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PubMed1989

Role of ACTH in recovery from retrograde amnesia induced by hypothermia in rats.

The present investigation assessed whether increased congruency between ACTH state present shortly after training and that at testing contributed to memory recovery. If recovery were related to an increased correspondence between internal state present after training and that at testing, then suppressing ACTH release should block memory recovery. This was the hypothesis that was examined in the present investigation. Specifically, animals were trained on a passive avoidance task, administered hypothermia (the amnestic agent) and, shortly prior to testing, given treatments known to be effective in reversing memory loss induced by hypothermia. Before training (Experiment 1) or testing (Experiment 2) animals were injected with either dexamethasone (an agent that suppresses ACTH release) or saline. Results, in general, indicated that when ACTH release was suppressed, a blunted recovery effect was obtained. This reduction in the extent of memory recovery was observed when ACTH was suppressed either at training or at testing. These data are interpreted as providing support for an ACTH-related, state-dependent retention mechanism contributing to recovery from hypothermia-induced retrograde amnesia in rats.

Adrenocorticotropic Hormone↗

PubMed1994

Ontogeny of contextual fear conditioning in rats: implications for consolidation, infantile amnesia, and hippocampal system function.

The authors present developmental evidence that contextual fear conditioning is supported by a short-term memory system that supports conditioning immediately after a shock and by a long-term memory system that supports contextual conditioning 24 hr after training. This is based on the finding that after 1 conditioning trial, rats 18 to 32 days old show the same amount of conditioned freezing when tested immediately after conditioning but 18-day-old rats show much less conditioned freezing than the older rats when the retention interval is 24 hr. The data also suggest that the long-term memory representation of context that mediates conditioned fear is not available until several hours after the conditioning trial. Implications of these findings for memory consolidation processes, infantile amnesia, and hippocampal formation development are discussed.

Aging↗

PubMed1994

Midazolam administered to rats induces anterograde amnesia for changes in reward magnitude.

L. P. Crespi (1942) showed that rats trained to run an alley for a large food reward slowed down when shifted to a small reward. This effect is usually interpreted as an aversive emotional response to reward reduction (A. Amsel, 1958). Benzodiazepines attenuate the behavioral effects of reward reduction (cf. C. F. Flaherty, 1990), but the emphasis has been on their anxiolytic, not memory-impairing, effects. Researchers trained rats (175-200 g) to run an alley for food until asymptote was reached. Reward magnitude was then either decreased (Experiment 1) or increased (Experiment 2). The benzodiazepine midazolam (1 mg/kg ip), injected immediately prior to a decrease or increase in reward magnitude, impaired the later retention of both changes in a manner consistent with anterograde amnesia. The findings suggest that the memory-impairing effects of benzodiazepines may, at least in part, influence the response to reward reduction.

Animals↗

PubMed1993

Novelty monitoring, metacognition, and control in a composite holographic associative recall model: implications for Korsakoff amnesia.

This article stems from a technical problem in composite-trace distributed models of human memory and particularly in the Composite Holographic Associative Recall Memory (CHARM) model. Briefly, the composite trace--used as a central construct in such models--can become catastrophically out of control. To solve the problem, a prestorage novelty-familiarity monitor and a simple control procedure need to be implemented. Eight lines of experimental evidence converge on the idea that output from such a novelty-familiarity monitor underlies people's metacognitive judgments of feeling of knowing. Breakdown of the monitoring-control mechanism produces Korsakoff-like symptoms in the model. Impairments in feeling-of-knowing judgments and the failure to release from proactive inhibition, both characteristic of Korsakoff amnesia, are thus attributed to a monitoring-control failure rather than to deficits in the basic memory system.

Alcohol Amnestic Disorder↗

PubMed2003

Anterograde amnesia for Pavlovian fear conditioning and the role of one-trial overshadowing: effects of preconditioning exposures to morphine in the rat.

Four experiments studied anterograde deficits in Pavlovian fear conditioning following prolonged exposure to the mu-opioid receptor agonist morphine. Injections of morphine produced temporally graded anterograde amnesia characterized by deficits in contextual and conditioned-stimulus (CS) conditioning 1 or 7 days and selective impairment in CS conditioning 21 days after last injection. This anterograde deficit in conditioning did not recover across a retention interval, was absent when rats were tested immediately after conditioning, and required the presence of an auditory CS. These results suggest that anterograde deficits in Pavlovian fear conditioning emerged from differences in susceptibility to 1-trial overshadowing of context by CS.

Acoustic Stimulation↗

PubMed1980

Disruption of conditioned taste aversion in the rat by stimulation of amygdale: a conditioning effect, not amnesia.

Two experiments were conducted to determine whether the disruption of conditioned taste aversion by delivery of amygdaloid brain stimulation during conditioning could be attributed to the stimulus properties of the brain stimulation. In Experiment 1, animals receiving brain stimulation (a) while drinking saccharin, (b) during the onset of LiCl toxicosis, or (c) in the interval between taste exposure and toxicosis drank significantly more saccharin solution during a 48 hr retest than implanted or unoperated controls receiving similar taste-toxicosis pairings. In contrast, a group receiving brain stimulation during both conditioning and retention trials developed a strong conditioned aversion. Experiment 2 confirmed that amygdaloid stimulation can form a compound with the taste of the saccharin solution. A small but significant aversion was displayed by groups exposed to brain stimulation plus taste during conditioning and to either taste alone or brain stimulation alone during the retest. Again, the group presented with brain stimulation and taste prior to and following LiCl toxicosis displayed a strong conditioned aversion. These data suggest that disruption of conditioned taste aversion with amygdaloid stimulation represents a conditioning effect, not amnesia.

Amygdala↗

PubMed1981

Differential effects of a reminder cue on amnesia induced by stimulation of amygdala and hippocampus.

The present study examined the effects of a footshock reminder in restoring memory after discrete electrical brain stimulation. Rats received low-level bilateral electrical stimulation of either the amygdala or the hippocampus after training in a one-trial passive avoidance task. Rats receiving stimulation showed amnesia when tested 24 hr after training. One hour after the retention test, rats received a footshock reminder cue. Twenty-three hours later, in a second retention test, hippocampus-stimulated animals showed recovery of memory, while amygdala-stimulated rats did not. Stimulated rats that did not receive a reminder footshock remained amnesic. In addition, the effects of amygdala and hippocampal stimulation applied after the footshock reminder cue were examined. On the second retention test, amygdala stimulation disrupted the reminder effect, while hippocampal stimulation had no deleterious effects. The data are interpreted from a memory-attribute point of view which suggests that the amygdala and hippocampus may be differentially involved in the processing of particular attributes of the learning task.

Amygdala↗

PubMed1988

Relation of sedation and amnesia to plasma concentrations of midazolam in surgical patients.

The kinetics and dynamics of midazolam were investigated in 20 female patients undergoing lower abdominal surgery. The relation between the plasma concentrations of midazolam and pharmacokinetic end points was evaluated after an intravenous infusion regimen in 10 patients given an epidural anesthetic. The remaining 10 patients were anesthetized with a totally intravenous anesthetic technique with midazolam and alfentanil. The effect was assessed by means of a rating scale divided into degree of sedation and amnesia. A good correlation was found between plasma level of midazolam and pharmacodynamic response. The relation between the quantal response data and the plasma concentration was represented by an s-shaped concentration-effect curve. Despite similar kinetics of midazolam in the two groups, the postoperative drowsiness was more pronounced in the group receiving total intravenous anesthesia. The concomitant administration of alfentanil shifted the concentration-effect curve regarding sedation to the left.

Adult↗

PubMed2003

Turning immunological memory into amnesia by depletion of dividing T cells.

Immunological memory, defined as more efficient immune responses on antigen reexposure, can last for decades. The current paradigm is that memory is maintained by antigen-experienced "memory T cells" that can be long-lived quiescent or dividing. The contribution of T cell division to memory maintenance is poorly known and has important clinical implications. In this study, we directly addressed the role of dividing T cells in immunological memory maintenance by evaluating the consequences of their elimination. The specific ablation of dividing T cells was obtained by administration of ganciclovir to immune mice expressing the herpes simplex type 1 thymidine kinase suicide gene in T cells. We show that depletion of dividing T cells for 5 or 2 weeks suffices to abolish in vitro and in vivo memory responses against the male H-Y transplantation alloantigen or against lymphocytic choriomeningitis virus antigens, respectively. Similar results were obtained after the nonspecific elimination of all dividing cells by using hydroxyurea, a cytostatic toxic agent commonly used for cancer chemotherapy. This immune amnesia occurred in otherwise immunocompetent mice and despite the persistence of functional quiescent T cells displaying a "memory" phenotype. Thus, division of antigen-experienced T cells is an absolute requirement for immunological memory maintenance and the current concept of memory T cells is challenged.

Animals↗

PubMed2002

Johann August Philipp Gesner (1738-1801). A review of his essay "The language amnesia" in the bicentennial anniversary of his death.

On the 200th anniversary of Johann August Philipp Gesner's death, this paper summarizes and discusses a paper on language amnesia published in 1770. The author had clear knowledge of selective mental impairments resulting from brain diseases, and of separate mental representations for words and their underlying concepts. However, to explain the language impairment, Gesner suggested that it would not be caused by focal damage to a specific anatomic and functional unit of the mind, but is the consequence of a general sluggishness of the mental processes.

Aphasia↗

PubMed2000

The impact of posthypnotic amnesia and directed forgetting on implicit and explicit memory: new insights from a modified process dissociation procedure.

The authors describe a study investigating the relationship between posthypnotic amnesia (PHA) and directed forgetting (DF) and their impact on implicit and explicit memory. This study adopted a recent modification of the process dissociation procedure to accommodate the cross-contamination of memory test performance by implicit and explicit memorial factors. Forty high and 40 low hypnotically susceptible participants were compared in PHA, DF, and control conditions on estimates of voluntary conscious (VCM), involuntary conscious (ICM), and involuntary unconscious memory (IUM) performance. Both groups showed significant decrements in VCM and ICM following instructions for DF, whereas only high susceptibles showed this decrement in the PHA condition; neither DF nor PHA affected IUM. Moreover, there was no relationship between forgetting in PHA and DF. Although both PHA and DF seem to prevent the conscious (i.e., explicit) expression of memorial information while leaving implicit memory intact, the mechanisms underlying these phenomena may nevertheless be different.

Adult↗

PubMed1989

Disturbed memory and amnesia related to intensive care.

Patients, when admitted to an intensive care unit (ICU), have one thing in common: their illness is life-threatening. Patients may remain on ICU in a critical condition, needing support with their breathing, circulation, and/or kidneys for varying lengths of time, from days to weeks. During that time the patients will receive sedative and analgesic drugs to ensure compliance with artificial ventilation. Patients recovering from critical illness frequently have little or no recall of their period in ICU, or remember nightmare, hallucinations, or paranoid delusions. The nature, extent and reason for these difficulties, have been under-reported and consequently our purpose was to conduct a review of memory problems experienced by ICU patients. A systematic literature review of computer databases (Medline, PsycLit, and CINAHL) identified 25 relevant papers. In addition, other relevant articles were obtained, citation lists and associated articles retrieved. Due to lack of research on processes underlying memory problems in ICU patients all articles that introduced an insight into possible mechanisms were included in the review. There seem to be two possible processes contributing to memory problems in ICU patients. First the illness and treatment may have a general dampening effect on memory. Delirium and sleep disturbance are both common in ICU patients. Delirium can result in a profound amnesia for the period of confusion. Sleep deprivation exacerbates the confusional state. Slow wave sleep is important for the consolidation of episodic memories. Treatment administered to patients in ICU can have effects on memory. Opiates, benzodiazepines, sedative drugs such as propofol, adrenaline, and corticosteroids can all influence memory. In addition, the withdrawal of drugs, such as benzodiazepines, can cause profound withdrawal reactions, which may contribute to delirium. Second, we hypothesise that there is a process that affects memory negatively for external events but enhances memory for internal events. The physical constraints and social isolation experienced by ICU patients and the life-threatening nature of the illness may increase the experience of hypnagogic hallucinations. Attentional shift during hypnagogic images from external stimuli to internally generated images would explain why ICU patients have such poor recall of external ICU events, but can clearly remember hallucinations and nightmares. Patients describe these memories as being very vivid and this is explored in terms of flashbulb memory formation. The absence of memories for real events on ICU can result in ICU patients remembering paranoid delusions of staff trying to kill them, with little information to reject these vivid memories as unreal. This has implications for patients' future psychological health.

Critical Care↗

PubMed1994

Very long-term recall in infants: infantile amnesia reconsidered.

Subjects who had participated in a study on non-verbal recall before their first birthday returned to the laboratory one year later and were tested for recall of their previous visit. During their previous visit they had shown recall of both familiar and novel actions on a set of novel objects. However, after a year's delay, evidence for recall was found for the familiar actions only. One action in particular was responsible for this finding: feeding a teddy bear with a schematic bottle. The majority of the returning subjects who had been shown this action repeated it after a year, whereas none of the other returning subjects and few of the subjects in the control groups performed this action. The results indicate that young infants have the ability to recall an event both at 11 months of age and after a delay as long as one year. The finding that infants can recall during a period that later becomes inaccessible to memory is important to our understanding of infantile amnesia.

Analysis of Variance↗

PubMed1999

Childhood amnesia: on answering questions about very early life events.

Twenty five young adults were asked about the events surrounding the birth of a younger sibling which took place when they were under the age of 2 years. Approximately 40% of the participants claimed to have significant memories of the events. The mothers of our participants verified that a majority of their answers were accurate. Comparing the pattern of data with those previously collected (Eacott & Crawley, 1998) suggests that the memories of those who were aged below 2:0 are qualitatively similar to the memories of those who were older at the time of events and dissimilar in type to those who are basing their reports on reconstructions from family knowledge. This finding may be evidence that memories of events that occurred before the age of 2 years are genuine but rare. This conclusion may be useful in assessing theories of childhood amnesia.

Adult↗

PubMed2004

"Functional motor amnesia" in stroke (1904) and "learned non-use phenomenon" (1966).

The "learned non-use phenomenon" described by Taub, one of the most original recent contributions to rehabilitation medicine probably corresponds to what Henry Meige (1866-1940), who studied under J.-M. Charcot, described in hemiplegics in 1904 using the expression "functional motor amnesia". He specified in 1914 at the time of the Babinski description of anosognosia, that: "Even with educated subjects who are still relatively young we are sometimes confronted with strange incapacities that are not due to impotence, negligence, or lack of confidence in the results. [...] With the transitory halting of the motility all memory of the function appears to have disappeared". Meige describes motor disorders that are: (i) distinct from lesional paralyses; (ii) secondary to the absence of activity; (iii) linked to a learning process; (iv) linked to a phenomenon of functional memory loss; (v) reversible; and (vi) motor re-education focusing on extended and repeated practice of the lost function: the same characteristics as the "phenomenon of learned non-use" described by Taub in monkeys then in man.

France↗

PubMed2004

'In the course of time': a PET study of the cerebral substrates of autobiographical amnesia in Alzheimer's disease.

Neuroimaging studies in healthy subjects have yielded controversial results about the neural substrates of autobiographical memory. Moreover, the neural networks responsible for autobiographical amnesia remain poorly understood. Since autobiographical memory is frequently altered in Alzheimer's disease (AD), we used this degenerative disorder as a model and applied a correlative approach between resting cerebral glucose utilization (CMRGlc) and temporally graded memory scores to identify the cerebral structures whose synaptic dysfunction subserves the impairment in autobiographical memory. To this end, we studied a group of 17 AD patients with mild to moderate dementia in whom autobiographical memory was assessed using a specially designed task from three broad time periods [the previous 5 years (period A); middle age (period B); and teenage and childhood (period C)], and measures of resting CMRGlc were obtained with PET. The patients performed less well than a control group for all three time periods and showed the expected temporal gradient, with the most remote period being best preserved (Ribot's gradient). Qualitative analysis showed that remote memories concerned generic (i.e. semantic) rather than specific (i.e. episodic) events. We found a significant positive correlation between autobiographical scores and the metabolism of the right hippocampus (extending to the lingual gyrus), restricted to period A. In addition, period A scores were significantly correlated with the right middle and inferior frontal gyri and the right middle temporal gyrus. Period B scores correlated chiefly with the prefrontal cortex bilaterally (bilateral superior, bilateral middle and right inferior gyri). Metabolic correlations with period C scores were restricted to the left middle frontal gyrus. These findings show striking differences in metabolic correlations with the autobiographical time period, in agreement with prevalent theories of normal functioning of human memory. Thus, in accordance with theories of long-term memory consolidation, we find the expected implication of the hippocampal region in the recall of recent memories, and a disengagement of this structure when the retention interval is beyond 5 years. Moreover, according to the hemispheric encoding/retrieval asymmetry model based on activation studies in healthy subjects, the fact that recent memories preferentially involved the right prefrontal cortex whereas remote memories involved the left prefrontal cortex supports the notion of semanticization of memories with time interval, such that preserved remote memories in AD have a predominantly semantic character.

Aged↗

PubMed1992

Amnesia for Complex Naturalistic Scenes and for Objects Following Fornix Transection in the Rhesus Monkey.

Rhesus monkeys (Macaca mulatta) were trained to discriminate among many complex naturalistic scenes. The scenes were still frames from a cinema film. They were presented as the discriminative stimuli in a concurrent discrimination learning task in which each discriminative stimulus was presented on one trial each day. Learning of this task was severely impaired by fornix transection. The same animals were also deficient in a similar concurrent discrimination learning task, with each discriminative stimulus presented on one trial each day, but with objects, not complex scenes, as the stimulus material. The impairment in object discrimination learning in the present experiment is attributable to an interaction of object discrimination learning with scene discrimination learning, and can be understood as an effect of interference in long-term memory. In contrast to these impairments in long-term memory, a test of within-session learning of complex scenes, in which the average interval between successive presentations of the same stimulus was < 3 min, was performed without significant impairment by the fornix-transected animals. These results show that long-term memory for complex naturalistic scenes reveals analogues in the monkey of human episodic memory and its impairment in amnesia.

Journal Article↗