The impairment of verbal semantic memory: a single case study.

We report our investigations of a single patient in whom there was a selective impairment of semantic memory. She had a marked deficit of individual word comprehension although other language and linguistic skills were relatively preserved. Here we document that her failures in word comprehension were stable over a long time period. She made "phonological" errors in defining meanings, which we argue are analogous to "visual" errors in reading. On verbal learning tasks her performance was shown to be relatively preserved, a finding which provides evidence of the dissociation of verbal semantic memory and episodic (event) memory.     

Verbal semantic memory in temporal lobe epilepsy

OBJECTIVES: Temporal lobe epilepsy (TLE) may determine memory difficulties not explained by episodic memory impairment. The present study was aimed to verify the presence of specific semantic memory dysfunctions in TLE and to explore their relations to epilepsy variables. SUBJECTS AND METHODS: Forty-seven patients with lateralized temporal (n = 26) or extra-temporal lobe epilepsy (n = 21) and 23 healthy subjects were compared. Picture Naming and Pointing to a Picture were used to explore expressive and receptive vocabulary and the Semantic Questionnaire evaluated semantic judgment of verbally presented items. The Selective Reminding Procedure for word list learning and Story Recall were used to assess episodic memory. Spontaneous speech and the Token Test controlled for language disturbances, and Raven's Coloured Progressive Matrices were used to evaluate abstract reasoning ability. RESULTS: Multivariate analysis of variance of test scores showed significant impairment of semantic memory in patients with left TLE compared to healthy controls, whereas episodic memory was impaired in left temporal and extra-temporal epilepsy (as measured by word learning) and all epilepsy groups (as measured by Story Recall). In the TLE groups, naming abilities were more compromised than single-word comprehension and semantic judgment - which were not significantly affected. No deficits in language abilities or in abstract reasoning were found in any patient group. Factor analysis of memory tests scores in the patients produced two factors, one semantic and the other episodic. Regression analysis revealed that the semantic factor was related to abstract reasoning, left hemisphere lateralization of seizures, and age of seizure onset; while the episodic factor was related to age. CONCLUSIONS: Left TLE may determine significant verbal semantic memory compromise, maybe due to impaired access to the semantic-lexical storage. In non-aphasic epilepsy patients, comparison of performance on semantic and episodic memory tests may be useful for assessing the nature of memory failures, and may complement clinical and neurophysiological means for defining the epileptic center.     

Lexicality effects in word and nonword recall of semantic dementia and progressive nonfluent aphasia

Background: Verbal working memory is an essential component of many language functions, including sentence comprehension and word learning. As such, working memory has emerged as a domain of intense research interest both in aphasiology and in the broader field of cognitive neuroscience. The integrity of verbal working memory encoding relies on a fluid interaction between semantic and phonological processes. That is, we encode verbal detail using many cues related to both the sound and meaning of words. Lesion models can provide an effective means of parsing the contributions of phonological or semantic impairment to recall performance.

Methods & Procedures: We employed the lesion model approach here by contrasting the nature of lexicality errors incurred during recall of word and nonword sequences by three individuals with progressive nonfluent aphasia (a phonological dominant impairment) compared to that of two individuals with semantic dementia (a semantic dominant impairment). We focused on psycholinguistic attributes of correctly recalled stimuli relative to those that elicited a lexicality error (i.e., nonword → word OR word → nonword).

Outcomes & Results: Patients with semantic dementia showed greater sensitivity to phonological attributes (e.g., phoneme length, wordlikeness) of the target items relative to semantic attributes (e.g., familiarity). Patients with PNFA showed the opposite pattern, marked by sensitivity to word frequency, age of acquisition, familiarity, and imageability.

Conclusions: We interpret these results in favour of a processing strategy such that in the context of a focal phonological impairment patients revert to an over-reliance on preserved semantic processing abilities. In contrast, a focal semantic impairment forces both reliance on and hypersensitivity to phonological attributes of target words. We relate this interpretation to previous hypotheses about the nature of verbal short-term memory in progressive aphasia.     

The role of the temporal lobe semantic system in number knowledge: evidence from late-stage semantic dementia

Previous reports have demonstrated that many aspects of number knowledge remain unimpaired in semantic dementia, despite severe comprehension problems in other domains. It is argued that this advantage for numbers arises because the disease spares the parietal lobe magnitude system thought to be critical for number processing. Models of numerical cognition that favour a separation between verbal and magnitude representations of number might, however, predict a restricted impairment of the verbal number code in this condition. We obtained support for this hypothesis in a patient with late-stage semantic dementia. She was impaired at a variety of tasks tapping the verbal number code; for example, reading and writing Arabic numerals, naming and word-picture matching with dot pictures, reading aloud number words, digit span and magnitude comparison/serial ordering tasks with number words. In contrast, she demonstrated good understanding of the magnitude and serial order of numbers when tested with Arabic numerals and non-symbolic representations. These findings suggest that although the magnitude meaning of numbers is isolated from the temporal lobe semantic system, the anterior infero-temporal lobe may play a critical role in binding English number words to their non-symbolic magnitude meaning.     

Non-verbal semantic impairment in semantic dementia

The clinical presentation of patients with semantic dementia is dominated by anomia and poor verbal comprehension. Although a number of researchers have argued that these patients have impaired comprehension of non-verbal as well as verbal stimuli, the evidence for semantic deterioration is mainly derived from tasks that include some form of verbal input or output. Few studies have investigated semantic impairment using entirely non-verbal assessments and the few exceptions have been based on results from single cases ([3]: Breedin SD, Saffran EM, Coslett HB. Reversal of the concreteness effect in a patient with semantic dementia. Cognitive Neuropsychology 1994;11:617-660, [12]: Graham KS, Becker JT, Patterson K, Hodges JR. Lost for words: a case of primary progressive aphasia? In: Parkin A, editor. Case studies in the neuropsychology of memory, East Sussex: Lawrence Erlbaum, 1997. pp. 83-110, [21]: Lambon Ralph MA, Howard D. Gogi aphasia or semantic dementia? Simulating and assessing poor verbal comprehension in a case of progressive fluent aphasia. Cognitive Neuropsychology, (in-press). This study employed sound recognition and semantic association tasks to investigate the nature of the verbal and non-verbal comprehension deficit in 10 patients with semantic dementia. The patients were impaired on both verbal and non-verbal conditions of the assessments, and their accuracy on these tasks was directly related to their scores on a range of other tests requiring access to semantic memory. Further analyses revealed that performance was graded by concept and sound familiarity and, in addition, identified significant item consistency across the different conditions of the tasks. These results support the notion that the patients' deficits across all modalities were due to degradation within a single, central network of conceptual knowledge. There were also reliable differences between conditions. The sound-picture matching task proved to be more sensitive to semantic impairment than the word-picture matching equivalent, and the patients performed significantly better on the picture than word version of a semantic association test. We propose that these differences arise directly from the nature of the mapping between input modality and semantic memory. Words and sounds have an arbitrary relationship with meaning while pictures benefit from a degree of systematicity with conceptual knowledge about the object.     

Progressive language impairment without dementia: a case with isolated category specific semantic defect.

A patient is described with a 5 year progressive defect of naming and auditory verbal comprehension, the pathological nature of which was presumably degenerative. The auditory comprehension defect unevenly affected different semantic categories, and was particularly severe for the names of animals, fruits and vegetables. The patients showed loss of the verbal knowledge of the physical attributes of the concepts corresponding to the words he was unable to understand, and sparing of the verbal knowledge of the functional attributes. His performance was defective also on the colour-figure and sound-picture matching test.     

Relative preservation of 'animate' knowledge in an atypical presentation of herpes simplex virus encephalitis

A comprehensive battery of neuropsychological tests designed to assess primary cognitive functions, including language and semantic memory, was given to MG, a patient with confirmed herpes simplex virus encephalitis. MG's initial jargon aphasia resolved over time to leave her with a mild phonological impairment. She had a very mild amnesia that was worse for verbal material and a category-specific impairment of semantic memory. This latter impairment resulted in a significant anomia that was worse for manmade/artefact items than for animate kinds. Her naming difficulties were associated with a mild impairment in comprehension that was not specific to category or feature type. MRI revealed a strongly asymmetric and atypical distribution of pathology in MG with the disease affecting the left medial temporal lobe, temporal pole, left frontotemporal and temporoparietal regions.     

Distinguishing semantic and lexical word retrieval deficits in people with aphasia

Background: Identifying the point of breakdown in people with aphasia with disorders of word retrieval is not straightforward. Evidence has been sought from: (i) the nature of the errors in naming; (ii) the variables affecting naming accuracy; (iii) the effects of correct and misleading cues; (iv) performance in other word comprehension and production tasks. However, previous research has demonstrated that each of these sources of evidence provides information compatible with more than level of breakdown. Aims: The study investigates whether a combination of information from these sources can provide a coherent account of how word retrieval is breaking down in people with aphasia. Methods & Procedures: Three people with aphasia (JGr, LM, and KS) took part in four experiments. The first investigated the errors made in picture naming and the factors (target word length, imageability, frequency …) affecting naming accuracy. The second experiment investigated the effects of correct phonemic cues and miscues on word retrieval. The third examined the participants' performance in tests of spoken and written word and picture comprehension. The fourth experiment investigated whether the participants had the processing abilities necessary to generate their own phonemic cues in spoken naming from orthographic information. Outcomes & Results: Evidence from these investigations showed different levels of breakdown in the three participants. JGr's naming was characterised by semantic errors, effects of target imageability and familiarity on naming accuracy, improved naming with correct phonemic cues and semantic errors with miscues, and poor performance in word comprehension tasks. This pattern is consistent with a breakdown at a semantic level underlying JGr's difficulty in word retrieval. In contrast, LM shows performance indicating a breakdown in mapping between intact semantic and phonological representations. He makes primarily no response errors in naming and his accuracy is affected only by frequency and familiarity. Correct phonemic cues can improve his naming accuracy to near normal levels, and he makes no semantic errors, although he is slowed by miscues. His word and picture comprehension is intact. KS shows a more complex pattern of impairment. Like JGr, she shows evidence of a semantic impairment: she makes semantic errors in naming, and her accuracy is affected by target imageability. She makes errors in word comprehension and her word retrieval is adversely affected by miscues. There are two unusual features to her performance: her naming accuracy is not improved by initial phoneme cues (despite effects of miscues and more extensive phonemic cues), and she is better at naming pictures with longer names (a “reverse length effect”). Investigations in experiment four show that KS is using orthographic information on the initial letter of names to generate her own phonemic cues; it is concluded that in addition to her semantic deficit she has an impairment in access to lexical phonological representations. Conclusions: We conclude that careful investigation of the performance of people with aphasia across a range of tasks can be used to identify underlying levels of breakdown in word retrieval. However, superficial resemblances between people with aphasia can be misleading.     

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.     

Impaired semantic knowledge underlies the reduced verbal short-term storage capacity in Alzheimer's disease

A decrease in verbal short-term memory (STM) capacity is consistently observed in patients with Alzheimer's disease (AD). Although this impairment has been mainly attributed to attentional deficits during encoding and maintenance, the progressive deterioration of semantic knowledge in early stages of AD may also be an important determinant of poor STM performance. The aim of this study was to examine the influence of semantic knowledge on verbal short-term memory storage capacity in normal aging and in AD by exploring the impact of word imageability on STM performance. Sixteen patients suffering from mild AD, 16 healthy elderly subjects and 16 young subjects performed an immediate serial recall task using word lists containing high or low imageability words. All participant groups recalled more high imageability words than low imageability words, but the effect of word imageability on verbal STM was greater in AD patients than in both the young and the elderly control groups. More precisely, AD patients showed a marked decrease in STM performance when presented with lists of low imageability words, whereas recall of high imageability words was relatively well preserved. Furthermore, AD patients displayed an abnormal proportion of phonological errors in the low imageability condition. Overall, these results indicate that the support of semantic knowledge on STM performance was impaired for lists of low imageability words in AD patients. More generally, these findings suggest that the deterioration of semantic knowledge is partly responsible for the poor verbal short-term storage capacity observed in AD.     

Relative preservation of ‘animate’ knowledge in an atypical presentation of herpes simplex virus encephalitis

A comprehensive battery of neuropsychological tests designed to assess primary cognitive functions, including language and semantic memory, was given to MG, a patient with confirmed herpes simplex virus encephalitis. MG’s initial jargon aphasia resolved over time to leave her with a mild phonological impairment. She had a very mild amnesia that was worse for verbal material and a category-specific impairment of semantic memory. This latter impairment resulted in a significant anomia that was worse for manmade/artefact items than for animate kinds. Her naming difficulties were associated with a mild impairment in comprehension that was not specific to category or feature type. MRI revealed a strongly asymmetric and atypical distribution of pathology in MG with the disease affecting the left medial temporal lobe, temporal pole, left frontotemporal and temporoparietal regions.     

Routine clinical diagnosis of primary progressive non-fluent aphasia

It may be difficult to distinguish between a primary progressive aphasia at a very mild stage from the beginning of Alzheimer's disease (AD). However, this may be achieved by carrying out simple neuro-psychological tests. Nine non-fluent PPA (NFPPA) and 76 AD patients with comparable MMSE as well as 58 control subjects were evaluated using simple tests: MMSE, fluency, apraxia, naming, digital span, story memory, 5 words memory test. NFPPA patients had significantly impaired functions during the semantic category fluency and naming tests as compared to AD patients, whereas they showed a better delayed recall of the 5 words and story memory tests. As compared to AD, MMSE of NFPPA patients was also better in the time orientation and word recall sub-tests, although inferior in words repetition and language items. Thus, with comparable MMSE, NFPPA patients have more lexico-semantic difficulties, but a better delayed verbal memory than AD patients. These simple tests easily confirm the language impairment of NFPPA patients as opposed to the mnestic difficulties of AD, even at very early stages of these pathologies.     

Spared numerical abilities in a case of semantic dementia

We report a case study of a patient (IH) with a progressive impairment of semantic memory affecting all categories of knowledge apart from numbers. Pictorial material was better understood than words, but was still severely impaired. The selective preservation of nearly all aspects of numerical knowledge suggested that this domain might have different neuropsychological status from other aspects of semantic memory.     

Word-stem completion task to investigate semantic network in patients with Alzheimer''s disease

Semantic impairment in patients with Alzheimer's disease (AD) is revealed by tasks of verbal naming, verbal fluency, and semantic knowledge. Causes of the deficit remain unclear in spite of many studies to investigate whether AD patients suffer from the inability to have voluntary access to an almost intact semantic store or from its break down. Word-stem completion (WSC) tasks have been utilized in healthy subjects in order to study semantic memory and network by exploiting the possibility of the involuntary access to them. Available conflicting data refer to the presence of semantic prime in AD patients. To explore the semantic network in AD, patients were requested to complete with the first word that sprang to their mind a stem submitted immediately after presentation of the word prime, as a WSC task. Stems consisted of the three beginning letters of words that were semantically related to primes. We compared data obtained with this task from patients with mild to moderate AD with those from normal controls (NC). AD patients completed less stems (P<0.001) with the expected words than NC, suggesting a break down of the semantic network rather than a deficit in the access to the semantic store.     

Relearning and retention of verbal labels in a case of semantic dementia

Background: Previous studies looking at relearning and retention of word labels in people with semantic dementia have shown some improvement in naming immediately after the period of learning but this has not usually been maintained. Studies have also shown rigid learning of names, in the order of presentation and to the picture exemplars only, with no generalisation of learning.

Aims: This study aimed to explore relearning of a small vocabulary set in a person with semantic dementia (CUB) and to examine her ability to generalise this learning. In addition, it aimed to find out how long the learning persisted after therapy was completed given that semantic dementia is a progressive disorder.

Methods & Procedures: A single‐case design was used where CUB was asked to learn 28 words while a further 28 were left as controls. A “look and say” method was used daily for 1 month. As well as examining learning of the therapy and control set, CUB was asked to name 168 other exemplars of the learning set to see whether there had been any transfer of her learning from the therapy set.

Outcomes & Results: CUB not only relearned a set of picture names but retained these without deliberate practice over a 6‐month period. She was also able to generalise this learning to other visually similar exemplars in testing and in daily use. The maintenance of relearning was achieved despite severe deterioration in her semantic memory.

Conclusions: Possible reasons are explored as to why CUB was able to relearn and retain these words and why this may differ from all previously reported cases. Differences in amount of time spent relearning, number of items learned, therapy methods, the severity of semantic memory impairment, the degree of atrophy, and the behavioural profiles of people with semantic dementia do not provide adequate explanations for our individual's differential ability to retain her learning over 6 months. The most plausible explanation is that the person with semantic dementia generalised her learning to her everyday speech and this provided the source of maintenance for the relearned names.     

A category-specific advantage for numbers in verbal short-term memory: evidence from semantic dementia

This study explored possible reasons for the striking difference between digit span and word span in patients with semantic dementia. Immediate serial recall (ISR) of number and non-number words was examined in four patients. For every case, the recall of single-digit numbers was normal whereas the recall of non-number words was impaired relative to controls. This difference extended to multi-digit numbers, and remained even when frequency, imageability, word length, set size and size of semantic category were matched for the numbers and words. The advantage for number words also applied to the patients' reading performance. Previous studies have suggested that semantic memory plays a critical role in verbal short-term memory (STM) and reading: patients with semantic dementia show superior recall and reading of words that are still relatively well known compared to previously known but now semantically degraded words. Additional assessments suggested that this semantic locus was the basis of the patients' category-specific advantage for numbers. Comprehension was considerably better for number than non-number words. Number knowledge may be relatively preserved in semantic dementia because the cortical atrophy underlying the condition typically spares the areas of the parietal lobes thought to be crucial in numerical cognition but involves the inferolateral temporal-lobes known to support general conceptual knowledge.     

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.     

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.     

Verbal learning and forgetting in patients with temporal lobe epilepsy

Studies comparing non-surgical patients with left or right temporal lobe epilepsy (TLE) have shown irregular differences in verbal learning and memory. We assessed the performance of unoperated patients with epileptogenic temporal lobe lesions or cryptogenic TLE using a selective reminding procedure for the learning of a word list, and five delayed trials for the recall of learned words. On the selective reminding procedure, patients with left TLE were found to be more impaired than those with right TLE and controls, in agreement with the role of the left temporal lobe in verbal learning. The patients with right TLE were more impaired than the controls, possibly due to the semantic organization of the word list The rate of forgetting learned words was similar in the patient and control groups, suggesting that patients with left TLE can normally retain and/or retrieve stored items. These data support the hypothesis that distinct functional systems subserve learning and memory. Comparisons of the patient subgroups with epileptogenic lesions (hippocampal sclerosis or low-grade glioma) and those with cryptogenic TLE did not reveal any significant difference in learning or in memory, suggesting that epileptiform activity could affect verbal performance as a detectable temporal lesion.     

No right to speak? The relationship between object naming and semantic impairment: neuropsychological evidence and a computational model

The processes required for object naming were addressed in a study of patients with semantic dementia (a selective decline of semantic memory resulting from progressive temporal lobe atrophy) and in a computational model of single-word production. Although all patients with semantic dementia are impaired in both single-word production and comprehension, previous reports had indicated two different patterns: (a) a parallel decline in accuracy of naming and comprehension, with frequent semantic naming errors, suggesting a purely semantic basis for the anomia and (b) a dramatic progressive anomia without commensurate decline in comprehension, which might suggest a mainly postsemantic source of the anomia. Longitudinal data for 16 patients with semantic dementia reflected these two profiles, but with the following additional important specifications: (1) despite a few relatively extreme versions of one or other profile, the full set of cases formed a continuum in the extent of anomia for a given degree of degraded comprehension; (2) the degree of disparity between these two abilities was associated with relative asymmetry in laterality of atrophy: a parallel decline in the two measures characterized patients with greater right- than left-temporal atrophy, while disproportionate anomia occurred with a predominance of atrophy in the left-temporal lobe. In an implemented computational model of naming, semantic representations were distributed across simulated left- and right-temporal regions, but the semantic units on the left were more strongly connected to left-lateralized phonological representations. Asymmetric damage to semantic units reproduced the longitudinal patient profiles of naming relative to comprehension, plus additional characteristics of the patients' naming performance. On the basis of both the neuropsychological and computational evidence, we propose that semantic impairment alone can account for the full range of word production deficits described here.