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PubMed2000

High-speed memory scanning: a behavioral argument for a serial oscillatory model.

In order to account for the memory span [G.A. Miller, The magical number seven, plus minus two: some limits on our capacity for processing information, Psychol. Rev. 63 (1956) 81-97.], the magical number seven, plus minus two, and high-speed scanning in human memory ¿S. Sternberg, High speed scanning in human memory, Science 153 (1966) 652-654., Lisman and collaborators [O. Jensen, J.E. Lisman, An oscillatory short-term memory buffer model can account for data on the Sternberg task, J. Neurosci. 18 (1998) 10688-10699; J.E. Lisman, M.A.P. Idiart, Storage of 7+/-2 short-term memories in oscillatory subcycles, Science 267 (1995), 1512-1515.] proposed an oscillatory short-term memory buffer model. In this neurophysiological model: "a single brain network can separately maintain up to seven memories by a multiplexing mechanism that uses theta and gamma brain oscillations for clocking. A memory is represented by groups of neurons that fire in the same gamma cycle" ¿O. Jensen, J.E. Lisman, An oscillatory short-term memory buffer model can account for data on the Sternberg task, J. Neurosci. 18 (1998) 10688-10699, p. 10688. To test this model, we tried to modify the memory scanning time by shifting the gamma oscillation frequency. To this aim, we replicated the visual short-term memory scanning task ¿S. Sternberg, High speed scanning in human memory, Science 153 (1966) 652-654., and we simultaneously used the protocol that Treisman ¿M. Treisman, A. Faulkner, P.L.N. Naish, D. Brogan, The internal clock: evidence for a temporal oscillator underlying time perception with some estimates of its characteristics frequency, Perception 19 (1990) 705-743. designed to drive, slowing down or speeding up, a temporal oscillator acting in the gamma range ¿J.G.R. Jefferys, R.D. Traub, M.A. Whittington, Neuronal networks for induced "40 Hz rhythms, Trends Neurosci. 19 (1996) 202-208; W. MacKay, Synchronized neuronal oscillations and their role in motor processes, Trends Cog. Sci. 1 (1997) 176-183; M. Treisman, N. Cook, P.L.N. Naish, J.K. MacCrone, The internal clock: electroencephalographic evidence for oscillatory processes underlying time perception, Q. J. Exp. Psychol. 47A (1994) 241-289.. In this protocol, an auditory periodic stimulus (click train) was delivered at various frequencies during the task. The reaction time (RT), the slope, and the intercept of the linear function associating RT to memorized list length showed systematic modulations according to the stimulation frequency. The predicted driving effects due to the click trains were obtained, consisting of localised modulations of performance on the stimulation frequency band. We argue that memory scanning is indeed paced by a temporal oscillator, thus providing behavioral arguments for the serial oscillatory model of Lisman.

Adult↗

PubMed2003

Nicotinic mechanisms of memory: effects of acute local DHbetaE and MLA infusions in the basolateral amygdala.

Nicotine has been shown to improve working memory. The neural mechanisms underlying this effect are still being determined. The ventral hippocampus is critical for nicotinic effects on memory. Local ventral hippocampal infusions of either the nicotinic alpha7 nicotinic receptor antagonist methyllycaconitine (MLA) or the alpha4beta2 nicotinic receptor antagonist dihydro-beta-erythroidine (DHbetaE) caused working memory impairments, but no additive effects were seen. Other areas, such as the amygdala, also likely play important roles in nicotinic effects on memory. Amygdalar lesions cause memory impairment and there is a dense concentration of nicotinic receptors in the basolateral amygdala. The current study used local basolateral amygdalar infusions of the nicotinic antagonists MLA and DHbetaE to determine the involvement of alpha7 and alpha4beta2 nicotinic receptors in spatial working and reference memory. Rats (n=8) were trained in the 16-arm radial maze and were implanted with bilateral infusion cannulae into the basolateral amygdala. Acute infusions of MLA (6.75 micro g/side, P<0.0005) or DHbetaE (3.38 micro g/side, P<0.025) caused significant working memory impairments. When given together MLA and DHbetaE did not produce an additive effect. In fact, the 6.75 micro g/kg dose of DHbetaE produced a significant (P<0.0005) attenuation of the MLA-induced working memory impairment. Significant effects were not seen with reference memory or response latency. Nicotinic systems in the basolateral amygdala, as in the ventral hippocampus, are important for spatial working memory. In both the basolateral amygdala and the ventral hippocampus, MLA and DHbetaE individually caused working memory impairments. The lowest effective dose of DHbetaE was lower in the basolateral amygdala than in the ventral hippocampus. In both the basolateral amygdala and the ventral hippocampus, combined MLA and DHbetaE treatment did not produce additive working memory deficits. Unlike in the ventral hippocampus, the addition of DHbetaE to MLA in the basolateral amygdala significantly reduced the MLA-induced working memory deficit.

Aconitine↗

PubMed2001

Comparing recollective experience in true and false autobiographical memories.

This study investigated whether true autobiographical memories are qualitatively distinct from false autobiographical memories using a variation of the interview method originally reported by E. F. Loftus and J. Pickrell (1995). Participants recalled events provided by parents on 3 separate occasions and were asked to imagine true and false unremembered events. True memories were rated by both participants and observers as more rich in recollective experience and were rated by participants as more important, more emotionally intense, as having clearer imagery, and as less typical than false memories. Rehearsal frequency was used as a covariate, eliminating these effects. Imagery in true memories was most often viewed from the field perspective, whereas imagery in false memories was most often viewed from the observer perspective. More information was communicated in true memories, and true memories contained more information concerning the consequences of described events. Results suggest repeated remembering can make false memories more rich in recollective experience and more like true memories. Differences between true and false memories suggest some potentially distinct characteristics of false memories and provide insight into the process of false memory creation.

Adult↗

PubMed1999

Lateralized memory deficits on the Wada test correlate with the side of lobectomy only for patients with unilateral medial temporal lobe epilepsy.

The aim of this study was to determine whether the predictive value of the intracarotid amobarbital test (IAT) for the side to be resected is applicable only to medial temporal lobe epilepsy and to investigate whether there are different patterns of memory performances on the IAT between patients with unilateral mesial temporal sclerosis (UMT group) and those without (non-UMT group). We studied 30 patients in the UMT group and 10 in the non-UMT group, who underwent pre-surgical evaluation for intractable temporal lobe epilepsy. Memory performances on the IAT was defined as the percentage of memory items presented during unilateral hemispheric anesthesia that was recognized after recovery. More than a 20% decline of the memory performance on the IAT compared with the memory performance on the pre-test was regarded as a memory deficit. Age at onset of epilepsy was significantly younger in the UMT than in the non-UMT group. Surgical outcome was significantly better in the UMT than in the non-UMT group. The lateralizing value of unilateral memory deficits on the IAT was statistically confirmed. There was a significant association between falsely lateralizing memory performances and the non-UMT group. Excluding the exceptional cases with right-sided language dominance in spite of right-sided lesions, the high incidence of the unilateral right-sided memory deficits in the non-UMT group was statistically significant. This study suggested that the excellent lateralizing value of the memory performances on the IAT is limited to patients with mesial temporal lobe epilepsy. IAT memory performances in patients without such lesions can be misleading, even if lateralized, because their memory status presumably reflects a natural lateralization of the memory organization which is independent of the epileptogenic focus.

Adult↗

PubMed2006

Directly reactivated, but not indirectly reactivated, memories undergo reconsolidation in the amygdala.

Memory consolidation refers to a process by which newly learned information is made resistant to disruption. Traditionally, consolidation has been viewed as an event that occurs once in the life of a memory. However, considerable evidence now indicates that consolidated memories, when reactivated through retrieval, become labile (susceptible to disruption) again and undergo reconsolidation. Because memories are often interrelated in complex associative networks rather than stored in isolation, a key question is whether reactivation of one memory makes associated memories labile in a way that requires reconsolidation. We tested this in rats by creating interlinked associative memories using a second-order fear-conditioning task. We found that directly reactivated memories become labile, but indirectly reactivated (i.e., associated) memories do not. This suggests that memory reactivation produces content-limited rather than wholesale changes in a memory and its associations and explains why each time a memory is retrieved and updated, the entire associative structure of the memory is not grossly altered.

Amygdala↗

PubMed2004

The impact of sex and language dominance on material-specific memory before and after left temporal lobe surgery.

Recent findings raised evidence that in early-onset left temporal lobe epilepsy, women show greater functional plasticity for verbal memory than men. In particular, women with lesion- or epilepsy-driven atypical language dominance show an advantage over men. The question asked in this study was whether there is evidence of sex- and language dominance-dependent late, i.e. adult age, plasticity for verbal memory when epilepsy surgery is performed in these patients. Pre- and 1-year postoperative memory performance was evaluated in 169 patients (94 males and 75 females) who underwent left temporal lobe surgery and who had WADA testing of hemispheric language dominance prior to surgery. Verbal memory and figural memory were assessed by list-learning paradigms. According to the Bonn intracarotid amobarbital test (IAT) protocol, patients were categorized into left dominant or atypically dominant (right, incomplete left or right, and bilateral dominant) groups. Results were controlled for the hypothesized sex differences. Thirty-four percent of men and 47% of women displayed patterns of atypical language dominance. Atypical dominance was related to an early onset of epilepsy. Men showed a larger time window for development of atypical dominance but, differently from women, the pattern of atypical dominance was more strictly determined by the age at onset of epilepsy. Atypically dominant women showed better verbal memory than typically dominant women or men. After surgery, right dominant patients had better verbal memory outcome than patients with bilateral or left language dominance who showed significant memory loss. No effect of sex on verbal memory change was found. Figural memory deteriorated in men and improved in women, when they were not left dominant. Seizure outcome had no effect on performance changes. It was concluded that better preserved verbal memory in atypically dominant women before surgery indicates greater benefit from atypical dominance in women than men with regard to the initial damage associated with left hemisphere epilepsy. Later in life, when epilepsy surgery causes additional damage, no such sex difference is observed, indicating that the women's advantage over men is fixed to an early time window in life. Postoperative changes in figural memory suggest dynamics in crowding and suppression patterns. Whether this reflects late plasticity and compensation needs further demonstration. For clinical practice, it is important to note that incomplete right hemisphere and bilateral language dominance do not protect against verbal memory loss after left-sided temporal lobe surgery.

Adult↗

PubMed1992

Effects of isoflurane and nitrous oxide in subanesthetic concentrations on memory and responsiveness in volunteers.

Awareness, defined as conscious memory during anesthesia, has been a problem in anesthesia practice. To determine the effect of isoflurane and nitrous oxide (N2O) on memory, 17 healthy adult volunteers were randomly assigned to receive isoflurane or N2O and received the alternate agent 1-2 weeks later. Each volunteer was studied at four end-tidal concentrations of each agent, consecutively 0.15, 0.3, 0.45, and 0.15 times the minimum alveolar concentration (MAC) for isoflurane or 0.3, 0.45, 0.6, and 0.3 times MAC for N2O. After 15-min equilibration at each end-tidal concentration, volunteers were tested for voluntary response to command and were presented with verbal information to be recalled after anesthesia. Volunteers were interviewed on the day after the study and tested for conscious and unconscious memory of the information presented during anesthetic administration. MAC-awake (the end-tidal concentration preventing voluntary response in 50% of volunteers) was 0.38 (0.35-0.42) times MAC for isoflurane and 0.64 (0.61-0.68) MAC for N2O (means, 95% confidence limits), indicating isoflurane to be more potent than N2O in suppressing voluntary response (P = .0001). Memory data were analyzed in 12 volunteers who completed the study and in whom the allocation of information to be recalled was counterbalanced among agents and concentrations of agents. Memory was decreased by increasing concentrations of both agents. Conscious memory of the information presented during anesthetic administration was prevented by 0.45 MAC isoflurane but not completely prevented by 0.6 MAC N2O. Unconscious memory (defined as memory of information without conscious recognition) occurred during administration of both agents and was prevented by 0.45 MAC isoflurane but not by 0.6 MAC N2O. Isoflurane was more potent in suppressing memory than MAC-equivalent concentrations of N2O. Using models of the relationship between dose of agent and suppression of memory, a dose of both agents was estimated that suppressed memory by 50% (ED50). The ED50 was 0.20 MAC for isoflurane (95% confidence intervals, 0.15-0.25), and 0.50 MAC for N2O (95% confidence intervals 0.43-0.55). We conclude that isoflurane and N2O suppress memory in a dose-dependent manner, and that isoflurane is more potent in preventing memory and voluntary response to command than MAC-equivalent concentrations of N2O.

Adolescent↗

PubMedDate not supplied

Theta/gamma networks with slow NMDA channels learn sequences and encode episodic memory: role of NMDA channels in recall.

This paper examines the role of slow N-methyl-D-aspartate (NMDA) channels (deactivation approximately 150 msec) in networks that multiplex different memories in different gamma subcycles of a low frequency theta oscillation. The NMDA channels are in the synapses of recurrent collaterals and govern synaptic modification in accord with known physiological properties. Because slow NMDA channels have a time constant that spans several gamma cycles, synaptic connections will form between cells that represent different memories. This enables brain structures that have slow NMDA channels to store heteroassociative sequence information in long-term memory. Recall of this stored sequence information can be initiated by presentation of initial elements of the sequence. The remaining sequence is then recalled at a rate of one memory every gamma cycle. A new role for the NMDA channel suggested by our finding is that recall at gamma frequency works well if slow NMDA channels provide the dominant component of the EPSP at the synapse of recurrent collaterals: The slow onset of these channels and their long duration allows the firing of one memory during one gamma cycle to trigger the next memory during the subsequent gamma cycle. An interesting feature of the readout mechanism is that the activation of a given memory is due to cumulative input from multiple previous memories in the stored sequence, not just the previous one. The network thus stores sequence information in a doubly redundant way: Activation of a memory depends on the strength of synaptic inputs from multiple cells of multiple previous memories. The cumulative property of sequence storage has support from the psychophysical literature. Cumulative learning also provides a solution to the disambiguation problem that occurs when different sequences have a region of overlap. In a final set of simulations, we show how coupling an autoassociative network to a heteroassociative network allows the storage of episodic memories (a unique sequence of briefly occurring known items). The autoassociative network (cortex) captures the sequence in short-term memory and provides the accurate, time-compressed repetition required to drive synaptic modification in the heteroassociative network (hippocampus). This is the first mechanistically detailed model showing how known brain properties, including network oscillations, recurrent collaterals, AMPA channels, NMDA channel subtypes, the ADP, and the AHP can act together to accomplish memory storage and recall.

Association Learning↗

PubMed1994

Subjective memory complaints and personality traits in normal elderly subjects.

OBJECTIVE: To evaluate the relationship between objectively measured memory functions and subjective complaints of memory disturbance and whether subjective complaints are affected by some personality traits or affective states. DESIGN: Cross-sectional two-group comparison. SETTING: The city of Kuopio in Eastern Finland, considered representative of the urban elderly population of Finland. PARTICIPANTS: Originally 403 subjects aged 67-78 years from the random sample and then two matched study groups initially including eighteen subjects but only ten in the final analysis. MEASUREMENTS: Screening and follow-up examinations of subjects with and without subjective memory complaints: (1) Memory functions: Benton's visual retention test and the paired-associated learning subtest of Wechsler Memory Scale. (2) Memory complaints: Memory Complaint Questionnaire. (3) Personality traits and affective state: Two subscales from Minnesota Multiphasic Personality Inventory and Geriatric Depression Scale. RESULTS: Complaints of memory loss did not correlate with the actual memory performance in the tests. However, those subjects who most emphatically complained of memory disturbance had greater tendencies toward somatic complaining, higher feelings of anxiety about their physical health, and more negative feelings of their own competence and capabilities than those who did not complain of memory deterioration associated with aging. CONCLUSIONS: The study suggests that subjective feelings of memory impairment are more closely associated with personality traits than with actual memory performance in normal elderly people.

Affect↗

PubMed1991

Effects of morphine on memory: interactions with naloxone, propranolol and haloperidol.

The effects of morphine on memory have been shown to be dependent on the strain of animal used and on the experimental parameters. Memory was assessed in a passive avoidance task using Swiss albino (ICRC) mice. Morphine at doses of 1, 3 and 10 mg kg-1 was administered immediately after foot shock (memory retention) or 23.5 h after foot shock (memory retrieval). Retest step-down latencies measured 24 h later showed that morphine did not affect memory retention but dose-dependently impaired retrieval of memory. Administration of naloxone 0.1 mg kg-1 antagonised the effects of morphine and impaired memory retention. Propranolol 0.3 mg kg-1 along with morphine 3 mg kg-1 impaired memory retention only while haloperidol 0.1 mg kg-1 improved the impairment of memory retrieval caused by morphine 3 mg kg-1. Glucose did not alter the effects of morphine on memory. There was no per se effect of morphine, naloxone, propranolol, glucose and haloperidol on memory at the doses used. The effect of morphine on memory retention is mediated by opioid mechanisms; however, adrenergic and dopaminergic mechanisms possibly modulate retention and retrieval of memory, respectively.

Animals↗

PubMed1995

Remembering the past: two facets of episodic memory explored with positron emission tomography.

OBJECTIVE: This study used positron emission tomography to examine two kinds of personal memory that are used in psychiatric evaluation: focused episodic memory (recall of past experience, employed in "taking a history") and random episodic memory (uncensored thinking about experience, examined during analytic therapy using free association). For comparison, a third memory task was used to tap impersonal memory that represents general information about the world ("semantic memory"). METHOD: Thirteen subjects were studied using the [15O]H2O method to obtain quantitative measurements of cerebral blood flow. The three conditions were subtracted and their relative relationships examined. RESULTS: The random episodic condition produced activations in widely distributed association cortex (right and left frontal, parietal, angular/supramarginal, and posterior inferior temporal regions). Focused episodic memory engaged a network that included the medial inferior frontal regions, precuneus/retrosplenial cingulate, anterior cingulate, thalamus, and cerebellum. The use of medial frontal regions and the precuneus/retrosplenial cingulate was common to both focused and random episodic memory. The major difference between semantic and episodic memory was activation of Broca's area and the left frontal operculum by semantic memory. CONCLUSIONS: These results indicate that free-ranging mental activity (random episodic memory) produces large activations in association cortex and may reflect both active retrieval of past experiences and planning of future experiences. Focused episodic memory shares some components of this circuit (inferior frontal and precuneus), which may reflect the time-linked components of both aspects of episodic memory, and which permit human beings to experience personal identity, consciousness, and self-awareness.

Adult↗

PubMed1996

Neural mechanisms in dissociative amnesia for childhood abuse: relevance to the current controversy surrounding the "false memory syndrome".

OBJECTIVE: There is considerable controversy about delayed recall of childhood abuse. Some authors have claimed that there is a "false memory syndrome," in which therapists suggest to patients events that never actually occurred. These authors point to findings that suggest that memory traces are susceptible to modification. The purpose of this paper is to review the literature on the potential vulnerability of memory traces to modification and on the effects of stress on the neurobiology of memory. METHOD: The authors review findings on mechanisms involved in normal memory function, effects of stress on memory in normal persons, children's memory of stressful events, and alterations of memory function in psychiatric disorders. The effects of stress on specific brain regions and brain chemistry are also examined. RESULTS: Neuropeptides and neurotransmitters released during stress can modulate memory function, acting at the level of the hippocampus, amygdala, and other brain regions involved in memory. Such release may interfere with the laying down of memory traces for incidents of childhood abuse. Also, childhood abuse may result in long-term alterations in the function of these neuromodulators. CONCLUSIONS: John Nemiah pointed out several years ago that alterations in memory in the form of dissociative amnesia are an important part of exposure to traumatic stressors, such as childhood abuse. The studies reviewed here show that extreme stress has long-term effects on memory. These findings may provide a model for understanding the mechanisms involved in dissociative amnesia, as well as a rationale for phenomena such as delayed recall of childhood abuse.

Amnesia↗

PubMed2004

Intracarotid Amytal memory test and hippocampal magnetic resonance imaging volumetry: validity of the Wada test as an indicator of hippocampal integrity among candidates for epilepsy surgery.

OBJECT: Intracarotid Amytal testing (the Wada test) has been used to lateralize language and identify patients who may be at risk for memory impairment after temporal lobectomy. The goal of this study was to determine the validity of the Wada test in the assessment of pathological conditions of the hippocampus among candidates for epilepsy surgery. The authors examined the correlation between the functional integrity of the hippocampus, measured using the Wada test, and quantitative measures of hippocampal pathology, determined by obtaining volumetric measurements of the hippocampus with the aid of magnetic resonance (MR) imaging. METHODS: The authors reviewed the relationship between memory scores on the Wada test and hippocampal volumes measured on preoperative MR images in 76 patients who underwent anteromedial temporal lobectomy and amygdalohippocampectomy for the treatment of medically refractory temporal lobe epilepsy. The data were analyzed with respect to their usefulness in lateralizing the seizure focus and predicting the long-term postoperative memory outcome. Right and left hippocampal volume measurements did not correlate with one another (p > 0.1). Similarly, following a left carotid artery injection of Amytal the patients' right hemisphere memory was not significantly related to their left hemisphere memory on the Wada test (p'> 0.1). On the other hand, the patients' right hemisphere memory significantly correlated with their right hippocampal volume (r = 0.51; p < 0.001) and their left hemisphere memory significantly correlated with their left hippocampal volume (r = 0.51; p < 0.001). Both right and left hemisphere memory scores correlated with the hippocampal volumetry ratio (r = 0.47 and r = 0.45, respectively; both p < 0.001). Lateralization of a seizure focus based on hippocampal volumetry results was significantly related to lateralization based on the results of the Wada test (r = 0.49; p < 0.01). The disparity between the Wada memory scores on ipsilateral and contralateral sides was significantly and inversely related to the change in verbal memory following temporal lobectomy (r = -0.28; p < 0.02). The preoperative hippocampal volumetry ratio also significantly and inversely correlated with the change in verbal memory after surgery (r = -0.31; p < 0.01). CONCLUSIONS: The Wada memory test may be a valuable method of measuring the functional integrity of the hippocampus. The systematic study of MR imaging-acquired morphological data and Wada-acquired neuropsychological data may increase our understanding of the location of material-specific memory and the selection of eligible candidates for epilepsy surgery.

Adolescent↗

PubMed2005

Modulation of memory CD4 T cell function and survival potential by altering the strength of the recall stimulus.

Optimization of long term immunity depends on the functional persistence of memory T cells; however, there are no defined strategies for promoting memory T cell function and survival. In this study, we hypothesized that varying the strength of the recall stimulus could modulate the function and survival potential of memory CD4 T cells. We tested the ability of peptide variants of influenza hemagglutinin (HA) exhibiting strong and weak avidity for an HA-specific TCR, to modulate HA-specific memory CD4 T cells in vitro and in vivo. In vitro stimulation with a weak avidity peptide (L115) uncoupled memory CD4 T proliferation from effector cytokine production with low apoptosis, whereas stimulation with a strong avidity peptide (Y117) fully recalled memory T cell functions but triggered increased apoptosis. To determine how differential recall would affect memory T cells in vivo, we boosted BALB/c hosts of transferred, CFSE-labeled HA-specific memory CD4 T cells with native HA, Y117, and L115 variant peptides and found differences in early Ag-driven memory T cell proliferation and IL-7R expression, with subsequent changes in memory T cell yield. High avidity boosting resulted in rapid proliferation, extensive IL-7R down-regulation, and the lowest yield of HA-specific memory cells, whereas low avidity boosting triggered low in vivo proliferation, maintenance of IL-7R expression, and the highest memory T cell yield. Our results indicate that memory CD4 T cell function and survival can be modulated at the recall level, and can be optimized by low level stimulation that minimizes apoptosis and enhances responses to survival factors.

Animals↗

PubMed2006

Effector T cell differentiation and memory T cell maintenance outside secondary lymphoid organs.

Naive T cell circulation is restricted to secondary lymphoid organs. Effector and memory T cells, in contrast, acquire the ability to migrate to nonlymphoid tissues. In this study we examined whether nonlymphoid tissues contribute to the differentiation of effector T cells to memory cells and the long-term maintenance of memory T cells. We found that CD4, but not CD8, effector T cell differentiation to memory cells is impaired in adoptive hosts that lack secondary lymphoid organs. In contrast, established CD4 and CD8 memory T cells underwent basal homeostatic proliferation in the liver, lungs, and bone marrow, were maintained long-term, and functioned in the absence of secondary lymphoid organs. CD8 memory T cells found in nonlymphoid tissues expressed both central and effector memory phenotypes, whereas CD4 memory T cells displayed predominantly an effector memory phenotype. These findings indicate that secondary lymphoid organs are not necessary for the maintenance and function of memory T cell populations, whereas the optimal differentiation of CD4 effectors to memory T cells is dependent on these organs. The ability of memory T cells to persist and respond to foreign Ag independently of secondary lymphoid tissues supports the existence of nonlymphoid memory T cell pools that provide essential immune surveillance in the periphery.

Animals↗

PubMed1999

Induction and visualization of mucosal memory CD8 T cells following systemic virus infection.

Whether CD8 T cell memory exists outside secondary lymphoid organs is unclear. Using an adoptive transfer system that enables tracking of OVA-specific CD8 T cells, we explored the antigenic requirements for inducing CD8 T cell memory and identified intestinal mucosa memory cells. Although systemic immunization with soluble OVA induced clonal expansion, memory CD8 cells were not produced. In contrast, infection with virus-encoding OVA induced memory CD8 cells in the periphery and the lamina propria and intraepithelial compartments of the intestinal mucosa. Mucosal memory cells expressed a distinct array of adhesion molecules as compared with secondary lymphoid memory cells, suggesting that there may be separate mucosal and systemic memory pools. Mucosal CD8 memory cells rapidly produced IFN-gamma after Ag stimulation. Reactivation of memory cells by Ag feeding resulted in increased cell size and up-regulation of CD28 and CD11c. CD8 mucosal memory cells exhibited ex vivo lytic activity that was up-regulated dramatically following Ag reencounter in vivo. Interestingly, reactivation of memory cells did not require CD28-mediated costimulation. The ability of the intestinal mucosa to maintain CD8 memory cells provides a potential mechanism for effective mucosal vaccination.

Animals↗

PubMed1999

[Everyday memory impairment in Parkinson's disease].

Memory impairment has been frequently reported in patients with Parkinson's disease. The traditional tests used in previous studies, however, failed to sufficiently reflect memory performance in everyday life. To investigate everyday memory in patients with Parkinson's disease, an objective test of everyday memory, the Rivermead Behavioural Memory Test (RBMT), and an everyday memory questionnaire were administered to 26 parkinsonian patients and 26 age-matched normal controls. The parkinsonian patients scored significantly lower on the RBMT than the controls (p < 0.01). Moreover, the parkinsonian patients performed especially poorly on subtests related to prospective memory (p < 0.05). These subtests are thought to be sensitive to frontal lobe function. On the everyday memory questionnaire, the parkinsonian patients estimated their own everyday memory to be significantly worse than did the controls (p < 0.01). Further, the patients estimated their everyday memory to be especially poor in comparison with the controls on the sub-items related to recency memory (p < 0.05), source memory (p < 0.01), action slip (p < 0.01), and tip-of-the-tongue phenomenon (p < 0.05). In the patient group, the RBMT score correlated significantly with the scores on the Wisconsin Card Sorting Test (p < 0.05) and tests of verbal fluency (p < 0.05). These results indicate that everyday memory is impaired in patients with Parkinson's disease, and that this impairment is partly related to frontal lobe dysfunction.

Aged↗

PubMedDate not supplied

[The psychobiology of learning and memory: fundamentals and recent advances].

AIM: This review describes the concepts, temporal dynamics and main features of learning and memory systems from a comprehensive molecular, neuroanatomical, neurophysiological, cognitive and behavioural approach. DEVELOPMENT: Starting with molecular mechanisms of synaptic plasticity we describe the memory stages, implicit and explicit memory systems, working memory, remembering and forgetting. Each process is illustrated with examples of recent experimental and clinical research. CONCLUSIONS: Learning and memory are closely related brain processes which give rise to adaptive changes in behaviour. Implicit memory is a kind of unconscious and rigid memory for habits, which is based on brain regions processing perceptions and motor and emotional information, like the neocortex, the neostriatum, the cerebellum or the amygdala. Explicit or declarative memory is a conscious and flexible memory, hippocampus-dependent. Working memory is actually a system of executive cognition, based on interactions between the prefrontal cortex and other brain regions. The retrieval of complex memories consist of an active process of reconstruction of the past which incorporates new experiences of the subject who is remembering. The reactivation of memories can initiate genuine processes of reconsolidation and extinction. Forgetting could depend on alterations in the neural networks storing the information or, otherwise, on active processes which hinder consolidation or block the expression of the memories.

Animals↗