Improved verbal learning in the semantic variant of primary progressive aphasia when using semantic cues

The semantic variant of primary progressive aphasia (PPA-S) is characterized by impairments in confrontation naming and single word comprehension. Although episodic memory may be relatively spared, there can be impairment in verbal learning tasks. We report a patient with PPA-S and impaired verbal learning who was tested to learn if when provided with semantic categories, her learning would improve. A 70-year-old right-handed woman with a 2-year history of progressive difficulties with word finding, naming, and memory was tested for language and memory deficits using the Hopkins Verbal Learning Test-Revised (HVLT-R). She was then retested with the HVLT-R after being provided with the three semantic categories to which these words belonged. Confrontation naming was impaired on the Boston Naming Test. Sentence repetition was normal. Comprehension testing with word picture matching and sentence comprehension was normal. On a test of semantic associations, Pyramids and Palm Trees, she was impaired. She was also impaired on tests of verbal learning (HVLT-R) (total: 13) but not recall. When a different version of the HVLT-R was given with the semantic categories of the words given beforehand, her scores improved (total: 26). This patient with PPA-S had an impairment of verbal learning, but not delayed recall. When given a semantic category cue beforehand, her verbal learning performance improved. This observation suggests that this patient did not spontaneously use semantic encoding. Using a semantic cueing strategy may help other patients with PPA-S improve their capacity for verbal learning.     

Priming deficits in amnesia: now you see them, now you don't.

The rate with which perceptual information becomes available was manipulated in 2 word naming experiments. Word priming effects, in terms of reduced naming latencies for repeated items, and recognition memory measures were obtained with matched groups of amnesic patients and control participants. In both experiments, the amnesic patients evidenced significantly reduced priming effects compared to control participants under difficult task conditions. Under easy task conditions the baseline naming latencies of the amnesics were significantly longer than those of controls, but the difference in priming effects failed to reach significance. The findings are consistent with the Information Availability model of priming positing that both priming and explicit memory are mediated by episodic information from a study or information processing episode. It is argued that word priming does not represent a memory function that is spared in amnesia.     

Repetition effects in a lexical decision task: the role of episodic memory in the performance of alcoholic Korsakoff patients

To examine the contribution of episodic memory to the successful verbal priming performance of Korsakoff patients, we adapted a lexical decision task which holds constant the processing demands during study and testing. Words and nonwords were repeated at a lag of 0, 1, 3, 8 and 15 items and the decrease in response latency was taken as a measure of priming. In Experiment 1, Korsakoff patients showed repetition priming of a magnitude similar to that obtained by alcoholic controls, even at a lag of 15 intervening items. Experiment 2 explored the effect of word frequency on repetition priming. Korsakoff patients again showed normal priming up to lags of 15, and, as expected, these repetition effects were larger for low frequency than for high frequency words. This outcome was felt to be more consistent with an episodically based familiarity account than with a semantic activation account. Finally, Korsakoff patients were found to be impaired in their ability to use episodic memory in an explicit memory task that used the same material under comparable presentation conditions (Experiment 3). Contemporary processing models of episodic memory are discussed as possible explanations for the successful implicit memory performance by amnesic patients on this task.     

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.     

Semantic acquisition without memories: evidence from transient global amnesia.

Transient global amnesia (TGA), characterised by a profound anterograde amnesia, is a model of interest to study the acquisition of novel meanings independent of episodic functioning. Three patients were tested during a TGA attack, two in the early recovery phase and the third during the acute phase of TGA, with a semantic priming task involving a restructuring process of conceptual knowledge. During TGA, all patients demonstrated priming effects. Results obtained the day after the episode with the same task showed that these effects persisted at least one day. Episodic memory seems not to be critical for the formation of novel connections among unrelated semantic representations, in accordance with Tulving's model of memory, i.e. episodic memory is not necessary for the acquisition of semantic information.     

Episodic and semantic memory after traumatic brain injury in a child]

In an early-life, a memory disturbance affects the learning and school record directly. Furthermore, it may cause the problem of maltreatment or adaptation difficulty for school life. We report a child amnesia caused by a traumatic brain injury when she was 9 years old. We examined her episodic and semantic memory. We developed 3-steps tasks of recognition and recall for the post-accident episodic memory. First, the examiner presented the patient with four words orally including a label of her episode, and asked her to choose one that she felt familiar with (the recognition of the episodic label). Second, if the word she selected was correct, she was required to recall the episode related to the word (the recall of the episode). Third, if she could not recall the episode herself correctly, she was required to choose a correct sentence about the episode (the recognition of the episode). She could not recall episodes correctly, but produced confabulation instead. She showed, however, good recognition of each episode. Furthermore, we performed recognition tests of time, person, and place about the same post-accident episodes, which were poor especially for time. In semantic memory tasks, we examined about kanji characters (ideogram) learned from the first grade to the sixth grade and mathematical knowledge learned from the second grade to the sixth grade at elementary school ("What centimeters is equal to one meter?" or "Tell me the formula of the size of a circle." etc). We found that she showed a retrograde impairment for about one year. For both episodic and semantic memory, she showed an anterograde impairment. Because of the anterograde amnesia she could not acquire new facts, and also showed para-amnesia or confabulation. In a child with brain damage, neuropsychological assessment is important in predicting effect of rehabilitation and recovery of school performance.     

Increased neural efficiency in the temporal association cortex as the result of semantic task repetition

We examined the effect of semantic task repetition and of alternating between tasks on cerebral blood flow in three H(2) (15)O positron emission tomography experiments. We found that repeatedly performing semantic tasks resulted in a reduction in cerebral blood flow to the left temporal association cortex similar to that found in priming experiments even though here there was no repetition of stimuli. Although the same effect was found in two different tasks (word meaning judgments and picture naming), it was only present when the same task was repeated on consecutive scans and not when the subjects alternated from scan to scan between tasks. We propose that there is a neural efficiency which develops in the association cortex of the temporal lobe as a result of repeatedly performing a semantic task. This efficiency is abolished by interruptions such as performing a different task.     

Repetition priming of picture naming in semantic aphasia: The impact of intervening items

Background: We present an experiment that explores the nature of repetition priming of picture naming in a group of semantic stroke aphasic patients. The study was designed to extend previous investigations of repetition priming effects among other stroke aphasic patients and patients with semantic dementia. This work builds on previous work with semantic aphasic patients that shows enhanced picture-naming performance due to correct phonemic cues.

Aims: To assess the extent to which semantic control deficits observed during semantic aphasic patients' picture naming are resolved by prior exposure to an identical stimulus, and to determine the optimal lag between prime and target to maximise naming success.

Methods & Procedures: The procedure was carried out with five stroke patients who had all failed verbal and picture versions of tests of semantic association, revealing difficulties with manipulation of semantic information, and their performance was compared to five age- and education-matched controls. A total of 180 pictures to be named were presented individually on a computer screen in two sessions at least a week apart, with half preceded by an identical item in session one and the other half preceded by an identical item in session two. Three lags (0, 1, and 7 items intervening) were embedded in the pseudo-random structure such that it was unpredictable whether the next trial would be a repeat or not.

Outcomes & Results: Considerable repetition priming was observed in this semantic aphasic patient group, bringing their performance up to control level at lag 0. Priming with a very short lag between prime and target (0–1 item) significantly reduced latency. Accuracy was significantly increased and semantic errors decreased with up to seven intervening items. Controls also benefited from repetition priming, but showed little variation in latency, accuracy or errors over this range of short lags.

Conclusions: For patients with problems manipulating semantic information, repetition priming was an effective way to boost naming performance, although increasing the number of intervening items had a progressively detrimental effect. The observed repetition priming effects are interpreted within a connectionist model of speech production.     

A case of amnesia at an early age

A dissociation between short- and long-term memory (LTM) and between the episodic and the semantic component of LTM is reported in a young girl who became amnesic at the age of 6 after an episode of acute encephalopathy resulting in bilateral frontal, insular, thalamic, ponto-mesencephalic, hippocampal and temporal lesions, as documented by MRI. The girl became amnesic a few months after starting school. A follow-up investigation showed that she was able to learn to read, write and acquire number facts and procedures and to improve her semantic knowledge. Our results show that the features of adult amnesia can also be found in children and that new semantic knowledge can be acquired in spite of an anterograde memory deficit. This dissociation does not agree with theories viewing long- term declarative memory as a unitary process mediated by the hippocampal system, but supports recent hypotheses that the acquisition of semantic knowledge is independent from episodic memory processes, and takes place through spared cortical regions subjacent to the hippocampi (Vargha-Khadem et al., 1997).     

Neuropsychological and SPECT scan findings during and after transient global amnesia: evidence for the differential impairment of remote episodic memory.

A patient had neuropsychological testing during, and at two days and seven weeks after a transient global amnesia (TGA) attack. During the attack she exhibited a characteristically profound anterograde amnesia but a limited remote memory loss; the most striking impairment was a deficit in personal episodic memory revealed by her performance on the Autobiographical Memory Interview. Personal and general semantic information was less impaired although there were indications of a temporal gradient in the impairment. When tested after the attack, she demonstrated normal anterograde and retrograde memory. A SPECT scan performed during TGA showed a focal reduction in cerebral perfusion in the postero-medial temporal lobes bilaterally which had resolved after seven weeks.     

Semantic memory and frontal executive function during transient global amnesia.

To assess semantic memory and frontal executive function, two patients underwent neuropsychological testing during transient global amnesia (TGA) and after an interval of 6-8 weeks. In spite of a profound deficit in anterograde verbal and non-verbal memory, semantic memory was normal, as judged by category fluency measures, picture naming, and picture-word and picture-picture matching, and reading ability was normal. Similarly, there were no deficits on a number of tests known to be sensitive to frontal executive dysfunction. A hexamethylpropyleneamine-oxime (HMPAO) single photon emission CT (SPECT) scan, obtained on one patient 24 hours post-TGA, showed focal left temporal lobe hypoperfusion which had resolved three months later. The observed dissociation between episodic and semantic memory is discussed in the light of contemporary cognitive theories of memory organisation.     

Event-related brain potentials that distinguish false memory for events that occurred only seconds in the past

ABSTRACT: BACKGROUND: False memory often involves retrieving events from the distant past that did not actually happen. However, recent evidence obtained using the Deese/Roediger-McDermott (DRM) paradigm for eliciting false memory experiences suggests that individuals can falsely believe that events occurred mere seconds in the past when they in fact did not. Subjects in these experiments endorsed unstudied critical lure words as having been studied, despite the fact that word lists were studied just moments before. We identified event-related brain potential (ERP) correlates of this experience, and included a repetition priming manipulation to better assess the functional significance of these ERPs. METHODS: Behavioral and ERP data were collected from 21 Capital Normal University students using a short-term DRM task. RESULTS: Two categories of effects were identified that distinguished true from false short-term memory: (1) early semantic priming effects from 300 to 500 ms and (2) later retrieval and retrieval-monitoring effects after 500 ms. The repetition priming manipulation had distinct influences on these effects, consistent with their differential associations with semantic priming versus episodic retrieval. CONCLUSION: Characterization of ERPs related to semantic priming and episodic retrieval provides important information regarding the mechanisms of short-term false memory. In contrast, most studies examining false memory in standard long-delay DRM paradigms identify ERP effects related only to retrieval monitoring. These findings highlight the neural processing involved in illusions of memory after very brief delays and highlight the role of semantic processing in short-term false memory.     

Re-visiting "semantic facilitation" of word retrieval for people with aphasia: facilitation yes but semantic no

Previous research has shown that word-to-picture matching for targets that cannot be named at pre-test results in improved naming relative to untreated control items for people with aphasia. This paper replicates and extends this finding and investigates its source. Is the effect a result of priming of semantic representations, or of post-semantic mechanisms in word retrieval? The first experiment shows that word-to-picture matching with unrelated distractors improves naming at short (2-3 minutes) and long (up to 25 minute) lags. There was no effect of being made aware of the relationship between word-to-picture matching and picture naming. People who have a semantic impairment improve only with a short lag between word-to-picture matching and naming. Participants with less semantic impairment show larger priming effects that are equal at short and long lags between word-to-picture matching and naming. The second experiment shows that the facilitation effect is just as large for word-to-picture matching with unrelated distractors as with semantically-related distractors. Furthermore, overall there was no difference between matching with coordinate items and with associated items. The results of these experiments show that facilitation of naming by word-to-picture matching in people with aphasia cannot be a result of the priming of semantic representations. Instead they are consistent with two effects: word-to-picture matching results in priming at a lemma level for aphasic people with a semantic impairment that is only found with a short lag between word-to-picture matching and naming. Word-to-picture matching causes priming of the lemma to output lexicon entry mapping that benefits participants with less semantic impairment that is evident at both a short and long lag between word-to-picture matching and naming. These findings fit well with previous research on repetition priming of naming with normal subjects.     

Episodic and semantic memory in children with mesial temporal sclerosis

The aim of this study was to analyze semantic and episodic memory deficits in children with mesial temporal sclerosis (MTS) and their correlation with clinical epilepsy variables. For this purpose, 19 consecutive children and adolescents with MTS (8 to 16 years old) were evaluated and their performance on five episodic memory tests (short- and long-term memory and learning) and four semantic memory tests was compared with that of 28 healthy volunteers. Patients performed worse on tests of immediate and delayed verbal episodic memory, visual episodic memory, verbal and visual learning, mental scanning for semantic clues, object naming, word definition, and repetition of sentences. Clinical variables such as early age at seizure onset, severity of epilepsy, and polytherapy impaired distinct types of memory. These data confirm that children with MTS have episodic memory deficits and add new information on semantic memory. The data also demonstrate that clinical variables contribute differently to episodic and semantic memory performance.     

Editorial: Cognitive Neuroscience of Memory

Abstract

The anatomical and neurophysiological bases of memory have been significantly advanced by integrative approaches bridging previously existing gaps between individual neuroscientific disciplines. The time- and content-based division of memory has been widely accepted: episodic and semantic memory, procedural memory and priming are frequently used terms. On the anatomical side, a division into forms of memory dependent on the limbic system (episodic and semantic information) and others (procedural memory and priming) being independent of these regions, has gained entrance into cognitive neuroscience as well. More disputed are ideas on the possible representation of stored information in the brain and on the existence of regions centrally implicated in its retrieval. Even more controversial are possible similarities between psychogenic and organic forms of amnesia. The present overview discusses these and related issues and points to some possibilities for integration. Last, but not least, this overview introduces the nine individual contributions making up this special issue on brain-memory interrelations.     

The underlying mechanisms of semantic memory loss in Alzheimer's disease and semantic dementia

Patients with Alzheimer's disease (AD) and patients with semantic dementia (SD) both exhibit deficits on explicit tasks of semantic memory such as picture naming and category fluency. These deficits have been attributed to a degradation of the stored semantic network. An alternative explanation attributes the semantic deficit in AD to an impaired ability to consciously retrieve items from the semantic network. The present study used an implicit lexical-decision priming task to examine the integrity of the underlying semantic network in AD and SD patients matched for degree of impairment on explicit semantic memory tasks. The AD (n=11) and SD (n=11) patient groups were matched for age, education, level of dementia and impairment on four explicit semantic memory tasks. Healthy elderly participants (n=22) were matched for age and education. Semantic priming effects were evaluated for three types of semantic relationships (attributes, category coordinates, and category superordinates) and compared to lexical associative priming. Healthy controls showed significant priming across all conditions. In contrast, AD patients showed normal superordinate priming, and significant (although somewhat reduced) coordinate priming, but no attribute priming. SD patients showed no priming effect for any semantic relationship. All groups showed significant associative priming. The results indicate that SD patients do indeed have substantial degradation of semantic memory, while AD patients have a partially intact network, accounting for priming in superordinate and coordinate conditions. These findings suggest that AD patients' impairment on explicit semantic tasks is the product of deficient explicit retrieval in combination with a partially degraded semantic network.     

A case of cerebral infarction presenting as retrosplenial amnesia]

We report a 73-year-old right-handed female who presented with an acute amnesic syndrome. On November 18, 1991, she was admitted to a local hospital complaining of sudden-onset vertigo and nausea, but immediately after the admission she developed an amnesic syndrome. On November 27, she was transferred to our hospital for further assessment of her memory disturbance. Neurologically she was normal except for mild right hemianopsia and increased deep tendon reflexes in the extremities. Neuropsychological assessments were performed over 3 weeks. She was always alert, attentive, and cooperative. She had no confabulation. On the Wechsler Adult Intelligence Scale revised (WAIS-R), her total IQ was 110. Frontal, verbal, and perceptual functions and motor performance were normal. She had no signs of a callosal disconnection. Despite these preserved functions, her memory function was obviously disturbed. Several memory betteries showed that her recent memory for both verbal and visual modalities was impaired, while her immediate memory such as digit span was preserved. For remote memory her retrograde episodic memory concerning both personal and public events was almost intact, although she had a profound anterograde amnesia. In particular she recalled her personal information about just-premorbid events in detail. On the other hand, her semantic memory, for example understanding of proverbs, geography, and scientific law, was preserved. Taken together, her procedural memory on learning tasks, such as "Tower of Hanoi" and mirror drawing, was intact. Computed tomography demonstrated a low-density area medial to the trigon of the left ventricle.(ABSTRACT TRUNCATED AT 250 WORDS)     

The nature of lexico-semantic processing deficits in mild cognitive impairment

Lexico-semantic impairments in Alzheimer disease (AD) have been attributed to abnormalities in both intentional and automatic access to semantic memory. However, the order in which these impairments appear during the course of the disease is unclear. We sought to answer this question by documenting lexico-semantic impairments in 61 subjects with mild cognitive impairment (MCI), a pre-AD stage, and by comparing them to those of 39 AD and 60 normal elderly (NE) subjects. All subjects were tested with intentional access tasks (picture naming and semantic probes), automatic access tasks (lexical decision and priming), and executive function tasks (Stroop and Stroop-Picture naming). Results indicated that the MCI group was only impaired on tasks of intentional access relative to the AD group who was impaired on both types of tasks. Because most MCI subjects eventually develop AD, these results suggest that intentional access to semantic memory is impaired before automatic access. Further, impairments on the Stroop-Picture naming task but not on the Stroop task, suggest that lexico-semantic impairments in the MCI group may be related to inhibition deficits during semantic search. Findings are discussed in light of executive dysfunctions within the framework of semantic memory theories.     

Increased inhibition and decreased facilitation effect during a lexical decision task in children

Widespread theories propose that implicit memory is established in the early stages of development, while explicit memory continues to develop until later stages. However, recent studies have argued that implicit memory changes developmentally. In order to elucidate the differences of implicit memory and semantic memory structures between children and adults, a single-word presentation method was developed using lexical decision tasks in which repeated real words, related real words, unrelated real words and pseudowords were presented in a list. Semantic priming and repetition priming using a single-word presentation method were employed in 25 children and 18 adults. Reaction time (RT) and correct rate for real words following pseudowords served as the base. Inhibition effect was defined as an increase in RT between a real word preceded by an unrelated real word and a real word preceded by a pseudoword. Facilitation effect was defined as a decrease in RT between a real word preceded by a related real word and a real word preceded by a pseudoword. Although the effect sizes of semantic priming did not differ between children and adults, the inhibition effect was larger and the facilitation effect was smaller in children. Repetition priming in children did not differ from that in adults. These findings challenge the idea of developmental invariance in implicit memory, suggesting that the strength of links between nodes in the semantic network increases and the range of spreading activation expands developmentally.     

Deficits in egocentric-updating and spatial context memory in a case of developmental amnesia

Patients with developmental amnesia usually suffer from both episodic and spatial memory deficits. DM, a developmental amnesic, was impaired in her ability to process self-motion (i.e., idiothetic) information while her ability to process external stable landmarks (i.e., allothetic) was preserved when no self-motion processing was required. On a naturalistic and incidental episodic task, DM was severely and predictably impaired on both free and cued recall tasks. Interestingly, when cued, she was more impaired at recalling spatial context than factual or temporal information. Theoretical implications of that co-occurrence of deficits and those dissociations are discussed and testable cerebral hypothesis are proposed.