Preserved semantic learning in an amnesic patient

A case study is reported of an amnesic patient (KN), who displayed an ability to learn a substantial body of new visual and verbal semantic concepts, despite having a severe deficit in episodic memory. In two experiments, using an errorless learning paradigm, he was able to perform at a level close to that of his wife, who served as a control subject. When recall of material was retested after a delay of several months, during which time there were no further learning sessions, his retention was at least as good as, if not better, than that of his wife. This is taken as further evidence for the dissociation of semantic and episodic processes in amnesia. It also provides further evidence for the role of "errorless learning" in efficient acquisition of new facts in amnesia.     

The anterograde and retrograde retrieval ability of a patient with amnesia due to encephalitis

A patient with amnesia due to encephalitis was previously described in 1976 as having normal short-term memory and an intact ability to perform semantic analysis. Despite this ability, his retention beyond the limits of short-term memory was nearly nil. The present investigation sought to evaluate more completely the nature of this patient's retrieval deficit using a series of paradigms developed subsequent to his initial testing. Once again it was discovered that while his intact analytic abilities allowed retention of material in working memory, as soon as that working capacity was exceeded, retrieval of information became nearly impossible. It became apparent that the patient could not discriminate between a cue's most recently analyzed associate and the strongest existing associate to that cue in his semantic hierarchy. An analysis of his retrograde memory ability showed that he could retrieve almost no real episodes of either a public or private nature from his past. Instead, he seemed to rely on generalizations from his semantic memory to reconstruct “probable” events.     

Acquired amnesia in childhood: a single case study

We report the case of C.L., an 8-year-old child who, following the surgical removal of an ependymoma from the left cerebral ventricle at the age of 4 years, developed significant difficulties in retaining day-to-day events and information. A thorough neuropsychological analysis documented in C.L. a severe anterograde amnesic syndrome, characterised by normal short-term memory, but poor performance on episodic long-term memory tests. In particular, C.L. demonstrated virtually no ability to recollect new verbal information several minutes after the presentation. As for semantic memory, C.L. demonstrated general semantic competencies, which, depending on the test, ranged from the level of a 6-year-old girl to a level corresponding to her actual chronological age. Finding a patient who, despite being severely impaired in the ability to recollect new episodic memories, still demonstrates at least partially preserved abilities to acquire new semantic knowledge suggests that neural circuits implicated in the memorisation of autobiographical events and factual information do not overlap completely. This case is examined in the light of growing literature concerned with the dissociation between episodic and semantic memory in childhood amnesia.     

A Comparison of 'Errorless' and 'Trial-and-error' Learning Methods for Teaching Individuals with Acquired Memory Deficits

We present nine experiments, in three study phases, which test the hypothesis that learning methods which prevent the making of errors (“errorless learning”) will lead to greater learning than “trial-and-error” learning methods amongst individuals who are memory impaired as a result of acquired brain injury. Results suggest that tasks and situations which facilitate retrieval of implicit memory for the learned material (such as learning names with a first letter cue) will benefit from errorless learning methods, whilst those that require the explicit recall of novel associations (such as learning routes or programming an electronic organiser) will not benefit from errorless learning. The more severely amnesic patients benefit to a greater extent from errorless learning methods than those who are less severely memory impaired, but this may only apply when the interval between learning and recall is relatively short.     

The role of episodic memory in semantic learning: An examination of vocabulary acquisition in a patient with amnesia due to encephalitis

Abstract

Four experiments examined the ability of the densely amnesic patient SS to acqulre novel vocabulary that entered the language after the onset of his amnesla. Experiment 1 examined SS's ability to recall and recognize the meaning of novel words; Experiment 2 utilized a semantic priming paradigm to assess his knowledge of these words under conditions in which the retrieval demands were minimized; Experiment 3 evaluated his lexical knowledge of novel words in a lexical decision task; Experiment 4 used a sentence verification paradigm to evaluate his ability to discern the correct use of novel words. SS was severely impaired across all taska. Only when the novel words were compound words consisting of well known parts, was there any evidence to suggest that he had acquired even partial knowledge about these words. This pattern of results was not attributable to a generalized semantic memory deflcit. Rather, these findings suggest that episodic memory plays an important role in the acquisltion of novel semantic Information.     

Impaired recruitment of the dorsolateral prefrontal cortex and hippocampus during encoding in bipolar disorder.

BACKGROUND: The aim of the present study was to examine the functional neuroanatomy of episodic memory impairment in euthymic subjects with bipolar I disorder. There is evidence that individuals with bipolar disorder have cognitive impairments not only during mood episodes but also when they are euthymic. The most consistently reported cognitive difficulty in euthymic subjects with bipolar disorder is impairment in verbal episodic memory (i.e., the ability to learn new verbal information). METHODS: The current study examined verbal learning in eight euthymic, remitted subjects with bipolar I disorder (BP-I; seven nonmedicated) and eight control subjects matched for age, gender, education, and intelligence. Subjects underwent (15)O-CO(2) positron emission tomography scanning while completing a verbal learning paradigm that consisted of encoding (learning) several lists of words. RESULTS: The BP-I subjects had more difficulties learning the lists of words compared with the control subjects. Compared with control subjects, BP-I subjects exhibited blunted regional cerebral blood flow (rCBF) increases in the left dorsolateral prefrontal cortex (Brodmann's area 9/46) during encoding. CONCLUSIONS: Consistent with previous studies, subjects with BP-I were impaired in learning new verbal information. This was associated with rCBF abnormalities in brain regions involved in learning and episodic memory.     

Dissociation of explicit and implicit long-term memory consolidation in semantic dementia: A case study

We report a case study of a semantic dementia patient, whose episodic memory consolidation was tested over a 2-month period. The results reveal that despite early retention of information, the patient lost all explicit information of the newly learnt material after 2 weeks. By contrast, he retained implicit word information even after a 4-week delay. These findings highlight the critical time window of 2–4 weeks in which newly learnt information should be re-encoded in rehabilitations studies. The results also indicate that learnt information can be still accessed with implicit retrieval strategies when explicit retrieval fails.     

How do Korsakoff patients learn new concepts?

The goal of the present investigation was to assess semantic learning in Korsakoff patients (KS), compared with uncomplicated alcoholics (AL) and control subjects (CS), taking the nature of the information to-be-learned and the episodic memory profiles of the three groups into account.Ten new complex concepts, each illustrated by a photo and composed of a label, a category and three features, were taught to 13 KS, 23 AL and 45 CS. When examined independently of the main experimental task, the two patients’ groups presented episodic memory, working memory and executive impairments but episodic memory was more severely impaired in KS.Both AL and KS exhibited label learning deficits but KS were more severely impaired than AL. The episodic memory results were the main factor accounting for label learning performance when the three groups were pooled together. When examined within each group, the correlation was significant in CS and AL but not in KS. Only KS exhibited impaired category and feature learning results. Episodic memory did not account for category and feature learning performance.New label learning may be equivalent to that of proper names, requiring the involvement of episodic memory notably to arbitrarily associate a meaningless word with a specific identity. However, when episodic memory is severely impaired like in KS, an alternative neocortical learning route, bypassing episodic memory, may be invoked. Category and feature seem to be acquired independently of episodic memory. The specific impairment in category and feature learning in KS may therefore reflect a genuine deficit of semantic memory in Korsakoff's syndrome.     

Functional retrograde amnesia: A quantitative case study

The memory impairment of a patient suffering from functional retrograde amnesia was assessed both during amnesic episode and after its termination. The patient's performance on a task tapping semantic memory was nearly identical on the two test occasions, but his performance on a task tapping episodic memory substantially changed across test sessions. Cueing procedures revealed that in spite of the patient's restricted access to episodic memory during the amnesic period, a relatively intact “island” of episodic memories could be uncovered. The distinction between episodic and semantic memory, as well as the relation between organic and functional retrograde amnesia, are discussed in light of the case study.     

Hippocampal activation during episodic and semantic memory retrieval: comparing category production and category cued recall

Whether or not the hippocampus participates in semantic memory retrieval has been the focus of much debate in the literature. However, few neuroimaging studies have directly compared hippocampal activation during semantic and episodic retrieval tasks that are well matched in all respects other than the source of the retrieved information. In Experiment 1, we compared hippocampal fMRI activation during a classic semantic memory task, category production, and an episodic version of the same task, category cued recall. Left hippocampal activation was observed in both episodic and semantic conditions, although other regions of the brain clearly distinguished the two tasks. Interestingly, participants reported using retrieval strategies during the semantic retrieval task that relied on autobiographical and spatial information; for example, visualizing themselves in their kitchen while producing items for the category kitchen utensils. In Experiment 2, we considered whether the use of these spatial and autobiographical retrieval strategies could have accounted for the hippocampal activation observed in Experiment 1. Categories were presented that elicited one of three retrieval strategy types, autobiographical and spatial, autobiographical and nonspatial, and neither autobiographical nor spatial. Once again, similar hippocampal activation was observed for all three category types, regardless of the inclusion of spatial or autobiographical content. We conclude that the distinction between semantic and episodic memory is more complex than classic memory models suggest.     

Assessment of memory skills in illiterates: strategy differences or test artifact?

Previous studies have reported that illiterates perform more poorly than literates on a variety of neuropsychological measures. We investigated the hypothesis that putative memory deficits in illiterates are an artifact of the assessment tools used rather than a reflection of an 'underdeveloped' ability. In order to accomplish this, we designed two tests, a word list learning test and an object learning test. The illiterate group performed more poorly than semiliterate and literate groups on most variables of the word list learning test, but only on delayed recall and semantic clustering on the object learning test. Our findings suggest that poor memory performance among illiterates can be attributed both to the nature of the task, as well as to the use of different cognitive mechanisms to recall learned information. Presumably, formal education may enhance the innate ability of learning through training individuals in efficient learning and retrieval strategies. We emphasize the importance of developing and using ecologically valid neuropsychological tests to assess illiterate individuals.     

A new frontier in spaced retrieval memory training for persons with Alzheimer's disease

The objective of this pilot study was to investigate how a memory training technique called "Spaced Retrieval" (SR) might be effectively applied in helping persons with Alzheimer's disease improve their recall of recent events. Capitalising on the interdependence among spared and impaired memory systems, it was hypothesised that SR training with support at encoding and retrieval would facilitate the retention and recall of meaningful recent events. Eight participants with a diagnosis of Alzheimer's disease or related disorder were recruited for this study. The study employed a quasi-experimental multiple baseline treatment design across participants, items, and behaviours. SR training was provided in three domains: Semantic, Prospective, and Episodic recent memory. The results show important training gains made by all participants across conditions at post-training follow-up. In the Episodic condition, participants were able to recall specific details about recent events following training. This study provides preliminary evidence that individuals with mild to severe cognitive impairment can learn and recall new episodic information through Spaced Retrieval training. If replicated, these findings would support the use of Spaced Retrieval as an intervention tool to help individuals maintain their functioning in the area of episodic recent memory.     

The effect of retrieval cues on post-retrieval monitoring in episodic memory: an electrophysiological study

The aim of the present experiment was to examine whether episodic retrieval and 'post-retrieval' monitoring are affected by the nature of the cue that guides a search of memory. We recorded event-related brain potentials (ERPs) from young healthy adult participants while they tried to recall studied words (e.g. 'MOTHER') with the aid of word-stem (e.g. 'MOT') and word-fragment (e.g. 'M-TH--') retrieval cues. Analyses of the behavioural data showed that while it was far more difficult to generate completions per se for the fragments, the levels of conscious, or 'explicit', recall obtained with each type of cue were statistically identical. ERP analyses focussed upon differences in neural activity evoked by each type of cue (termed 'old/new' ERP effects) during successful versus unsuccessful retrieval. The stem and fragment old/new ERP effects were remarkably similar in their time course and magnitude, and also in their scalp distribution, which changed over time as multiple neuronal populations, and hence multiple cognitive operations, became activated. These behavioural and ERP findings suggest that the cognitive operations reflected by old/new effects in cued recall tasks may be insensitive to changes in the retrieval strategy, or effort, that participants apply to monitor the episodic status of retrieved information. The findings are discussed in relation to previous ERP and functional imaging studies that have investigated task-specific features of retrieval and post-retrieval processing in episodic memory.     

Searching for the anatomical basis of retrograde amnesia

Abstract

The case of a patient with profound retrograde and minor anterograde amnesia is described and used to discuss the kind of brain damage which will most likely result in persistent retrograde amnesia as the principal symptom. The patient was an industrial manager who had fallen off a horse four years prior to the present neuropsychological and neuroradiological investigation. MRI examination revealed an injury to both temporal poles and to the latero-ventral portion of the right prefrontal cortex. The prefrontal and temporal cortical damage on the right side deeply invaded the white matter while the temporal cortical damage on the left side was much smaller; here, however, portions of the temporo-parietal transition zone were affected as well. The patient was of average intelligence. His attention, short-term memory, and learning ability were average or somewhat below average. His old memories were severely affected in the personal-episodic domain, and much less so in that of semantic remote memory. We conclude from this case that the necessary anatomical substrate for the retrieval of old episodic memories lies within the anterior temporal regions (including deeper situated fiber projections) and possibly involves an interaction with the prefrontal cortex, and that this damage is dissociable from the medial temporal-lobe damage leading to anterograde amnesia.     

Functional ("psychogenic") amnesia

Patients who present with severely impaired memory functioning without a discernable neurological cause typically have experienced one or more severely stressful life events. These patients, who are described as having "psychogenic" or "dissociative" amnesia, typically differ from patients with the neurologic amnestic syndrome in that memory for their personal life histories is much more severely affected than is their ability to learn and retain new information; that is, they have isolated retrograde amnesia. Recent cognitive and brain imaging research has begun to reveal some of the cerebral mechanisms underlying functional amnesia, but this disorder remains best conceptualized as a relatively rare form of illness-simulating behavior rather than a disease. Neuropsychological assessment is often useful in revealing the circumscribed nature of the patient's performance deficits, the spared functions that can be brought to bear in rehabilitation, and the emotional disorders requiring psychiatric treatment. Controlled treatment trials are nonexistent, but case reports suggest that supportive psychotherapy, systematic relaxation training, hypnosis, and sedative/anxiolytic medications are useful in facilitating recovery. These treatments are often combined with a psychoeducational approach that essentially reteaches the patient his or her life story.     

A Consequence of Failed Sequential Learning: A Computational Account of Developmental Amnesia

Developmental amnesia, featured with severely impaired episodic memory and almost normal semantic memory, has been discovered to occur in children with hippocampal atrophy. Such amnesia seems to challenge the understanding that early loss of episodic memory may impede cognitive development and result in severe mental retardation. While the underlying mechanism is still unclear, no computational model has been reported to simulate developmental amnesia. A cognitive and computational system is presented, for the first time, to simulate the unique characteristics of the amnesia: impaired episodic recall, spared recognition, and spared semantic learning. The lesioned sequential/spatial learning ability of the hippocampus is suggested to be able to cause severe impairment of episodic recall, but affect neither recognition ability nor semantic learning. Semantic learning is generally thought to largely associate with the consolidation of episodic memory, a process in which sequential activation of episodic memory may not be necessary. Semantic learning through memory consolidation featured with random activation of stored experiences is performed, and the acquired knowledge is demonstrated to have the flexibility that is one of the key characteristics of semantic memory.     

Can zebrafish learn spatial tasks? An empirical analysis of place and single CS-US associative learning

The zebrafish may be an ideal tool with which genes underlying learning and memory can be identified and functionally investigated. From a translational viewpoint, relational learning and episodic memory are particularly important as their impairment is the hallmark of prevalent human neurodegenerative diseases. Recent reports suggest that zebrafish are capable of solving complex relational-type associative learning tasks, namely spatial learning tasks. However, it is not known whether good performance in these tasks was truly based upon relational learning or upon a single CS-US association. Here we study whether zebrafish can find a rewarding stimulus (sight of conspecifics) based upon a single associative cue or/and upon the location of the reward using a method conceptually similar to 'context and cue dependent fear conditioning' employed with rodents. Our results confirm that zebrafish can form an association between a salient visual cue and the rewarding stimulus and at the same time they can also learn where the reward is presented. Although our results do not prove that zebrafish form a dynamic spatial map of their surroundings and use this map to locate their reward, they do show that these fish perform similarly to rodents whose hippocampal function is unimpaired. These results further strengthen the notion that complex cognitive abilities exist in the zebrafish and thus they may be analyzed using the excellent genetic tool set developed for this simple vertebrate.     

Benefits and limitations of errorless learning after surviving pediatric brain tumors: a case study

Survivors of childhood brain tumors often acquire complex cognitive difficulties including impairments in attention, processing speed, and different aspects of memory function. These impairments can affect their learning in the real world and in the classroom. However, the efficacy of memory rehabilitation techniques post treatment has not yet been assessed in these patients. We present the case of a 15-year-old boy, C.J., who acquired a profound episodic memory impairment due to a metastatic germ cell tumor and subsequent treatment. The focus of this study was the application of an errorless learning technique to a verbal learning task. We were interested to test whether C.J. would benefit from errorless learning as compared to errorful learning. Results of an experiment and a follow-up study indicated that C.J.'s learning was more efficient under errorless conditions, although access to the information from long-term memory remained cue dependent. Implications for learning with or without the support of episodic memory are discussed, and future directions for memory rehabilitation of brain tumor survivors are outlined.     

Face-name association learning in early Alzheimer's disease: a comparison of learning methods and their underlying mechanisms

This study compared the efficacy of five learning methods in the acquisition of face-name associations in early dementia of Alzheimer type (AD). The contribution of error production and implicit memory to the efficacy of each method was also examined. Fifteen participants with early AD and 15 matched controls were exposed to five learning methods: spaced retrieval, vanishing cues, errorless, and two trial-and-error methods, one with explicit and one with implicit memory task instructions. Under each method, participants had to learn a list of five face-name associations, followed by free recall, cued recall and recognition. Delayed recall was also assessed. For AD, results showed that all methods were efficient but there were no significant differences between them. The number of errors produced during the learning phases varied between the five methods but did not influence learning. There were no significant differences between implicit and explicit memory task instructions on test performances. For the control group, there were no differences between the five methods. Finally, no significant correlations were found between the performance of the AD participants in free recall and their cognitive profile, but generally, the best performers had better remaining episodic memory. Also, case study analyses showed that spaced retrieval was the method for which the greatest number of participants (four) obtained results as good as the controls. This study suggests that the five methods are effective for new learning of face-name associations in AD. It appears that early AD patients can learn, even in the context of error production and explicit memory conditions.     

Memory and brain--neurobiological correlates of memory disturbances

A differentiation of memory is possible on the basis of chronological and contents-related aspects. Furthermore, it is possible to make process-specific subdivisions (encoding, transfer, consolidation, retrieval). The time-related division on the one hand refers to the general differentiation into short-term and long-term memory, and, on the other, to that between anterograde and retrograde memory ("new" and "old memory"; measured from a given time point, usually that when brain damage occurred). Anterograde memory means the successful encoding and storing of new information; retrograde the ability to retrieve successfully acquired and/or stored information. On the contents-based level, memory can be divided into five basic long-term systems--episodic memory, the knowledge system, perceptual, procedural and the priming form of memory. Neural correlates for these divisions are discussed with special emphasis of the episodic and the knowledge systems, based both on normal individuals and brain-damaged subjects. It is argued that structures of the limbic system are important for encoding of information and for its transfer into long-term memory. For this, two independent, but interacting memory circuits are proposed--one of them controlling and integrating primarily the emotional, and the other primarily the cognitive components of newly incoming information. For information storage principally neocortical structures are regarded as important and for the recall of information from the episodic and semantic memory systems the combined action of portions of prefrontal and anterior temporal regions is regarded as essential. Within this fronto-temporal agglomerate, a moderate hemispheric-specificity is assumed to exist with the right-hemispheric combination being mainly engaged in episodic memory retrieval and the left-hemispheric in that of semantic information. Evidence for this specialization comes from the results from focally brain-damaged patients as well as from that functional brain imaging in normal human subjects. Comparing results from imaging studies in memory disturbed patients with brain damage and from patients with a psychiatric diagnosis (e. g., psychogenic amnesia) revealed that both patient groups demonstrate comparable metabolic changes on the brain level. It can therefore be concluded that in neurological patients distinct, identifiable tissue damage is existent, while in psychiatric patients changes in the brain's biochemistry (release of stress hormones, and transmitters) constitute the physiological bases for the memory disturbances.