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Biomedical subjects

J L Signoret

Publications and source records attributed to J L Signoret.

At least 37 records · Page 2Linked to original sources
PubMed1989

[Cerebral evoked potentials and conscious and unconscious recognition of faces: application to the study of prosopagnosia].

Twelve normal subjects and a prosopagnosic patient were tested in a classification task of a random display of well-known among unknown faces. Each face was presented several times. Event-related potentials (ERP) and reaction time (RT) were studied as a function of face repetition and familiarity. For normal subjects, the greater the repetition level, the more positive ERPs were on both hemispheres: between 250 and 600 msec. Moreover, the familiarity of faces modified ERPs between 350 and 600 msec. In contrast for the patient, the greater the repetition, the more negative the ERPs were. This "negative effect" was maximum on right parieto-temporal leads and was longer for unrecognized well-known than for unknown faces. These results support a differential processing of faces as a function of their memory representations for both normal subjects and patients. They further demonstrate the existence of covert face recognition processes in prosopagnosia.

Adult↗
PubMed1989

[Are the lesions responsible for prosopagnosia always bilateral?].

To localize the lesions responsible for prosopagnosia one must first consider how recent anatomico-physiological data have modified our view of the visual system: the visual cortex has been parceled into a mosaic of visual areas, each of them processing preferentially a particular feature (form, colour, movement); there is evidence of a face area in the monkey temporal lobe, and a new model of the inferior longitudinal fasciculus has been offered. It is currently accepted that face recognition deficits are due to bilateral occipito-temporal lesions, but in view of several recent reports in which the lesions were localized on CT or MRI one may doubt that these lesions are necessarily bilateral. In some cases a right unilateral lesion seemed to be sufficient to induce prosopagnosia.

Agnosia↗
PubMed1989

[Visual object agnosia: current conceptions].

Visual agnosia for objects is a difficulty in recognizing objects presented visually. This difficulty can not be explained by a mental deterioration, a disorder of attention or a lack of familiarity with the object. Two criteria are essential but disputed: the absence of visual sensory difficulty necessary for adequate perception; possible recognition of the object by another sensory modality. An object is characterized by a triple representation: formal, semantic, lexical. The clinical, cognitive, pathophysiological analysis lead to distinguish 3 types of visual agnosia. 1) Aperceptive visual agnosia: patients see badly with morphological errors; the disorder concerns visual informations processing that is a necessary condition for identifying the formal representation of the object; the lesions are bilateral and involve the occipito-temporal cortex. 2) Associative visual agnosia: patients can copy, are not aphasic, but give erroneous verbal responses; the disorder concerns the links between formal representations and semantic, lexical representations; the lesions are unilateral and involve the left gyrus angularis connections. 3) Asemantic visual agnosia: patients have lost the meanings of objects and words; the disorder concerns semantic representations; the lesions are bilateral and involve the temporo-limbic cortex.

Agnosia↗
PubMed1987

[Aphasia without amusia in a blind organist. Verbal alexia-agraphia without musical alexia-agraphia in braille].

A 77 year old right handed male was blind since the age of 2. He presented with an infarction involving the territory of the left middle cerebral artery involving the temporal and the inferior parietal lobes. He had learned to read and write language as well as read and write music in braille, ultimately becoming a famous organist and composer. There were no motor or sensory deficits. Wernicke's aphasia with jargonaphasia, major difficulty in repetition, anomia and a significant comprehension deficit without word deafness was present; verbal alexia and agraphia in braille were also present. There was no evidence of amusia. He could execute in an exemplary fashion pieces of music for the organ in his repertory as well as improvise. All his musical capabilities: transposition, modulation, harmony, rythm, were preserved. The musical notation in braille remained intact: he could read by touch and play unfamiliar scores, he could also read and sing the musical notes, he could copy and write a score. Nine months after the stroke his aphasia remained unchanged. Nevertheless he composed pieces for the organ which were published. Such data highly suggest the independence of linguistic and musical competences, defined as the analysis and organization of sounds according to the rules of music. This independence in an extremely talented musician leads to a discussion of the role of the right hemisphere in the anatomical-functional processes at the origin of musical competence. The use of braille in which the same constellations of dots correspond either to letters of the alphabet or musical notes supports the independence between language and music.

Aged↗
PubMed1986

[Myoclonic cerebellar dyssynergia (Ramsay-Hunt syndrome) and cerebellar telangiectasia].

A 8 year-old girl presented with generalized epileptic seizures followed by the progressive onset of myoclonic jerks, sometimes associated with willed movements, and a static and kinetic cerebellar syndrome without conspicuous intellectual impairment. Death occurred 10 years after the onset of the disorders. There was no family history. Neuropathological studies showed lesions confined to the cerebellum. Diffuse and bilateral telangiectases were present in the cerebellar white matter. They were associated with patchy cortical alterations of the distal parts of some folia involving mainly the granule-cells ans sparing the Purkinje cells. No Lafora bodies and no abnormal lipofuscin storage were observed. The dentate nuclei, superior cerebellar peduncles and red nuclei were normal as were the inferior olives and inferior cerebellar peduncles. The spino-cerebellar tracts were unaffected. This case confirms the hypothesis that dyssynergia cerebellaris myoclonica corresponds only to a clinical entity. It may be encountered in various degenerative or metabolic disorders involving the cerebellum and/or its pathways. To our knowledge the association of a Ramsay Hunt syndrome with a vascular malformation has not been previously reported.

Adolescent↗
PubMed1986

[Memory disorders in lesions of the thalamus in man].

Isolated memory disorders occur after bilateral involvement of thalamus. Anterograde amnesia is not complete; retrograde amnesia is always severe. Four groups of thalamic nuclei may be affected: anterior nuclei; midline nuclei, medialis dorsalis nuclei; intralaminar nuclei. A pathophysiologic interpretation is proposed. Three kinds of memory processes may be involved: consolidating process that leads to the formation of memory traces (anterior nuclei, midline nuclei); retrieving process that leads to the activation of memory traces (intralaminar nuclei); temporal organizing process that regards ancient et recent memory traces (medialis dorsalis nuclei).

Amnesia↗
PubMed1983

[Neuropsychological analysis of Alzheimer's disease].

Neuropsychological analysis, which aims at establishing correlations between mental disorders and alterations in one or several functional cerebral structures, cannot be performed at the dementia stage of Alzheimer's disease. From the nature and variety of the mental disorders observed it may be hypothesized that the disease does not involve one single biochemical system (cholinergic theory) but several systems of neurotransmitters, each of which plays a specific role in man's mental activities.

Aged↗
PubMed1983

[Contribution of the right hemisphere to language in aphasic patients. Disappearance of this language after a right-sided lesion].

Assessments vary as to the contribution of the right hemisphere to language in aphasic patients. Results of a clinicopathologic study in two right-handed subjects with aphasia are reported. The lesions involved the territories of the left middle and anterior cerebral arteries. Oral productions in one case, studied during the three weeks of survival, were limited to automatic series, recitation of a fable, and completion of sentences. Follow-up in the other case was possible during 2 years of language rehabilitation. At the end of this period, repetition of an echolalic type was possible; a propositional expression had appeared, reduced to substantives and verb infinitives; denomination was possible but rich in semantic paraphasias. A second infarction in the right sylvian region caused the recovered language to disappear and to be replaced by an abolition of all communication. Proof was thus obtained that the progress accomplished was dependent on the right hemisphere. These findings are discussed in the light of observations of patients following left hemispherectomy and of the capacity of the right hemisphere to generate language as demonstrated in patients after commissurotomy. A dynamic interpretation of the taking over of expression by the right hemisphere during some aphasias is proposed.

Aphasia↗
PubMed1982

[Creation of Charcot's chair].

A decree signed by the President of the French Republic on the 2nd of January 1882 provided for the creation of the first chair in the world for the teaching of neurology at the Faculty of medicine in Paris. The chair was named: Clinic for Diseases of the Nervous System and was attributed to J. M. Charcot. The historical and political circumstances related to the creation of this chair are reviewed. J. M. Charcot's hospital and university careers are retraced, emphasis being placed on the turning point in 1867 when J. M. Charcot, having been refused the chair of Medical Pathology, dedicated his time to the study of hysteria and nervous system diseases. The birth of neurology is therefore situated in relation to that of psychiatry. But this chair is also and still that of Charcot; it was thus convenient to remind the man, his origins, his personality, his ideas, and his social role.

History, 19th Century↗
PubMed1982

[New approaches to the study of memory impairment in epileptics].

Some memory functions were evaluated in 56 adult epileptic patients. A memory battery scale with verbal and visual material was used. Patients' scores were statistically worse than those of controls matched according for age and cultural level. No differences were observed between generalized and complex partial epilepsies. Left interictal E.E.G. abnormalities were correlated with verbal efficiency impairment. Length of illness and seizure frequency were consistently correlated with poor memory ability. Surprisingly antiepileptic drugs were not a major factors. However, none of these parameters if considered alone accounts for this impairment, which is obviously multifactorial. These poor memory performances are mainly due to a learning decrement. Epileptic patients have difficulties to learn but they well remember what they have learnt.

Child↗