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PubMed2000

Flashbulb memories? The effects of when the initial memory report was obtained.

Why have some researchers found reports of flashbulb memories to be stable, while others have observed inconsistencies? Paradoxically, it appears that relatively long delays between event and initial documentation have produced greater consistency of participants' reports. To investigate this directly, we collected the initial documentation of hearing about O.J. Simpson's acquittal either five hours or one week after the acquittal was read. Observed consistency of memories varied as a function of documentation time; following an eight-week retention, the delayed reports were more consistent. The delayed group also reported fewer propositions in their initial documentation. We proposed a consolidation model to explain these results: during the days immediately following a newsworthy event, the narrative structure of these memories changes in that some details are forgotten. After this consolidation period, the memories may solidify. Thus, it may have been easier for the delayed group to provide consistent memories at the two intervals.

Adult↗

PubMed2002

Glucocorticoid involvement in memory formation in a rat model for traumatic memory.

Contextual fear conditioning under training conditions involving high stressor intensities has been proposed as an animal model for traumatic memories. The strength of memory for this task has been related to the intensity of the conditioning stressor and post-training corticosterone values. However, administration of a glucocorticoid receptor (GR) antagonist only attenuated memory for this task in rats conditioned at a moderate shock intensity (0.4 mA), but failed to influence conditioning in rats trained at a high shock intensity (1 mA). Here, we further questioned whether interfering with glucocorticoid action at the time of training might be effective in influencing contextual fear conditioning in rats trained under different shock intensities. Rats were subcutaneously injected with the glucocorticoid synthesis inhibitor metyrapone (50, 100 mg/kg) 90 min before being trained in the contextual fear conditioning task, at either 0.4 or 1 mA shock intensities. The results showed that metyrapone, in a dose-dependent manner: (i) attenuated long-term expression of contextual fear conditioning, both in 0.4- and 1 mA-trained rats; and (ii) efficiently prevented increased plasma corticosterone concentration. In addition to further supporting a facilitating role of glucocorticoids in memory consolidation, these findings suggest a critical involvement of these hormones in the formation of traumatic memories.

Animals↗

PubMed2005

Memory processing and the glucose facilitation effect: the effects of stimulus difficulty and memory load.

Previous research has consistently found enhancement of memory after the ingestion of a glucose containing drink. The aims of the present study were to specify more precisely the nature of this facilitation by examining the cognitive demand hypothesis. This hypothesis predicts greater glucose induced facilitation on tasks that require significant mental effort. In two experiments, both employing an unrelated sample design, participants consumed either 25 g of glucose or a control solution. In experiment 1, participants first studied low and high imagery word-pairs and memory was assessed 1-, 7- and 14-days later by cued recall. Overall, glucose enhanced both encoding and consolidation processes only for the more difficult low imagery pairs. In experiment 2, the degree of mental effort in a verbal memory task was manipulated in two ways: (1) by varying the phonological similarity of the words; and (2) by varying the length of word lists. Glucose was found to enhance memory only for longer word lists. These data are consistent with the idea that glucose is especially effective in demanding memory tasks, but place some limits on the forms of difficulty that are susceptible to enhancement.

Adolescent↗

PubMed1997

Scheduling processes in working memory: instructions control the order of memory search and mental arithmetic.

Humans must often use working memory to execute processes one at a time because of its limited capacity. Two experiments tested where limits in access to working memory occur. Subjects searched a short-term memory set for one stimulus digit and performed mental arithmetic with another stimulus digit. In one experiment, they were told to carry out the mental arithmetic before the memory search and to make the arithmetic response first. In the other, they were instructed to perform the tasks in the opposite order. The overt responses were executed in the prescribed order. Moreover, the covert working memory processes were executed in the prescribed order, as revealed by a critical path network analysis of reaction times. Results are explained in terms of a double-bottleneck model in which central processes and responses are constrained to be carried out for one task at a time.

Adult↗

PubMed1983

Suppressor T cell memory. II. The role of memory suppressor T cells in tolerance to human gamma globulin.

The transient presence of suppressor T cell (Ts) activity in high-dose tolerance to human gamma globulin (HGG), and its (apparent) absence in low-dose tolerance, have been advanced as strong evidence against the concept that Ts play an important role in maintenance of immunological unresponsiveness. To analyze this question, CBA mice were exposed to high or low doses of deaggregated HGG (dHGG) and later challenged with HGG in immunogenic form (aHGG); their capacity to mount a primary or secondary suppressive response was assessed in an adoptive hapten-carrier system. Primary suppression reached a maximum 7 d after high-dose tolerance induction and gradually waned thereafter, being no longer detectable by day 30-35. Subsequent challenge of tolerant mice with aHGG, however, led to a rapid reactivation of suppression that bore the hallmarks of an anamnestic secondary response, and this effect was still demonstrable 135 d after tolerance induction. It was also shown that a single low dose of dHGG was capable of generating memory for suppression despite the absence of detectable primary suppression, indicating that the latter is not a prerequisite for induction of memory cells. The results were interpreted as indicating that tolerance, like immunity, is a manifestation of specific immunological memory. If tolerance to self-antigens is maintained by a similar mechanism, it would be expected that memory Ts could be induced during the early stages of fetal development. Mice were therefore exposed to tolerogen in utero by injection of their mothers with dHGG at day 7 of gestation, and were assessed at various times after birth for the capacity to exhibit primary or secondary suppression in adoptive transfer. Nonspecific suppression masked any specific effects during the first 5 wk of life. Antigen-specific, primary suppression was demonstrable subsequently until 10-12 wk of age, and if the animals were challenged with aHGG before transfer an anamnestic secondary suppressive response could be elicited up to 6 mo of age. These observations are consistent with the notion that memory Ts may play an important role in the maintenance of self-tolerance.

Animals↗

PubMed2002

Oscillations in the alpha band (9-12 Hz) increase with memory load during retention in a short-term memory task.

To study the role of brain oscillations in working memory, we recorded the scalp electroencephalogram (EEG) during the retention interval of a modified Sternberg task. A power spectral analysis of the EEG during the retention interval revealed a clear peak at 9-12 Hz, a frequency in the alpha band (8-13 Hz). In apparent conflict with previous ideas according to which alpha band oscillations represent brain "idling", we found that the alpha peak systematically increased with the number of items held in working memory. The enhancement was prominent over the posterior and bilateral central regions. The enhancement over posterior regions is most likely explained by the well known alpha rhythm produced close to the parietal-occipital fissure, whereas the lateral enhancement could be explained by sources in somato-motor cortex. A time-frequency analysis revealed that the enhancement was present throughout the last 2.5 s of the 2.8 s retention interval and that alpha power rapidly diminished following the probe. The load dependence and the tight temporal regulation of alpha provide strong evidence that the alpha generating system is directly or indirectly linked to the circuits responsible for working memory. Although a clear peak in the theta band (5-8 Hz) was only detectable in one subject, other lines of evidence indicate that theta occurs and also has a role in working memory. Hypotheses concerning the role of alpha band activity in working memory are discussed.

Adolescent↗

PubMed1996

Age differences in episodic memory, semantic memory, and priming: relationships to demographic, intellectual, and biological factors.

This study examined age differences in episodic memory, semantic memory, and priming using a random sample of 1,000 men and women from 10 age groups (35, 40, 45, . . . 80 years). The main purpose was to determine whether an age effect existed after differences on various demographic, intellectual, and biological factors had been controlled for. The simple correlations of age with episodic and semantic memory performance were found to be significant, whereas no relationship was found between age and levels of priming. After controlling for differences on the background factors, age predicted episodic but not semantic memory performance. It is proposed that the failure to account for the age effect on episodic memory is because it is caused by age-related neuronal changes.

Adult↗

PubMed2004

Search for cognitive trait components of schizophrenia reveals a locus for verbal learning and memory on 4q and for visual working memory on 2q.

Research to identify predisposing genes for complex diseases relying solely on clinical diagnosis is probably not ideal. Here, we analyzed genome-wide data for 168 schizophrenia families using neuropsychological variables associated with disease susceptibility, with the aid of SOLAR, a program for variance-component analysis. The linkage signal was greatly accentuated by application of the quantitative traits compared with diagnosis. We found evidence for a locus for verbal learning and memory on 4q21 (Z=3.01, Z(mp)=3.84 and empiric P=0.031 for delayed memory; Z=2.96, Z(mp)=3.4 and P=0.026 for verbal learning) and suggestive evidence for visual working memory on 2q36 (Z=2.80, Z(mp)=2.08 and P=0.093). In addition, some evidence emerged for a locus for recognition memory on 10p13, visual attention on 15q22 and executive function on 9p22 in the complete sample, as well as for delayed memory on 8q12, semantic clustering and intrusions on 1q42 and visual attention on 3p25 in the genealogically distinctive sample subsets. Of the loci linked to schizophrenia in diverse populations, in addition to the earlier mentioned regions, some evidence of linkage was observed for 2q, 6q, 7q, 11q, 13q, 14q, 18q and 22q. Our results reveal initial information on the effect of the loci associated with schizophrenia in multiple studies, and emphasize the value of trait components in the search for susceptibility loci for complex diseases.

Analysis of Variance↗

PubMed2006

Neonate-primed CD8+ memory cells rival adult-primed memory cells in antigen-driven expansion and anti-viral protection.

Immunizations early in life, when the host is most susceptible to infection, allow protective immunological memory to develop. Decreasing the dose of Cas-Br-E murine leukemia virus when priming neonatal mice results in adult-like, Type 1 protective responses, but the resulting memory cell populations are smaller than after adult priming. After secondary challenge, virus-specific CD8+ memory cell populations expand twice as much in neonate-primed mice as in adult-primed mice. We found that when equivalent numbers of virus-specific cells were transferred into virus-susceptible mice, protection from disease was similar whether donor, immune mice were primed as neonates or adults, and IL-4 did not alter in vivo virus-specific CD8+ memory cell effector function. Hence, neonate-primed CD8+ cells develop into memory cells that rival adult-primed cells in proliferation and effector function.

Animals↗

PubMed2006

Emotional memories are not all created equal: evidence for selective memory enhancement.

Human brain imaging studies have shown that greater amygdala activation to emotional relative to neutral events leads to enhanced episodic memory. Other studies have shown that fearful faces also elicit greater amygdala activation relative to neutral faces. To the extent that amygdala recruitment is sufficient to enhance recollection, these separate lines of evidence predict that recognition memory should be greater for fearful relative to neutral faces. Experiment 1 demonstrated enhanced memory for emotionally negative relative to neutral scenes; however, fearful faces were not subject to enhanced recognition across a variety of delays (15 min to 2 wk). Experiment 2 demonstrated that enhanced delayed recognition for emotional scenes was associated with increased sympathetic autonomic arousal, indexed by the galvanic skin response, relative to fearful faces. These results suggest that while amygdala activation may be necessary, it alone is insufficient to enhance episodic memory formation. It is proposed that a sufficient level of systemic arousal is required to alter memory consolidation resulting in enhanced recollection of emotional events.

Adolescent↗

PubMed2003

Multiple visual memory phenomena in a memory search task.

This paper reports evidence of the existence of multiple and distinct visual memory processes in a memory search task in which a divided field stimulus presentation was used at study (Experiments 1-3) and either a foveal (Experiments 1 and 2) or a lateralized (Experiment 3) stimulus presentation was used at test. These memory processes can be distinguished on the basis of (1) whether or not they are hemispherically organized; and (2) the locus of their underlying brain activity, as evidenced by the scalp distribution of the event-related brain potentials and by the localization of the event-related optical signal that accompany them. These memory effects are discussed in the context of visual form memory.

Adult↗

PubMed2004

Short-term episodic memory for visual textures: a roving probe gathers some memory.

Cognition is shaped by the way that past experiences are represented in memory. To examine the representation of recent visual experiences, we devised a novel procedure that measures episodic recognition memory for synthetic textures. On each trial, two brief study stimuli were followed by a probe, which either replicated one of the study stimuli or differed in spatial frequency from both. The probe's spatial frequency roved from trial to trial, testing recognition with a range of differences between probe and study items. Repeated testing of recognition generated mnemometric functions, snapshots of memory strength's distribution. The distributional characteristics of the mnemometric functions rule out several hypotheses about memory representation, including the hypothesis that representations are prototypes constructed from previously seen stimuli; instead, stimuli are represented in memory as noisy exemplars.

Adult↗

PubMed1986

Intestinal mucosal memory and presence of memory cells in lamina propria and Peyer's patches in mice 2 years after oral immunization with cholera toxin.

The build-up of long-term immunological memory in the gut mucosal immune system may explain long-lasting protection against new attacks of cholera in convalescents from natural disease. We have looked for gut mucosal antitoxin immunological memory and memory cells in mice after oral immunization with cholera toxin. Our results show that mice that were orally primed with cholera toxin and then boosted 2 years later with a single oral antigen dose mounted a rapid and vigorous IgA antitoxin response in the intestinal lamina propria. A specific secondary antitoxin response could also be elicited without any in-vivo boosting by in-vitro stimulation of isolated lymphocytes from the lamina propria, Peyer's patches, mesenteric lymph nodes, and spleen. The results provide evidence for the almost life-long persistence of anti-cholera toxin memory B cells (and perhaps also T cells) in the intestine and probably also recirculating cells, after oral immunization with cholera toxin. A functional antitoxic immune response may be boosted rapidly on renewed enteral exposure to cholera toxin by the stimulation of memory cells both in the lamina propria and in the Peyer's patches.

Administration, Oral↗

PubMed1981

Self-ratings of memory versus psychometric ratings of memory and hypochondriasis.

Self-ratings of memory were studied in 69 institutionalized women. The patients also were evaluated by means of three screening tests for organic brain syndrome (OBS) and a hypochondriasis scale. A negative correlation existed between self-rating of memory and actual memory as measured by the screening tests for OBS, but it was significant (p less than .05) for only one of the tests. There was also a negative correlation (p less than .01) between memory rating and scores on the hypochondriasis scale. Therefore, clinicians should not take patients' memory complaints as valid indicators of OBS, but as possible indicators of hypochondriasis.

Aged↗

PubMed2006

Disputes over memory ownership: What memories are disputed?

The ownership of memories is sometimes disputed, particularly by twins. Examination of 77 disputed memories, 71 provided by twins, showed that most of the remembered events are negative and that the disputants appear to be self-serving. They claim for themselves memories for achievements and suffered misfortunes but are more likely to give away memories of personal wrongdoing. The research suggests that some of the memories in which we play a leading role might in fact have been the experiences of others.

Adolescent↗

PubMed1998

Are odors the best cues to memory? A cross-modal comparison of associative memory stimuli.

To test the claim that odors are the 'best' cues to memory, several cross-modal experiments were conducted in which odors were compared with verbal, visual, tactile and musical stimuli as associated memory cues. Each experiment comprised two sessions (encoding and retrieval) separated by 48 hr. At the encoding session, a series of stimuli were incidentally associated to a set of emotionally arousing pictures. At the retrieval session, memory accuracy and emotionality were assessed. Across experiments, results revealed that odors were equivalent to other stimuli in their ability to elicit accurate recall, but that odor-evoked memories were always more emotional. Notably, emotional responses did not vary as a function of stimulus type at encoding. These data indicate that emotional saliency, rather than accuracy, is responsible for the impression that odors are superior reminders, and that retrieval processes (cf. encoding processes) are responsible for the distinctive emotionality of odor-evoked memories.

Adolescent↗

PubMed1998

Memory suppressor genes: inhibitory constraints on the storage of long-term memory.

Synaptic plasticity, the ability of neurons to alter the strength of their synaptic connections with activity and experience, is thought to play a critical role in memory storage. Molecular studies of gene expression during long-lasting synaptic plasticity related to memory storage initially focused on the identification of positive regulators. More recent work has revealed that the establishment of long-lasting synaptic plasticity and long-term memory also requires the removal of inhibitory constraints. By analogy to tumor suppressor genes, which restrain cell proliferation, we propose that these inhibitory constraints of memory storage, which restrain synapse growth, be termed memory suppressor genes.

Activating Transcription Factor 2↗

PubMed1994

Self-reported memory complaints and memory performance in elderly French community residents: results of the PAQUID Research Program.

An epidemiological survey of self-reported memory complaints and memory performance [assessed with Benton's visual-retention test (BVRT) and the Wechsler paired-associates test (WPAT)] was undertaken in a community sample of 2,726 noninstitutionalized subjects aged 65 and over living in Gironde (southwestern France). A significant relationship was observed between the presence of self-reported memory problems and lower performance on the BVRT and the WPAT. However, beyond this relationship, there was significant discordance between the two evaluations, explained in part by the fact that the correlates of memory functioning were not related with similar strength to self reports and to actual performance. In general, females and subjects who scored above the depressive symptomatology threshold reported more problems, while lower performances were related to older age and low educational level. The discordance between self reports and actual performance may suggest anosognosia of mild memory deficits and could possibly be a predictor of future intellectual deterioration.

Aged↗