The dynamic time course of memory recovery in transient global amnesia

AIMS: To investigate the dynamic time course of transient global amnesia (TGA)--that is, the process of recovery and the interindividual variability--by testing four patients during the day of TGA itself (on three occasions) and at follow up (on two occasions). METHODS: A specially designed protocol focusing on semantic (both conceptual and autobiographical knowledge) and episodic (both anterograde and retrograde components) memory. RESULTS: Every patient showed marked impairment of both anterograde and retrograde episodic memory during the acute phase, with a relative preservation of personal and conceptual semantic knowledge. During the following phase, the authors observed similarities and differences among the patients' patterns of recovery. In general, retrograde amnesia recovered before the anterograde amnesia and anterograde episodic memory was recovered gradually in every case. In contrast, shrinkage of retrograde amnesia was more heterogeneous. In two of the patients, this shrinkage followed a chronological gradient and the most remote events were recovered first. In the two other patients, it depended more on the strength of the trace, and there was no temporal gradient. For the latter, an executive deficit could account for difficulties in accessing both conceptual knowledge and autobiographical memories. CONCLUSIONS: This profile of recovery suggests a "neocortical to medial temporal" process in every case, and the possibility of an additional frontal dysfunction in some cases. Hence, the acute phase seems to be characterised by a common episodic impairment. This variability between subjects appears in the recovery phase with two different patterns of impairment.     

Extensive temporally graded retrograde amnesia for personal-episodic facts in transient global amnesia

Abstract

Transient global amnesia (TGA) is characterized by an impairment of episodic memory resulting both in anterograde and retrograde amnesia. Few studies have assessed retrograde amnesia in TGA. Only Evans et al. (Journal of Neurology, Neurosurgery and Psychiatry 1993; 56: 1227-30) have distinguished between the episodic and semantic components of autobiographical memory, suggesting a disturbance of autobiographical incident recollection. A patient was tested during the acute phase of TGA with a sophisticated autobiographical event interview [derived from Kopelman et al. (Journal of Clinical and Experimental Neuropscyhology 1989; 11: 724-44) and Borrini et al. (Psychological Medicine 1989; 19: 215-24)], designed to replicate and extend this study of autobiographical memory. The autobiographical event interview disclosed an extensive disturbance in recalling memories with a temporal gradient, sparing earliest memories compared to more recent ones.     

Episodic, but not semantic, autobiographical memory is reduced in amnestic mild cognitive impairment

Amnestic mild cognitive impairment (aMCI) is characterized by decline in anterograde memory as measured by the ability to learn and remember new information. We investigated whether retrograde memory for autobiographical information was affected by aMCI. Eighteen control (age 66-84 years) and 17 aMCI (age 66-84 years) participants described a personal event from each of the five periods across the lifespan. These events were transcribed and scored according to procedures that separate episodic (specific happenings) from semantic (general knowledge) elements of autobiographical memory. Although both groups generated protocols of similar length, the composition of autobiographical recall differentiated the groups. The aMCI group protocols were characterized by reduced episodic and increased semantic information relative to the control group. Both groups showed a similar pattern of recall across time periods, with no evidence that the aMCI group had more difficulty recalling recent, rather than remote, life events. These results indicate that episodic and semantic autobiographical memories are differentially affected by the early brain changes associated with aMCI. Reduced autobiographical episodic memories in aMCI may be the result of medial temporal lobe dysfunction, consistent with multiple trace theory, or alternatively, could be related to dysfunction of a wider related network of neocortical structures. In contrast, the preservation of autobiographical semantic memories in aMCI suggests neural systems, such as lateral temporal cortex, that support these memories, may remain relatively intact.     

Autobiographical memory in progressive supranuclear palsy

Background: We aimed to investigate recall of autobiographical memories across lifetime periods in patients with progressive supranuclear palsy (PSP). Method: Patients with PSP (n = 10) were given a test of autobiographical and personal semantic information and the Addenbrooke’s Cognitive Examination (ACE). The result was compared to 30 matched neurologically intact participants. Result: A mild autobiographical memory impairment was observed in PSP without a temporal gradient for the recall of autobiographical or personal semantic information. Performance correlated with verbal fluency in ACE. Conclusion: Patients with PSP show mild deficits in autobiographical memory, which is likely to reflect a frontal retrieval deficit.     

The effect of impaired verbal memory retrieval on autobiographical memory across different life periods in schizophrenia

ObjectivesAutobiographical memory (AM) involves recollection of personal events and facts about one's life. Αim of the present study was to investigate AM in schizophrenia patients, and, in particular, patients' ability to recall autobiographical memories after controlling for verbal memory and verbal fluency deficits.MethodParticipants included 40 schizophrenia patients (23 male) and 40 healthy controls (23 male), matched for age, gender, educational level, and premorbid intellectual functioning. Participants' verbal memory (list learning and story recall) and verbal fluency were assessed. AM was evaluated by the Questionnaire of Autobiographical Memory, consisting of the Personal Semantic Memory scale and the Autobiographical Incidents scale. Furthermore, personal incidents' specificity was examined.ResultsSchizophrenia patients showed deficits in verbal memory and verbal fluency, as well as in both semantic and episodic AM compared with healthy controls. Deficits were shown in episodic and semantic memories of events and facts dating to three different life periods (childhood, early adulthood and recent life). Regarding specificity of recalled events, patients reported fewer specific autobiographical incidents than controls. After controlling AM deficits for patients' verbal memory and verbal fluency impairment, it was shown that schizophrenia patients recalled fewer memories of autobiographical incidents dating only to recent life, compared with healthy controls.ConclusionsSchizophrenia patients showed impaired AM after controlling for verbal memory and verbal fluency impairment only in regard with personal episodic memories from recent life. Current findings raise the important issue of cognitive remediation therapy in schizophrenia.     

Anterograde and retrograde amnesia in a person with bilateral fornix lesions following removal of a colloid cyst

AD, a 45-year-old man, presented with a severe and global anterograde amnesia following surgery for removal of a colloid cyst. Structural neuroimaging confirmed bilateral lesions to the fornix and a small lesion in the basal forebrain. Testing for remote episodic memory of autobiographical events, and for remote semantic memory of personal and public events, and of famous people, revealed that AD had a severe retrograde amnesia for autobiographical episodes that covered his entire lifetime, and a time-limited retrograde amnesia for semantic memory. Because the fornix and basal forebrain lesions disrupted major afferent and efferent pathways of the hippocampus, it was concluded that the integrity of the hippocampus and its projections are needed to retain and/or recover autobiographical memories no matter how old they are. By contrast, hippocampal contribution to semantic memory is time-limited. These findings were interpreted as consistent with Multiple Trace Theory, which holds that the hippocampal system is essential for recovering contextually rich memories no matter how old they are, but is not needed for recovering semantic memories.     

Retrieval mechanisms for autobiographical memories: insights from the frontal variant of frontotemporal dementia

Very few studies have investigated autobiographical memory in the frontal variant of frontotemporal dementia (fv-FTD). The aim of this study was therefore to unravel the mechanisms of autobiographical memory disruption in general and in the anterograde and retrograde components of amnesia in particular, in patients suffering from fv-FTD. An autobiographical memory task assessing overall (AM) and strictly episodic memories (EM) from five lifetime periods covering the entire lifespan revealed the absence of a temporal gradient for both scores, suggesting the existence of a retrieval deficit. An analysis of the correlation between these two scores and a general cognitive assessment of executive function, working, episodic (i.e. new learning ability) and semantic memory, and behavioural changes highlighted the considerable involvement of executive function, semantic memory and, to a lesser degree, episodic memory and behavioural changes. Moreover, step-wise regression analyses performed on the EM score revealed that the executive function was a better predictor of the retrograde component than of the anterograde component, which was linked principally to new episodic learning ability. All these results confirm the impact of executive dysfunction on autobiographical deficits in fv-FTD, and suggest that the mechanisms at the root of autobiographical memory disruption may also involve difficulties in new episodic learning and semantic storage, though this may be due to the fact that we studied an advanced form of fv-FTD.     

A case of persistent retrograde amnesia following a dissociative fugue: neuropsychological and neurofunctional underpinnings of loss of autobiographical memory and self-awareness

Autobiographical memory relies on complex interactions between episodic memory contents, associated emotions and a sense of self-continuity over the course of one's life. This paper reports a study based upon the case of the patient NN who suffered from a complete loss of autobiographical memory and awareness of identity subsequent to a dissociative fugue. Neuropsychological, behavioral, and functional neuroimaging tests converged on the conclusion that NN suffered from a selective retrograde amnesia following an episode of dissociative fugue, during which he had lost explicit knowledge and vivid memory of his personal past. NN's loss of self-related memories was mirrored in neurobiological changes after the fugue whereas his semantic memory remained intact. Although NN still claimed to suffer from a stable loss of autobiographical, self-relevant memories 1 year after the fugue state, a proportionate improvement in underlying fronto-temporal neuronal networks was evident at this point in time. In spite of this improvement in neuronal activation, his anterograde visual memory had been decreased. It is posited that our data provide evidence for the important role of visual processing in autobiographical memory as well as for the efficiency of protective control mechanisms that constitute functional retrograde amnesia.     

Impairment of episodic and semantic autobiographical memory in patients with mild cognitive impairment and early Alzheimer's disease

Autobiographical memory includes the retrieval of personal semantic data and the remembrance of incident or episodic memories. In retrograde amnesias, it has been observed that recall of autobiographical memories of recent events is poorer than recall of remote memories. Alzheimer's disease (AD) may also be associated with a temporal gradient (TG) in memory decline, though studies have yielded inconsistent results on this point. They have also yielded inconsistent results on whether AD might differentially affect semantic and episodic remembrance. Here, we compared autobiographical memory of childhood, early adulthood, and recent life among healthy control (HC) subjects, patients with early AD, and patients with amnesic mild cognitive impairment (aMCI). Both the aMCI and AD patients exhibited declines in recall of autobiographical incidents and semantic information. In AD patients, both components of autobiographical memory had a clear TG, with better preservation of memories of childhood than those of early adulthood and recent life. The TG of autobiographical memory decline in AD patients is more compatible with the Cortical Reallocation Theory than with the Multiple Trace Theory of memory consolidation. In contrast to AD patients, aMCI patients exhibited impaired recall of personal facts and autobiographical incidents relating only to recent life. The significant decline in autobiographical memory for recent life that occurred in aMCI patients suggests that deterioration of consolidation of personal facts and events begins with commencement of functional impairment in the hippocampus.     

Episodic memory and self-awareness in Asperger Syndrome: Analysis of memory narratives

Previous findings from researchers on individuals with Asperger Syndrome (AS) suggest peculiarities of autobiographical memory (AM). They have shown a personal episodic memory deficit in the absence of a personal semantic memory impairment. The primary aim of this study was to explore AM in individuals with AS, and more specifically to investigate the link between episodic memory, self-awareness, and autonoetic consciousness through language analysis. We asked fifteen adults with AS and fifteen age- and IQ-matched controls to recall autobiographical memories from three life periods. Recorded interviews were processed using Alceste software. We found that participants with AS recalled fewer and less-detailed episodic memories than did controls. A content analysis revealed that family-related vocabulary as well as possessive pronouns was significantly less frequent in AS interviews than in those of controls. In conclusion, our results support the hypothesis that a deficiency of episodic memory may be due to poor awareness of the self in social relationships. Reduced use of possessive pronouns may also indicate less self-investment in life experiences, which would in turn impact recall.     

Medial temporal lobe structures are needed to re-experience remote autobiographical memories: evidence from H.M. and W.R

The nature and extent of retrograde amnesia in patients with medial temporal lobe (MTL) lesions is currently under debate. While some investigators propose a temporally limited role for the MTL in episodic and semantic memory, others claim that MTL structures are needed for episodic memories of one's entire lifetime, and that only semantic memory becomes independent of the MTL. To address this issue, we tested two amnesic patients, H.M. and W.R., with bilateral MTL lesions on a series of remote memory tests that together distinguished episodic memory from semantic memory performance. Notably, we used a new method to assess autobiographical memory that measured the degree of re-experiencing of personal happenings from the past. Both patients showed relatively spared semantic memory, but severe impairment on measures of autobiographical memory, with no temporal gradient. Our data support the view that MTL structures play a significant role in recalling specific personal episodes, not only from the recent past but from the distant past as well.     

Alteration of autobiographical memory in amnestic mild cognitive impairment

The concept of amnestic mild cognitive impairment (aMCI) concerns a population of older individuals at high risk of developing probable Alzheimer's disease. Although anterograde memory deficits have been largely documented in patients with aMCI, little is known about the integrity of their autobiographical memory (AuM). This study aimed at evaluating AuM in aMCI individuals and at investigating whether their ability to retrieve AuMs varied as a function of whether the tests used required recognition or effortful retrieval processes. Fourteen aMCI patients and 14 matched controls underwent a standard neuropsychological evaluation and an extensive autobiographical assessment. AuM was explored using verbal material, the Autobiographical Memory Interview, and a visual task of personal photographs. Together, these tests tapped the semantic and episodic components of AuM and different cognitive processes involved in retrieval (recall and recognition). Results indicate that AuM is altered in aMCI patients. This impairment affects both episodic and semantic components of AuM, and is characterized by a general difficulty in recollecting personal episodes covering the entire lifespan, along with a loss of recognition of recently experienced episodes. Furthermore, recollection of personal episodes was correlated with scores on tests requiring retrieval abilities, while recognition of familiar photographs was correlated with scores on tests assessing encoding/storage of new information. Results suggest that the AuM deficit in aMCI patients may result from the combination of two mechanisms, an anterograde memory impairment impeding the storage of newly experienced events, and a global alteration of recollection affecting the recall of AuM covering all periods of life. Alteration of these processes may possibly be related to the progression and distribution of the neuropathological lesions in medial temporal and frontal lobe structures found in Alzheimer's disease.     

Autobiographical memory, the sense of recollection and executive functions after severe traumatic brain injury

Residual disorders of autobiographical memory long after trauma resulting from head injury are rarely assessed, even though they may affect social adjustment and the resumption of daily life. We conducted a thorough study of autobiographical memory in severe traumatic brain injury (TBI) patients, examined at least one year post-trauma. Twenty-five patients were submitted to a novel and controlled autobiographical procedure specially designed to measure episodic memories (i.e., unique, specific in time and space, and detailed) from their entire life span with two kinds of self-remembering experience. The ability to mentally travel back through time and re-experience the source of acquisition, i.e. autonoetic consciousness, was assessed via the "Remember/Know" paradigm and a checking procedure of sense of remembering. Self-perspective in visual imagery, which is also critically involved in episodic recollection, was assessed by the "Field/Observer perspective" paradigm. In addition, the patients underwent a battery of standardized neuropsychological tests to assess episodic and semantic memory, orientation and executive functions. The results showed that the patients, compared with healthy controls, were significantly impaired in recalling episodic autobiographical memories. This impairment was not related to the life period tested or the patients' ages nor the intellectual impairment. Deficits involved disturbances in sense of remembering, visual imagery self-perspective and recollection of spatiotemporal details. Stepwise-regression analyses carried out in the TBI patients revealed a significant relationship between an abnormal sense of remembering and executive dysfunction covering both anterograde and retrograde components. The novel assessment used in this study provides the first detailed evidence of a more fine-grained deficit of autobiographical memory in TBI patients. Indeed, the results suggest that these patients, long after trauma, present autonoetic consciousness and self-perspective disorders, which include sense of identity (the self) as a continuous entity across time, probably related to frontal dysfunction.     

Two further investigations of autobiographical memory in semantic dementia

A number of investigations in semantic dementia have documented better retrieval of recent personal events compared to those in the more distant past (Graham and Hodges, 1997). Westmacott et al. (2001) challenged this result, however, finding relative preservation of remote memories in a single case of semantic dementia when he was tested using family photographs. In Experiment 1, we tested two possible explanations for the discrepancy between the published papers: (a) that there is a significant effect of modality in autobiographical retrieval in semantic dementia (e.g., patients will show better, or even preserved, remote memory when tested on nonverbal, compared to verbal, tasks); and (b) that the distinct pattern seen between patients is attributable to the different methods adopted for scoring the episodic quality of the memories. A patient with semantic dementia, AM, produced autobiographical memories to both words and family photographs. These personal events were scored by two raters using the scoring method described by Westmacott et al. (2001) and that reported by Graham and Hodges (1997). It was found that AM showed similar levels of remote memory impairment regardless of whether the cue was verbal or nonverbal. In addition, significant effects of time were revealed in AM's performance on the verbal memory test, regardless of which method was used to score the memories. In Experiment 2, we investigated a related question: whether the relatively better retrieval of memories in semantic dementia could be due to over rehearsal of highly salient recent experiences? Four patients were tested on their ability to remember a recent event (either a trip to London or events from a Formula One Grand Prix race) using specially designed autobiographical questionnaires. It was found that all four were able to perform this task, although one patient showed evidence of some forgetting over three months, and another exhibited difficulty discriminating between two similar events. Together, the two experiments further confirm that patients with semantic dementia show a modality independent autobiographical memory deficit, with better retrieval of recent events.     

Remote episodic memory deficits in patients with unilateral temporal lobe epilepsy and excisions.

The nature of remote memory impairment in patients with medial temporal lobe damage is the subject of some debate. While some investigators have found that retrograde amnesia in such patients is temporally graded, with relative sparing of remote memories (Squire and Alvarez, 1995), others contend that impairment is of very long duration and that remote memories are not necessarily spared (Sanders and Warrington, 1971; Nadel and Moscovitch, 1997). In this study, remote memory was assessed in 25 patients with unilateral temporal lobe epilepsy and 22 non-neurologically impaired controls using the Autobiographical Memory Interview (Kopelman et al., 1989). Results indicate that patients have impaired personal episodic memory but intact personal semantic memory. The impairment extends even to the most remote time periods in early childhood, long before seizure onset in many patients. As well, patients awaiting temporal lobectomy for control of seizures perform as poorly as those who have already undergone resective surgery. These results support the hypothesis that temporal lobe damage or dysfunction, caused by recurrent seizures or surgical excision, results in extensive retrograde amnesia for personal episodic memories. Interestingly, patients with radiological evidence of hippocampal sclerosis were not significantly more impaired than those without obvious sclerosis. These results indicate that even minimal damage to medial temporal lobes results in significant impairment to autobiographical episodic memory. These findings are more compatible with a memory loss or retrieval deficit rather than a consolidation account of remote memory impairment.     

Episodic and semantic memory in mild cognitive impairment

Little is known about episodic and semantic memory in the early predementia stage of Alzheimer's disease (AD), which is referred to as mild cognitive impairment (MCI). To explore person knowledge, item recognition and spatial associative memory, we designed the Face Place Test (FPT). A total of 75 subjects participated: 22 patients with early AD, 24 with MCI and 29 matched controls. As predicted, AD patients showed significant deficits in person naming, item recognition and recall of spatial location (placing). Surprisingly, subjects with MCI were also impaired on all components. There was no significant difference between AD and MCI except on the placing component. Analysis of the relationship between semantic (naming) and episodic (recognition and placing) components of the FPT revealed a significant association between the two episodic tasks, but not between episodic and semantic performance. Patients with MCI show deficits of episodic and semantic memory. The extent of impairment suggests dysfunction beyond the medial temporal lobe. The FPT might form the basis of a sensitive early indicator of AD.     

Personal semantic and episodic autobiographical memories in Korsakoff syndrome: A comparison of interview methods

Objective: The temporal gradient in patients with Korsakoff’s syndrome has been of particular interest in the literature, as many studies have found evidence for a steep temporal gradient, but others have observed more uniform remote memory impairment across all past time periods. Inconsistencies might be the result of the nature of remote memory impairment under study (i.e., nonpersonal or autobiographical memory) and of methodological differences in the examination of remote memory loss. The aim of this study was to examine whether differences between autobiographical memory interview (AMI) and autobiographical interview (AI) procedures influence the presence of a temporal gradient in semantic and episodic autobiographical memory in Korsakoff patients. Method: The procedure used in the present study combined the AMI and AI into one study session. We compared the performance of 20 patients with Korsakoff’s syndrome and 27 healthy controls. First, participants were asked to recall knowledge from different life periods. Second, participants were asked to recall memories from five life periods. Thirdly, participants were asked to rate their subjective experience of each event recalled on a 5-point scale. Finally, we analyzed the findings in terms of all the memories recalled versus the first memory from each life-period only. Results: Both the AMI and the AI showed a temporally graded retrograde amnesia in the Korsakoff patients for personal semantic and episodic autobiographical memories. The pattern of amnesia in Korsakoff patients was not affected by examining only one event per life-period. Subjective ratings of recalled memories were largely comparable between the groups. Conclusions: The findings were generally consistent across the AMI and AI. Varying the number of events did not affect the pattern of the gradient. Hence, the temporal gradient in Korsakoff patients is not an artefact of either the AMI or the AI method.     

Reduced levels of specific autobiographical memories in schizophrenia

Autobiographical memory is intrinsically related to the self and personal identity. This study investigated whether both personal episodic memory and semantic memory are impaired in schizophrenia, a disease characterized by an abnormal personal identity. Personal episodic memory and personal semantic memory were investigated in 24 patients with schizophrenia and 24 normal subjects using an autobiographical fluency task and an autobiographical memory inquiry. Autobiographical memory scores and the proportion of specific memories were lower in patients with schizophrenia than in normal subjects. The deficit of personal episodic and semantic memory, as assessed by the autobiographical memory inquiry and the autobiographical fluency task, respectively, was most apparent after the onset of clinical symptoms. Schizophrenia is associated with an impairment of both personal episodic and semantic memory and with a reduction of specific autobiographical memories. Those impairments are consistent with the existence of an abnormal personal identity in patients with schizophrenia.     

Behavioral and functional neuroanatomical correlates of anterograde autobiographical memory in isolated retrograde amnesic patient M.L.

Patient M.L. [Levine, B., Black, S. E., Cabeza, R., Sinden, M., Mcintosh, A. R., Toth, J. P., et al. (1998). Episodic memory and the self in a case of isolated retrograde amnesia. Brain, 121, 1951-1973], lost memory for events occurring before his severe traumatic brain injury, yet his anterograde (post-injury) learning and memory appeared intact, a syndrome known as isolated or focal retrograde amnesia. Studies with M.L. demonstrated a dissociation between episodic and semantic memory. His retrograde amnesia was specific to episodic autobiographical memory. Convergent behavioral and functional imaging data suggested that his anterograde memory, while appearing normal, was accomplished with reduced autonoetic awareness (awareness of the self as a continuous entity across time that is a crucial element of episodic memory). While previous research on M.L. focused on anterograde memory of laboratory stimuli, in this study, M.L.’s autobiographical memory for post-injury events or anterograde autobiographical memory was examined using prospective collection of autobiographical events via audio diary with detailed behavioral and functional neuroanatomical analysis. Consistent with his reports of subjective disconnection from post-injury autobiographical events, M.L. assigned fewer “remember” ratings to his autobiographical events than comparison subjects. His generation of event-specific details using the Autobiographical Interview [Levine, B., Svoboda, E., Hay, J., Winocur, G., & Moscovitch, M. (2002). Aging and autobiographical memory: dissociating episodic from semantic retrieval. Psychology and Aging, 17, 677-689] was low, but not significantly so, suggesting that it is possible to generate episodic-like details even when re-experiencing of those details is compromised. While listening to the autobiographical audio diary segments, M.L. showed reduced activation relative to comparison subjects in midline frontal and posterior nodes previously identified as part of the autobiographical memory network. Reductions were also evident in M.L. in association with personal semantic stimuli (e.g., recordings describing personal habits and routines). These data suggest an association between M.L.’s impoverished recollection of autobiographical material and reduced activation in midline sectors of the autobiographical memory network that support the autonoetic, first-person element of episodic memory.