness, Negativity, and Disappointment). Four years later, participants accurately recalled some of their own and some of their partner's emotional gist-level behaviours, but their answers indicated that they also remembered the emotional essence of the conversation. We conclude that individuals can retain the emotional essence of an experience for a long time, and that they may use this memory to infer, in part, gist-level details of the experience.     

Working memory at work: how the updating process alters the nature of working memory transfer

In three N-Back experiments, we investigated components of the process of working memory (WM) updating, more specifically access to items stored outside the focus of attention and transfer from the focus to the region of WM outside the focus. We used stimulus complexity as a marker. We found that when WM transfer occurred under full attention, it was slow and highly sensitive to stimulus complexity, much more so than WM access. When transfer occurred in conjunction with access, however, it was fast and no longer sensitive to stimulus complexity. Thus the updating context altered the nature of WM processing: The dual-task situation (transfer in conjunction with access) drove memory transfer into a more efficient mode, indifferent to stimulus complexity. In contrast, access times consistently increased with complexity, unaffected by the processing context. This study reinforces recent reports that retrieval is a (perhaps the) key component of working memory functioning.     

Long-lasting attentional influence of negative and taboo words in an auditory variant of the emotional Stroop task

Using an auditory adaptation of the emotional and taboo Stroop tasks, the authors compared the effects of negative and taboo spoken words in mixed and blocked designs. Both types of words elicited carryover effects with mixed presentations and interference with blocked presentations, suggesting similar long-lasting attentional effects. Both were also relatively resilient to the long-lasting influence of the preceding emotional word. Hence, contrary to what has been assumed (Schmidt & Saari, 2007), negative and taboo words do not seem to differ in terms of the temporal dynamics of the interdimensional shifting, at least in the auditory modality.     

Evidence for the substantia nigra pars compacta as an essential component of a memory system independent of the hippocampal memory system

The aim of the present study was to test if the nigrostriatal pathway is an essential component for a water maze cued task learning and if it works independently of the hippocampal memory system. This hypothesis was tested using an animal model of Parkinson's disease in which male Wistar rats were lesioned in the substantia nigra pars compacta (SNc) by the intranigral infusion of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), thus causing a partial depletion of striatal dopamine. SNc-lesioned and sham-operated animals were implanted bilaterally with guide cannulae above the dorsal hippocampus in order to be tested after the administration of 0.4 microl 2% lidocaine or saline into this structure. The animals were tested in a spatial or in a cued version of the water maze, memory tasks previously reported to model hippocampal-dependent spatial/relational and striatal-dependent S-R learning, respectively. Hippocampal inactivation, but not SNc lesion, impaired learning and memory in the spatial version of the water maze. An opposite situation was observed with the cued version. No significant interaction was observed between the SNc lesion and hippocampal inactivation conditions affecting scores in the spatial or in the cued version of the water maze. These results suggest that the nigrostriatal pathway is an essential part of the memory system that processes S-R learning and that it works independently of the hippocampal memory system that processes spatial/relational memories.