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.

Spatial deficits in an amnesic patient with hippocampal damage: questioning the multiple trace theory.

Mediotemporal lobe structures are involved in both spatial processing and long-term memory. Patient M.R. suffers from amnesia, due to bilateral hippocampal lesion and temporoparietal atrophy following carbon monoxide poisoning. We compared his performance in immediate spatial memory tasks with the performance of ten healthy matched participants. Using an immediate reproduction of path, we observed a dissociation between his performance in three allocentric tasks and in five egocentric-updating tasks. His performance was always impaired on tasks requiring the use of an egocentric-updating representation but remained preserved on allocentric tasks. These results fit with the hypothesis that the hippocampus plays a role in spatial memory, but they also suggest that allocentric deficits previously observed in amnesia might actually reflect deficits in egocentric-updating processes. Furthermore, the co-occurrence of deficits in episodic long-term memory and short-term egocentric-updating representation without any short-term allocentric deficit suggests a new link between the mnemonic and navigational roles of the hippocampus. The Cognitive Map theory, the Multiple Trace theory, as well as further models linking spatial and nonspatial functions of the hippocampus are discussed.

Associative visual agnosia: a case study.

We report a case of massive associative visual agnosia. In the light of current theories of identification and semantic knowledge organization, a deficit involving both levels of structural description system and visual semantics must be assumed to explain the case. We suggest, in line with a previous case study, an alternative account in the framework of (non abstractive) episodic models of memory.

[Semantic dementia: reflexions of a French working group for diagnostic criteria and constitution of a patient cohort]. / Démence sémantique: réflexions d'un groupe de travail pour des critères de diagnostic en français et la constitution d'une cohorte de patients.

Semantic dementia (SD) is a syndrome of progressive loss of semantic knowledge for objects and people. International criteria propose that SD be included in the frontotemporal lobar degeneration syndromes, with progressive non-fluent aphasia and frontotemporal dementia (FTD). However, several related syndromes have been defined that clinically and conceptually share both similarities and differences with SD: fluent progressive aphasia, progressive prosopagnosia, temporal variant of FTD. In order to establish a French consensus for the diagnosis and modalities of evaluation and follow-up of SD, a working group, composed of neurologists, neuropsychologists and speech-therapists, was established by the Groupe de réflexion sur les évaluations cognitives (GRECO). New criteria were elaborated, based on clinical, neuropsychological, and imaging data. They define typical and atypical forms of SD. A diagnosis of typical SD relies on an isolated and progressive loss of semantic knowledge, attested by a deficit of word comprehension and a deficit of objects and/or people identification, with imaging showing temporal atrophy and/or hypometabolism. SD is atypical if the deficit of semantic knowledge is present only within a single modality (verbal versus visual), or if non-semantic deficits (mild and not present at onset) and/or neurological signs, are associated with the semantic loss.

Functional MRI assessment of the hemispheric predominance for language in epileptic patients using a simple rhyme detection task.

This study assesses the interest of a simple fMRI rhyme detection paradigm to determine hemispheric predominance for language in epileptic patients. Nineteen patients were examined. The findings derived from the fMRI examinations were compared with those obtained on the same patients using the Wada test, stereotactic intracerebral EEG stimulations and recordings, and/or video-EEG recordings. For the seventeen patients for whom language dominance could be assessed by means of at least one of the latter procedures, the fMRI examination provided concordant results in sixteen. In two patients, the hemispheric predominance for language could only be determined by fMRI. Nine patients underwent surgery subsequent to the fMRI examination. None of them exhibited any aphasic problems following surgery. The rhyme detection task used in the fMRI examination generates robust responses in the language areas, permits easy monitoring of the patient's task performance and can be easily undertaken by the epileptic patients. Thus, this study demonstrates that the fMRI rhyme detection paradigm is particularly well-suited for determining hemispheric language predominance in epileptic candidates for surgery.

Are semantic errors actually semantic?: Evidence from alzheimer's disease.

Patients with Alzheimer's disease (AD) produce a high rate of semantic errors when naming to confrontation. This is considered to be one of the many consequences of their semantic memory deficit. However, it has been shown, in aphasic patients with focal lesions, that semantic errors could arise from impairment to any one of the levels in the naming process. To check this hypothesis in AD, we assessed in 15 patients the capacity to name and access semantic knowledge (by multiple-choice probe questions) about 14 objects presented successively in the visual, tactile, auditory, and verbal modalities. In the visual naming task, 33 errors were recorded: 26 (78.8%) were semantic and 7 (21.2%) were unrelated errors. Of the 26 semantic errors, 8 were related to a deficit of the semantic knowledge related to the item and 17 to a deficit in the retrieval of the phonological form of the word. One was associated with a deficit of access to semantic knowledge in the visual modality. The 7 unrelated errors were associated with a loss of semantic knowledge for 4 and deficit of access to the phonological form for 3. In conclusion, this study shows that semantic errors do not systematically reflect a deficit of semantic knowledge in Alzheimer's disease. It also seems that unrelated errors are more frequently related to semantic deficits than semantic errors in this population.

Identification without manipulation: a study of the relations between object use and semantic memory.

The role of semantic knowledge in object utilisation is a matter of debate. It is usually presumed that access to semantic knowledge is a necessary condition for manipulation, but a few reports challenged this view. The existence of a direct, pre-semantic route from vision to action has been proposed. We report the case of a patient with a disorder of object use in everyday life, in the context of probable Alzheimer's disease. This patient was also impaired when manipulating single objects. He showed a striking dissociation between impairment in object use and preserved capacity to perform symbolic and meaningless gestures. To elucidate the nature of the disorder, and to clarify the relations between semantic knowledge and object use, we systematically assessed his capacity to recognise, name, access semantic knowledge, and use 15 common objects. We found no general semantic impairment for the objects that were not correctly manipulated, and, more importantly, no difference between the semantic knowledge of objects correctly manipulated and objects incorrectly manipulated. These data, although not incompatible with the hypothesis of a direct route for action, are better accommodated by the idea of a distributed semantic memory, where different types of knowledge are represented, as proposed by Allport (Allport, D. A. Current perspectives in dysphasia, pp. 32-60. Churchill Livingstone, Edinburgh, 1985).

One or several semantic system(s)? Maybe none: evidence from a case study of modality and category-specific "semantic" impairment.

Following cerebral anoxia, EC a 55-year-old patient, exhibited a severe and clear-cut pattern of semantic impairments without general intellectual deficit or perceptual difficulty. EC demonstrated a complex neuropsychological picture including a massive visual agnosia and a complete lack of imagery, both of which involved all categories of objects (living and non living) and a category-specific word comprehension deficit limited to animal names. Findings are discussed in the light of the theoretical frameworks currently available in the area of neuropsychology. It is argued that neither the single nor the multiple view of semantics fully succeed in providing a satisfactory account of the data and a tentative interpretation of the whole pattern of impairment is proposed in the general framework of non abstractive conceptions of meaning.

[Deficiency in the reproduction and learning proper names after left tubero-thalamic ischemic lesion]. / Déficit de la production et de l'apprentissage des noms propres après lésion ischémique tubéro-thalamique gauche.

Predominant impairment or preservation of category-specific naming and comprehension is not rare in aphasics. Much less frequent is a selective inability to generate proper names. To our knowledge, only one such case has been reported after a left thalamic lesion, located in the ventral anterior nucleus, the mamillo-thalamic tractus and the genu of the internal capsule. We report a new case of selective inability to generate proper names after a left tubero-thalamic infarct. A 65-year old right-handed man presented with a selective impairment in producing proper names, both from photographs or descriptions and on tests of verbal fluency. The deficit was obvious both for persons names and for geographical names. The rest of the neuropsychological testing was remarkable only for a mild verbal amnesia, affecting only serial material (list of words), a reduced fluency for flowers, fruits and musical instruments, difficulties in learning of new words, and a dissociation between preserved learning for words on a test of learning of words and occupations (Cohen, 1990). This anomia for proper names could result from an indirect frontal-lobe dysfunction, preventing voluntary activation of the phonological representation of proper names.

Right visual hemiagnosia: a single case report.

A patient with an infarct in the territory of the left posterior cerebral artery, but without campimetric deficits presented with some reading difficulties and a visual agnosia restricted to the right visual field. Although the patient was able to match accurately in his agnosic field, he was unable to name or otherwise identify objects. The implications of this case for the anatomical substrates of visual processing and the functions of each hemisphere are discussed.

[Tactile and visual neglect. Preliminary study of 4 patients]. / Négligence tactile et visuelle. Etude préléminaire de quatre patients.

A battery of tactile tests for the study of unilateral neglect is presented with the purpose of comparing the tactile modality to the visual modality. This was applied in 4 patients with right hemisphere lesions. In 3 patients, there was evidence of neglect in both modalities with qualitatively identical anomalies. The function of spatial manipulation involved in the tasks is stressed. In the cases where both modalities were involved a supramodal hemispatial disturbance is assumed.