Amnesia Memory Research Articles

Temporary amnesia from sleep loss: A framework for understanding consequences of sleep deprivation.

Throughout its modern history, sleep research has been concerned with both the benefits of sleep and the deleterious impact of sleep disruption for cognition, behavior, and performance. When more specifically examining the impact of sleep on memory and learning, however, research has overwhelmingly focused on how sleep following learning facilitates memory, with less attention paid to how lack of sleep prior to learning can disrupt subsequent memory. Although this imbalance in research emphasis is being more frequently addressed by current investigators, there is a need for a more organized approach to examining the effect of sleep deprivation before learning. The present review briefly describes the generally accepted approach to analyzing effects of sleep deprivation on subsequent memory and learning by means of its effects on encoding. Then, we suggest an alternative framework with which to understand sleep loss and memory in terms of temporary amnesia from sleep loss (TASL). The review covers the well-characterized properties of amnesia arising from medial temporal lobe lesions and shows how the pattern of preserved and impaired aspects of memory in amnesia may also be appearing during sleep loss. The view of the TASL framework is that amnesia and the amnesia-like deficits observed during sleep deprivation not only affect memory processes but will also be apparent in cognitive processes that rely on those memory processes, such as decision-making. Adoption of the TASL framework encourages movement away from traditional explanations based on narrowly defined domains of memory functioning, such as encoding, and taking instead a more expansive view of how brain structures that support memory, such as the hippocampus, interact with higher structures, such as the prefrontal cortex, to produce complex cognition and behavioral performance, and how this interaction may be compromised by sleep disruption.

Possession Amnesia

Abstract The occurrence of possession amnesia—memory loss subsequent to the cessation of possession by a spirit—is chronicled in Akkadian, Greek, early Jewish, and Christian literature. Anthropologists have collected data that witness to the same phenomenon occurring in indigenous cultures. Anthropologists have argued that patterns of experience with certain inexplicable phenomena, such as with spirits, may provide clues for evidence of their existence. This article discusses patterns of possession amnesia that occur cross-culturally and transhistorically as possible evidential support for the existence of spirits.

Italian Cinema and the Fascist Past: Tracing Memory Amnesia

In Italy, cinema has contributed to constructing a paradox of memory in which the rememberer is asked to prevent past mistakes from happening again and yet is encouraged to forget what those mistakes were, or that they ever even took place. Through an examination of the long-term trends in Italian cinema about the Fascist period, this article explores its recurrent tropes alongside its recurrent absences, isolating in particular the act of killing and Italy’s African Empire as crucial absences in Italy’s memory. The dominant narrative of italiani brava gente explains popular amnesia and institutional silences that still surround the darkest and bloodiest pages in Italy’s history. From the narratives of innocence and sacrifice that populate the canon of Italian film about Fascism to the sanitised representations of Italy’s wars of aggression or the boycott of Moustapha Akkad’s The Lion of the Desert (1981), this paper argues that recurrent presences and absences in Italy’s cinematic memories of the long Second World War have not been random but coherent, cogent and consistent.

Short-term retention of relational memory in amnesia revisited: accurate performance depends on hippocampal integrity

Traditionally, it has been proposed that the hippocampus and adjacent medial temporal lobe cortical structures are selectively critical for long-term declarative memory, which entails memory for inter-item and item-context relationships. Whether the hippocampus might also contribute to short-term retention of relational memory representations has remained controversial. In two experiments, we revisit this question by testing memory for relationships among items embedded in scenes using a standard working memory trial structure in which a sample stimulus is followed by a brief delay and the corresponding test stimulus. In each experimental block, eight trials using different exemplars of the same scene were presented. The exemplars contained the same items but with different spatial relationships among them. By repeating the pictures across trials, any potential contributions of item or scene memory to performance were minimized, and relational memory could be assessed more directly than has been done previously. When test displays were presented, participants indicated whether any of the item-location relationships had changed. Then, regardless of their responses (and whether any item did change its location), participants indicated on a forced-choice test, which item might have moved, guessing if necessary. Amnesic patients were impaired on the change detection test, and were frequently unable to specify the change after having reported correctly that a change had taken place. Comparison participants, by contrast, frequently identified the change even when they failed to report the mismatch, an outcome that speaks to the sensitivity of the change specification measure. These results confirm past reports of hippocampal contributions to short-term retention of relational memory representations, and suggest that the role of the hippocampus in memory has more to do with relational memory requirements than the length of a retention interval.

Self-referential processing is distinct from semantic elaboration: Evidence from long-term memory effects in a patient with amnesia and semantic impairments

We report data demonstrating that self-referential encoding facilitates memory performance in the absence of effects of semantic elaboration in a severely amnesic patient also suffering semantic problems. In Part 1, the patient, GA, was trained to associate items with the self or a familiar other during the encoding phase of a memory task (self-ownership decisions in Experiment 1 and self-evaluation decisions in Experiment 2). Tests of memory showed a consistent self-reference advantage, relative to a condition where the reference was another person in both experiments. The pattern of the self-reference advantage was similar to that in healthy controls. In Part 2 we demonstrate that GA showed minimal effects of semantic elaboration on memory for items he semantically classified, compared with items subject to physical size decisions; in contrast, healthy controls demonstrated enhanced memory performance after semantic relative to physical encoding. The results indicate that self-referential encoding, not semantic elaboration, improves memory in amnesia. Self-referential processing may provide a unique scaffold to help improve learning in amnesic cases.

Intact Memory for Irrelevant Information Impairs Perception in Amnesia

SummaryMemory and perception have long been considered separate cognitive processes, and amnesia resulting from medial temporal lobe (MTL) damage is thought to reflect damage to a dedicated memory system. Recent work has questioned these views, suggesting that amnesia can result from impoverished perceptual representations in the MTL, causing an increased susceptibility to interference. Using a perceptual matching task for which fMRI implicated a specific MTL structure, the perirhinal cortex, we show that amnesics with MTL damage including the perirhinal cortex, but not those with damage limited to the hippocampus, were vulnerable to object-based perceptual interference. Importantly, when we controlled such interference, their performance recovered to normal levels. These findings challenge prevailing conceptions of amnesia, suggesting that effects of damage to specific MTL regions are better understood not in terms of damage to a dedicated declarative memory system, but in terms of impoverished representations of the stimuli those regions maintain.

It's All Coming Back to Me Now: Perception and Memory in Amnesia

Medial temporal lobe (MTL) structures may constitute a representational hierarchy, rather than a dedicated system for memory. Barense et al. (2012) show that intact memory for object features can interfere with perception of complex objects in individuals with MTL amnesia.

Benefits of immediate repetition versus long study presentation on memory in amnesia.

This study aimed to resolve discrepant findings in the literature regarding the effects of massed repetition and a single long study presentation on memory in amnesia. Experiment 1 assessed recognition memory in 9 amnesic patients and 18 controls following presentation of a study list that contained items shown for a single short study presentation, a single long study presentation, and three massed repetitions. In Experiment 2, the same encoding conditions were presented in a blocked rather than intermixed format to all participants from Experiment 1. In Experiment 1, control participants showed benefits associated with both types of extended exposure, and massed repetition was more beneficial than long study presentation, F(2, 34) = 14.03, p < .001, partial eta(2) = .45. In contrast, amnesic participants failed to show benefits of either type of extended exposure, F < 1. In Experiment 2, both groups benefited from repetition, but did so in different ways, F(2, 50) = 4.80, p = .012, partial eta(2) = .16. Amnesic patients showed significant and equivalent benefit associated with both types of extended exposure, F(2, 16) = 5.58, p = .015, partial eta(2) = .41, but control participants again benefited more from massed repetition than from long study presentation, F(2, 34) = 23.74, p < .001, partial eta(2) = .58. The findings suggest that previous inconsistencies in the literature were due to procedural differences across studies. We discuss group differences in terms of the mechanisms by which both forms of extended exposure facilitate performance in each group.

Not all repetition is alike: Different benefits of repetition in amnesia and normal memory

While it is well known that repetition can enhance memory in amnesia, little is known about which forms of repetition are most beneficial. This study compared the effect on recognition memory of repetition of words in the same semantic context and in varied semantic contexts. To gain insight into the mechanisms by which these forms of repetition affect performance, participants were asked to make Remember/Know judgments during recognition. These judgments were used to make inferences about the contribution of recollection and familiarity to performance. For individuals with intact memory, the two forms of repetition were equally beneficial to overall recognition, and were associated with both enhanced Remember and Know responses. However, varied repetition was associated with a higher likelihood of Remember responses than was fixed repetition. The two forms of repetition also conferred equivalent benefits on overall recognition in amnesia, but in both cases, this enhancement was manifest exclusively in enhanced Know responses. We conclude that the repetition of information, and especially repetition in varied contexts, enhances recollection in individuals with intact memory, but exclusively affects familiarity in patients with severe amnesia.

Recall and recognition memory in amnesia: Patients with hippocampal, medial temporal, temporal lobe or frontal pathology

The relationship between recall and recognition memory impairments was examined in memory-disordered patients with either hippocampal, medial temporal, more widespread temporal lobe or frontal pathology. The Hirst [Hirst, W., Johnson, M. K., Phelps, E. A., & Volpe, B. T. (1988). More on recognition and recall in amnesics. Journal of Experimental Psychology: Learning, Memory, & Cognition, 14, 758–762] technique for titrating exposure times was used to match recognition memory performance as closely as possible before comparing recall memory scores. Data were available from two different control groups given differing exposure times. Each of the patient groups showed poorer recall memory performance than recognition scores, proportionate to the difference seen in healthy participants. When patients’ scores were converted to Z-scores, there was no significant difference between mean Z-recall and Z-recognition scores. When plotted on a scatterplot, the majority of the data-points indicating disproportionately low recall memory scores came from healthy controls or patients with pathology extending into the lateral temporal lobes, rather than from patients with pathology confined to the medial temporal lobes. Patients with atrophy extending into the parahippocampal gyrus (H+) performed worse than patients with atrophy confined to the hippocampi (H−); but, when H− patients were given a shorter exposure time (5 s) and compared with H+ at a longer exposure (10 s), their performance was virtually identical and did not indicate any disproportionate recall memory impairment in the H− group. Parahippocampal volumes on MRI correlated significantly with both recall and recognition memory. The possibility that findings were confounded by inter-stimulus artefacts was examined and rejected. These findings argue against the view that hippocampal amnesia or memory disorders in general are typically characterised by a disproportionate impairment in recall memory. Disproportionate recall memory impairment has been observed in a number of published cases, and the reason for the varying pattern obtained across hippocampal patients requires further examination.

The anatomy of amnesia: Neurohistological analysis of three new cases

The most useful information about the anatomy of human memory comes from cases where there has been extensive neuropsychological testing followed by detailed post-mortem neurohistological analysis. To our knowledge, only eight such cases have been reported (four with medial temporal lobe damage and four with diencephalic damage). Here we present neuropsychological and post-mortem neurohistological findings for one patient (NC) with bilateral damage to the medial temporal lobe and two patients (MG, PN) with diencephalic damage due to bilateral thalamic infarction and Korsakoff's syndrome, respectively. All three patients exhibited a similar phenotype of amnesia with markedly impaired declarative memory (anterograde and retrograde) but normal performance on tests of nondeclarative memory (e.g., priming and adaptation-level effects) as well as on tests of other cognitive functions. Patient NC had damage to the hippocampus (dentate gyrus and the CA1 and CA3 fields) and layer III of the entorhinal cortex, but with relative sparing of the CA2 field and the subiculum. Patient MG had damage to the internal medullary lamina and mediodorsal thalamic nuclei. Patient PN had damage to the mammillary nuclei, mammillothalamic tracts, and the anterior thalamic nuclei. These findings illuminate several issues regarding the relation between diencephalic and medial temporal lobe amnesia, the status of recognition memory in amnesia, and the neuroanatomy of memory.

The contribution of familiarity to associative memory in amnesia

In Experiment 1, using the remember/know paradigm with control participants, we compared the contribution of recollection and familiarity to associative recognition for compound stimuli and for unrelated word pairs. It was demonstrated that familiarity makes a greater contribution to associative recognition of compound stimuli than to associative recognition of unrelated word pairs. In Experiment 2, we examined associative recognition memory in medial temporal lobe amnesics, diencephalic amnesics, and control participants for the stimuli employed in Experiment 1. Whereas associative recognition for compounds and unrelated words was nearly identical in control participants, associative recognition was higher for compounds than for unrelated word pairs in amnesic patients. This pattern was observed in the medial temporal amnesic group as well as in the diencephalic amnesic group. These results suggest that associative recognition in amnesia is enhanced to the extent that performance can be supported by study-induced familiarity for the studied pair.

Impaired Implicit Memory for Gist Information in Amnesia.

In 2 experiments using a converging associates paradigm, the authors evaluated implicit memory for gist information in amnesic patients. In Experiment 1, participants saw multiple sets of associates, each converging on a nonpresented theme word, and were then tested using an implicit word stem completion test and an explicit cued recall test. Amnesic patients showed intact implicit and impaired explicit memory for studied words, but memory for nonpresented lures was impaired, regardless of retrieval instructions. To evaluate whether impaired implicit memory for lures was due to accelerated forgetting of gist information, short study lists were used in Experiment 2, each consisting of a single set of associates. Amnesics' implicit memory for lures was again impaired. These results point to an inability to encode robust gist representations as the cause of impaired gist memory in amnesia.

The scope of preserved procedural memory in amnesia.

The finding that patients with amnesia retain the ability to learn certain procedural skills has provided compelling evidence of multiple memory systems in the human brain, but the scope, defining features and ecological significance of the preserved mnemonic abilities have not yet been explored. Here, we tested the hypothesis that subjects with amnesia would be able to learn and retain a broad range of procedural skills, by examining their acquisition and retention performance on five novel experimental tasks. The tasks are based on real-world activities and encompass a broad range of perceptual-motor demands: (i) the weaving task involves weaving pieces of fabric from woollen strings, using a manual weaver's loom; (ii) the geometric figures task consists of tracing geometric figures with a stylus as they move horizontally across a touch screen monitor; (iii) the control stick task involves tracking a sequence of visual target locations using a joystick control; (iv) the pouring task consists of pouring 200 ml of water from a watering can into a series of graduated cylinders, from a point 20 cm above the cylinders; and (v) the spatial sequence task involves learning an ordered sequence of pushing five spatially distributed buttons without visual guidance. Ten chronic and stable amnesic subjects (nine with bilateral medial temporal lobe damage due to herpes simplex encephalitis or anoxia, and one with thalamic stroke) and 25 matching normal comparison subjects were tested on three occasions: initial learning at time 1; retention at time 2 (24 h later); and retention at time 3 (2 months later). Despite impaired declarative memory for the tasks, the amnesic subjects demonstrated acquisition and retention of the five skills; their learning slopes over repeated trials were comparable with those of comparison subjects. These findings indicate that preserved learning of complex perceptual-motor skills in patients with amnesia is a robust phenomenon, and that it can be demonstrated across a variety of conditions and perceptual-motor demands. The comparability of the tasks employed in this study with real-world activities highlights the potential application of this memory dissociation in the rehabilitation of patients with amnesia.

Recall and recognition in mild hypoxia: using covariance structural modeling to test competing theories of explicit memory

To test theories of explicit memory in amnesia, we examined the effect of hypoxia on memory performance in a group of 56 survivors of sudden cardiac arrest. Structural equation modeling revealed that a single-factor explanation of recall and recognition was insufficient to account for performance, thus contradicting single-process models of explicit memory. A dual-process model of recall in which two processes (e.g., declarative memory and controlled search) contribute to recall performance, whereas only one process (e.g., declarative memory) underlies recognition performance, also failed to explain the results adequately. In contrast, a dual-process model of recognition provided an acceptable account of the data. In this model, two processes—recollection and familiarity—underlie recognition memory, whereas only the recollection process contributes to free recall. The best-fitting model was one in which hypoxia and aging led to deficits in recollection, but left familiarity unaffected. Moreover, a controlled search process was correlated with recollection, but was not associated with familiarity or the severity of hypoxia. The results support models of explicit memory in which recollection depends on the hippocampus and frontal lobes, whereas familiarity-based recognition relies on other brain regions.

Recognition memory in amnesia: Effects of relaxing response criteria

In two experiments, using the remember/know paradigm, we examined whether recognition memory in amnesic patients can be improved by instructing patients to relax their response criterion. Experiment 1 was modeled after a study by Dorfman, Kihlstrom, Cork, and Misiaszek (1995), in which direct instructions to respond more leniently led to an increase in recognition accuracy in patients with ECT-induced amnesia. We failed to extend this finding to patients with global amnesia, but the manipulation was unsuccessful in control subjects as well. In Experiment 2, response criterion was manipulated indirectly by providing information about the alleged base rate of study items on the recognition test. This manipulation led to a criterion shift in control subjects and enhanced discriminability in amnesic patients. Analysis of "remember" and "know" responses suggests that improved accuracy in amnesia was associated with enhanced familiarity-based recognition.

The relationship between recall and recognition in amnesia: Effects of matching recognition between patients with amnesia and controls.

To examine the relationship between recall and recognition memory in amnesia, the authors conducted 2 experiments in which recognition memory was equated between patients with amnesia and control participants. It was then determined whether recall was also similar across groups. In Experiment 1, recognition was equated by providing amnesic patients with additional study exposures; in Experiment 2, recognition was equated by testing controls following a longer delay. These different methods of equating recognition across groups led to divergent results because amnesic patients' recall performance was lower than controls' recall performance in Experiment 1 but not in Experiment 2. These findings are accounted for by considering the differential contribution of recollection and familiarity to the performance of amnesic patients and controls in the 2 experiments.

Word repetition in amnesia. Electrophysiological measures of impaired and spared memory.

Amnesic patients often show improved performance when stimuli are repeated, even in the absence of conscious memory for those stimuli. Although these performance changes are typically attributed to perceptual or motor systems, in some cases they may be related to basic language processing. We examined two neurophysiological measures that vary with word repetition in 12 amnesic patients and 12 control subjects: (i) a late positive component of the event-related potential (ERP) linked to conscious memory and (ii) the N400 component that varies with language comprehension. In each trial, the subject heard a category name, then viewed a word, and then decided whether the word was semantically congruous or incongruous (e.g. 'yes' for 'baby animal: cub'; 'no' for 'water sport: kitchen'). Recall and recognition testing at the end of the experiment showed that control subjects had better memory for congruous than for incongruous words, as did the amnesic patients, who performed less well overall. In contrast, amnesic patients were unimpaired on the category decisions required in each trial and, like the control subjects, showed a large N400 for incongruous relative to congruous words. Similarly, when incongruous trials were repeated after 0-13 intervening trials, N400s were reduced in both groups. When congruous trials were repeated, a late positive repetition effect was observed, but only in the control group. Furthermore, the amplitude of the late positive repetition effect was highly correlated with later word recall in both patients and controls. In the patients, the correlation was also observed with memory scores from standardized neuropsychological tests. These data are consistent with a proposed link between the late positive repetition effect and conscious memory. On the other hand, the N400 repetition effect was not correlated with episodic memory abilities, but instead indexed an aspect of memory that was intact in the amnesic patients. The preserved N400 repetition effect is an example of preserved memory in amnesia that does not easily fit into the categories of low-level perceptual processing or of motor learning. Instead, the sensitivity of the N400 to both semantic context and repetition may reflect a short-term memory process that serves language comprehension in realtime.

Role of Perceptual and Organizational Factors in Amnesics' Recall of the Rey-Osterrieth Complex Figure: A Comparison of Three Amnesic Groups

To examine the contribution of visual-perceptual and visual-organizational factors to visual memory in amnesia, Korsakoff, medial temporal, and anterior communicating artery (ACoA) aneurysm amnesics' copy, organization, and recall performance on the Rey-Osterrieth Complex Figure was assessed. Korsakoff patients were matched to medial temporal patients in terms of severity of amnesia, while the ACoA group, which was less severely amnesic, was matched to the Korsakoff patients on performance on executive tasks. Results indicated that while both the ACoA and Korsakoff groups had poorer copy accuracy and organization than controls, only the Korsakoff patients' copy accuracy was worse than the other two amnesic groups. While the Korsakoff patient's visuoperceptual deficits could partially explain this group's poor performance at immediate recall, the Korsakoff group's comparatively worse performance at delayed recall could not be accounted for by poor copy accuracy, reduced visual organization, or even the combined influence of these two factors.

The effect of semantic categorisation on recall memory in amnesia.

Amnesic patients were compared to a healthy control group on recall of word lists containing semantically-related or unrelated words. As expected on the basis of previous literature, the amnesic group performed below the control group on all measures of recall. When total recall scores for each list were used as the index of performance, their scores were not significantly affected by the type of list, unlike those of the control group. Comparison of serial position effects for different parts of the lists revealed that the control group derived greater benefit from semantic relatedness in recall of items from the middle positions. This effect was not shown by the amnesic group, who showed similar U-shaped serial position curves for recall of all three lists, and appeared to use a more passive recall strategy than the control group. The findings are discussed in relation to our current understanding of amnesic deficits.