语义性痴呆患者语义记忆障碍特征研究

目的探讨语义性痴呆(SD)患者语义记忆障碍的特点,揭示语义记忆的神经解剖机制。方法对9例早期SD患者(病程≤3年)进行详细的神经系统查体、影像学检查和语义记忆评估。语义记忆评估选用常见的动物(生命类)和日常用具(非生命类),统计每一例SD患者对物体名称和功能记忆的正确比例,比较患者对生命类和非生命类物体记忆之间的差异。结果临床上早期SD患者出现广泛的语义记忆损害,所有患者均无感觉或运动方面的症状及体征,颅脑磁共振检查发现所有患者均以左侧颞叶前部萎缩为主,初级感觉皮层和运动皮层正常。所有患者对生命类和非生命类物体的名称及功能均有遗忘,对名称的遗忘更严重。2例患者对生命类物体名称和功能的遗忘较非生命类物体严重,另2例对非生命类物体名称和功能的遗忘重于生命类。结论颞极是语义记忆储存的主要部位,此部位损害后,各种语义记忆普遍受损。语义复合体(名称、知觉和功能)中物体的功能较词语表征更加核心和牢固。部分SD患者存在"语义范畴特异性损害",而且模式并不固定。     

‘Two Eyes of a See-through’: Impaired and Intact Semantic Knowledge in a Case of Selective Deficit for Living Things

Abstract

We report a patient, RC, with a category-specific semantic deficit for living things, who shows the following pattern of behaviour: (1) he has difficulty in distinguishing among individual exemplars for living thing categories, (2) he has no impairment in grouping living things according to their shared properties and (3) in property verification and definition tasks, RC shows good knowledge of shared but not distinctive properties of living things, (especially biological functional properties) and the reverse pattern for non-living things. These findings cannot be accounted for by selective damage to a particular type or category of information. We argue that RC's deficit is predicted by a unitary model of semantic memory in which the patterns of correlation among distinctive and shared perceptual and functional properties are different for concepts in the domains of living and non-living things. These differences in conceptual structure give rise to category-specific impairments when the semantic system is damaged, even when the damage itself is not selective.     

A Longitudinal Study of Category-specific Agnosia

We report a 12-year longitudinal case study on a 60-year-old male patient (DW) with category-specific agnosia. The extent to which DW’s impairment has changed over time was evaluated using identical tests at time 1 (1988) and time 2 (2000). In particular, we assessed his ability to identify pictures and real objects, to draw from memory, and to access stored semantic information about living and non-living things. The principal findings were: (i) DW was significantly better at identifying real objects in comparison with line drawings. (ii) DW presented with a category-specific impairment for living things that remained consistent over the 12-year period. (iii) He significantly improved in his ability to identify real non-living objects over the 12-year period but real living objects remained at floor. (iv) His ability to access stored visual knowledge declined over time. On the basis of these data, we suggest that visual perception is required to maintain intact visual memories over a period of time. We also suggest that integrative visual agnosia co-occurs with a category-specific impairment for living things because the recognition of these items requires more global processing than for non-living things. In addition, we suggest that degradation to stored visual knowledge can cause category-specific naming impairments for living compared with non-living things because naming living things requires access to more detailed visual knowledge.     

Reversed concreteness effect for nouns in a subject with semantic dementia

Selective sparing of abstract relative to concrete words has been documented only exceptionally in aphasia, following bilateral temporal damage. In this paper we present a new case with sparing of abstract word processing and impairment of concrete words due to selective atrophy of the left anterior temporal regions.In our subject, the reversal of the concreteness effect was restricted to nouns. Performance on nouns was not homogeneous. Proper names (people and landmarks) were very severely damaged. Among common names, living entities were selectively impaired in comparison to non-living entities. Category-specific damage for living beings resulted from widespread loss of conceptual information, and perceptual information was less impaired than associative knowledge. This observation challenges theories explaining the reversal of concreteness effect with a selective loss of perceptual information. Also the alternative account, namely a different representational architecture for abstract as opposed to concrete terms, with an advantage for concrete words accruing from an impairment of categorical information, fails to account for the data.Most subjects showing preserved knowledge of abstract words, relative to concrete words, suffer from diseases affecting anterior temporal regions (semantic dementia, herpes encephalitis), and frequently present with greater, or unilateral involvement of the left hemisphere. Our case converges with similar previous reports and with some neuroimaging studies in suggesting that the right temporal lobe and probably the left inferior prefrontal gyrus play a crucial role in the representation of abstract concepts.     

Selective loss of imagery in a case of visual agnosia.

Experiments were designed to examine the imagery abilities of an agnosic patient, M.S., who has consistently shown more severe deficits in recognizing visually, and in retrieving knowledge of living as compared with non-living items. Judgements of visual similarity were required for named objects and for object-pictures, as well as for the factual properties of these stimuli. The same disproportionate difficulty in processing living ('natural') objects was found in these tasks as well as in forced-choice recognition. In contrast, no deficit was found on analogous tasks concerned with word-shape similarities. These findings have a bearing on concepts of semantic memory.     

What the locus of brain lesion tells us about the nature of the cognitive defect underlying category-specific disorders: a review

Different models have been proposed to account for the nature of the cognitive defects underlying category-specific disorders for living and non-living things. One model assumes that the living/non-living distinction is the by-product of a more basic dichotomy, contingent upon the different weighting that visuo-perceptual and functional attributes have in the identification of members of these categories. A second model submits that evolutionary pressure resulted in the elaboration of dedicated neural mechanisms for the domains of living (animals and plants) and non-living (artefacts) things. A third model proposes that the different level of interconnections existing between perceptual and functional features in living and non living things may be more important than the weighting of these features. Each of these models makes implicit assumptions about the extent and the localization of brain lesions provoking category-specific disorders. However, it must also be considered that these disorders are heterogeneous in nature, resulting from defects located at the semantic, lexical or visual level. In the present review of the literature, we kept this distinction in mind in trying to analyze the neuroanatomical correlates of living and non-living disorders. Our findings showed that there is a correlation between the locus of lesion and the patterns of categorical impairment: (a) a bilateral injury to the antero-mesial and inferior parts of the temporal lobes was found in patients with a category-specific semantic impairment for living things; (b) a lesion of the infero-mesial parts of the temporo-occipital areas of the left hemisphere was found in a group of patients showing a specific lexical impairment for members of the 'plants' category; (c) an extensive lesion of the areas lying on the dorso-lateral convexity of the left hemisphere was found in patients with a category-specific semantic impairment for man-made artefacts. Taken together, these results seem to show that the category-specific disorder is crucially related to the kind of semantic information processed by the damaged areas.     

A metanalysis of impaired and spared naming for different categories of knowledge in patients with a visuo-verbal disconnection

The study of the neuroanatomical correlates of category-specific semantic disorders has strongly supported the 'sensory/motor model of semantic knowledge,' which assumes that the cortical areas that have critically contributed to the development of various categories are also implicated in their semantic representation. However, if the anatomo-clinical correlates are consistent with the model, less clearcut results have been obtained by functional neuroimaging experiments. In the present metanalysis, I addressed the question from a different viewpoint, shifting attention from the anatomical lesion in patients with category-specific semantic disorders to the pattern of naming impairment shown by patients suffering from a disconnection between visual areas and lexical output mechanisms. According to the model, living entities should be particularly impaired, since their semantic representations are mainly based upon visual perceptual attributes. On the contrary, actions and body parts (and to a lesser extent artefacts) should be relatively spared, as their semantic representations are mainly based upon motor, somato-sensory or functional attributes. These predictions were checked by reviewing the categorical pattern of naming impairment shown by patients with a visuo-verbal disconnection and a category-specific naming impairment published in the last 20 years. The pattern of impaired and spared categories observed in these patients was consistent with the hypothesis, since: (1) 'actions' and 'body parts' were systematically spared in comparison to all the other categories; (2) 'artefacts' were relatively spared with respect to the 'living categories'; and (3) within the biological categories, 'plants' were usually more impaired than animals.     

A neural basis for category and modality specificity of semantic knowledge.

Prevalent theories hold that semantic memory is organized by sensorimotor modality (e.g., visual knowledge, motor knowledge). While some neuroimaging studies support this idea, it cannot account for the category specific (e.g., living things) knowledge impairments seen in some brain damaged patients that cut across modalities. In this article we test an alternative model of how damage to interactive, modality-specific neural regions might give rise to these categorical impairments. Functional MRI was used to examine a cortical area with a known modality-specific function during the retrieval of visual and non-visual knowledge about living and non-living things. The specific predictions of our model regarding the signal observed in this area were confirmed, supporting the notion that semantic memory is functionally segregated into anatomically discrete, but highly interactive, modality-specific regions.     

A longitudinal study of category-specific agnosia

We report a 12-year longitudinal case study on a 60-year-old male patient (DW) with category-specific agnosia. The extent to which DW's impairment has changed over time was evaluated using identical tests at time 1 (1988) and time 2 (2000). In particular, we assessed his ability to identify pictures and real objects, to draw from memory, and to access stored semantic information about living and non-living things. The principal findings were: (i). DW was significantly better at identifying real objects in comparison with line drawings. (ii). DW presented with a category-specific impairment for living things that remained consistent over the 12-year period. (iii). He significantly improved in his ability to identify real non-living objects over the 12-year period but real living objects remained at floor. (iv). His ability to access stored visual knowledge declined over time. On the basis of these data, we suggest that visual perception is required to maintain intact visual memories over a period of time. We also suggest that integrative visual agnosia co-occurs with a category-specific impairment for living things because the recognition of these items requires more global processing than for non-living things. In addition, we suggest that degradation to stored visual knowledge can cause category-specific naming impairments for living compared with non-living things because naming living things requires access to more detailed visual knowledge.     

Category-specific Naming Impairment for Artefacts: A New Case

Abstract

Most cases of category-specific naming and recognition disorders are characterized by poorer performance with living entities, usually animals. Patients with the less frequently observed opposite pattern of impairment, i.e. better performance with biological entities than with non-living things, provide evidence for a double dissociation, making a strong case for the categorical organization of the semantic system. We describe a patient with a category-specific naming Impairment for tools. GP is a 27-year-old student, evaluated after the evacuation of a haemorrhage in the left temporal lobe. Naming was severely impaired, without significant modality, frequency, word length or grammatical class effects. A significantly inferior performance was present for non-living items (furniture and tools). GP's performance on tests assessing comprehension of the same Items (word-picture matching, forced-choice sentence verification) suggested that semantic knowledge about artefacts he could not name was largely preserved. The localization of the lesion confirms the important role of the left anterior temporal lobe in lexical retrieval.     

Are living and non-living category-specific deficits causally linked to impaired perceptual or associative knowledge? evidence from a category-specific double dissociation

Abstract

Perhaps the most influential view of category-specific deficits is one in which the dissociation between living and non-living kinds reflects differential reliance on, or weighting of visual or associative-functional attributes. We present data collected from two patients, which question the apparent relationship between category-specific deficits and loss of specific attribute types. One patient with dementia of Alzheimer's type presented with relatively poor performance on living things but failed to show a difference between knowledge of visual and associative-functional information. The other patient with semantic dementia demonstrated relatively poor knowledge of visual attributes but failed to exhibit a category-specific impairment for animate kinds. In fact her comprehension and naming were slightly but significantly better for living things. The data are discussed with reference to various theories of category-specific impairment. We suggest that category-specific deficits for living things probably results from a combination of atrophy to medial and neocortical temporal structures, including the inferior temporal lobe. It is proposed that at the behavioural level, category-specific deficits arise when both critical identifying attributes of knowledge are lost and the intercorrelation between features causes disintegration of the category such that each exemplar ‘regresses’ towards a category prototype.     

Intentional and automatic measures of specific-category effect in the semantic impairment of patients with Alzheimer's disease

The breakdown of semantic knowledge relative to living and non-living categories was studied in patients with Alzheimer's disease (AD). The same living and non-living items were used in a semantic battery and in a semantic priming paradigm exploring automatic access to the semantic system. Although AD patients showed a semantic deficit on the intentional semantic battery, they demonstrated normal semantic facilitation on the priming task. In the AD group as a whole, the semantic impairment did not preferentially affect the living category either in the intentional or automatic condition. Instead, a prevalent deficit for the living category was found in three AD patients (14% of the group) on the intentional semantic tasks, but not on the automatic one. These findings support the view that the category effect may not be a generalised phenomenon in AD but may be restricted to a limited number of patients. The intentional/automatic dissociation of the semantic breakdown demonstrated by AD patients is discussed in relation to different theories regarding the organisation of semantic memory.     

The role of noun syntax in spoken word production: Evidence from aphasia

We describe MH who presents with agrammatic aphasia and anomia, and who produces semantic errors in the absence of a central semantic impairment. This pattern of performance implies damage to syntactic processes operating between semantics and phonological output. Damage here may lead to lexical selection errors and a deficit in combining words to form phrases.We investigated MH's knowledge and processing of noun syntax in mass and count nouns. She produced more count nouns than mass nouns. She showed impaired knowledge of noun syntax in judgement tasks and production tasks, with mass noun syntax being more impaired than count.We interpret these results in terms of a two-stage model of lexical retrieval. We propose that syntactic information represented at the lemma level is activated even in bare noun production, and can be differentially impaired across noun categories. That same damage can lead to semantic errors in production. For MH limited syntactic options are available to support production, and these favour count noun production. The data provide a new account of output semantic errors.     

Living musical instruments and inanimate body parts?

In the literature about category effects in semantic memory, body parts and musical instruments are often considered atypical, because in cases with a disproportionate impairment of living categories body parts are relatively spared, while musical instruments are often severely defective. In this study the performance of 57 subjects affected by diseases generally associated with lexical-semantic impairment, for the most part Alzheimer's disease and other forms of cortical degeneration, but also herpetic encephalitis and traumatic brain damage are analyzed. The subjects were given a picture naming task tapping eight categories: three living categories (animals, fruits and vegetables) and three non-living categories (tools, furniture and vehicles), plus body parts and musical instruments. On a preliminary analysis at the group level, body parts were the least impaired category and musical instruments the most severely impaired, the six living and non-living categories being intermediate. However, these differences disappeared after covariance for lexical frequency, name agreement and age of acquisition. The relationship between living categories, non-living categories, musical instruments and body parts was investigated by means of a Lisrel model of Confirmatory Factor Analysis. Two latent variables related to living and non-living categories respectively were defined, and it was found that both body parts and musical instruments were significantly related only with non-living categories. The results showed that the definition of the latent variable expressing the substrate of non-living categories was less satisfactory than that expressing the living categories. On this basis, the conclusions of this study appear statistically definite but their psychological interpretation is less straightforward.     

The Heterogeneity of Category-Specific Semantic Disorders: Evidence from a New Case

We report a new case of category-specific semantic impairment, affecting living entities, in a patient with traumatic brain damage. In the present investigation we attempted to replicate as closely as possible the testing procedures which have been developed by Caramazza and Shelton (1998) to evaluate EW, a patient with a selective semantic disorder for the animal category. The results in our patient indicated a different performance profile, characterised by a more extensive semantic disorder for living entities, and by a more severe loss of specific visual rather than functional knowledge. These findings concur with other evidence indicating that category-specific semantic disorders are heterogeneous, reflecting different mechanisms of impairment, most likely associated with different neurobiological underpinnings.     

The heterogeneity of category-specific semantic disorders: evidence from a new case

We report a new case of category-specific semantic impairment, affecting living entities, in a patient with traumatic brain damage. In the present investigation we attempted to replicate as closely as possible the testing procedures which have been developed by Caramazza and Shelton (1998) to evaluate EW, a patient with a selective semantic disorder for the animal category. The results in our patient indicated a different performance profile, characterised by a more extensive semantic disorder for living entities, and by a more severe loss of specific visual rather than functional knowledge. These findings concur with other evidence indicating that category-specific semantic disorders are heterogeneous, reflecting different mechanisms of impairment, most likely associated with different neurobiological underpinnings.     

Naming tools and animals: asymmetries observed during direct electrical cortical stimulation

Semantically bounded disorders of verbal processing that result in selective dysnomias for items belonging to specific semantic categories have been well documented in lesion studies. Most commonly dissociations between the categories of living versus non-living things have been reported. Processing of living things such as animals seems to be impaired after bilateral lesions, whereas lesions resulting in impairment of processing of non-living things such as tools seem to be restricted to the left hemisphere. In this study, we tested the naming capabilities of epilepsy patients with subdural electrodes implanted for localization of the epileptogenic zone and preoperative mapping of cognitive functions. Tool and animal items were used, and the results show that during stimulation of the left hemisphere dysnomias for tool items were more pronounced than for animal items. This asymmetry is discussed within a model of more widely bilaterally distributed processing of living category members as compared to more restricted left-sided representation of non-living category members.     

Semantic Category Dissociations: A Longitudinal Study of two Cases

We report the neuropsychological findings of two patients (LF and EA) with herpes simplex encephalitis. Both patients presented a greater deficit for living than non-living categories in a number of tasks, although EA was much more impaired than LF. We controlled the several stimulus variables that might affect the performance and could demonstrate that the dissociation was not artifactual. Neither LF nor EA revealed a selective or preferential involvement of perceptual semantic knowledge, and both showed a homogeneous impairment of perceptual and associative encyclopaedic notions. At a second examination, carried out from 1 to 2 years later, LF showed a good recovery, whereas EA's improvement was confined to the non-living categories. The lesion of both patients affected the left temporal pole and the basal neocortical regions of the left temporal lobe. The involvement of limbic areas was more marked in LF, while the Wernicke area and the posterior parts of the middle and inferior temporal gyri were only involved in EA. Besides the basal temporal areas, also the posterior temporal regions are likely to play a role in determining the clinical picture of such patients, and their prospect of recovery.