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Biomedical subjects

M C Silveri

Publications and source records attributed to M C Silveri.

At least 37 records · Page 2Linked to original sources
PubMed1996

Peripheral aspects of writing can be differentially affected by sensorial and attentional defect: evidence from a patient with afferent dysgraphia and case dissociation.

This study reports a patient with right posterior cerebral atrophy who was affected by afferent dysgraphia, characterised by case dissociation: cursive better than upper-case print. The patient also had severe visuocostructional deficit and simultanagnosia. The hypothesis advanced to explain this dissociation is that cases are not equally dependent on visual and kinaesthetic control. Thus, if visual and kinaesthetic feedback (or the attention to them) are impaired by cerebral lesions, upper case can be expected to be more impaired than cursive.

Atrophy↗
PubMed1996

Automatic semantic facilitation in Alzheimer's disease.

To explore the nature of semantic deficit in Alzheimer's disease patients (AD patients) we compared two tasks that are known to be very different with respect to the type of attentional demand and conscious effort they require: lexical decision (automatic) in a semantic priming paradigm and semantic relatedness judgements (intentional). In order to minimise post-lexical facilitation we devised a semantic priming experiment that met an automatic condition as much as possible, and we selected patients without severe word recognition deficits. AD patients showed reduced accuracy in the semantic relatedness judgements as compared to controls. Some effect of priming was found, but this was weaker than in normals. AD patients also differed from controls on targets preceded by a nonlinguistic prime (neutral condition) where their reaction times were slower as compared to neutral condition.

Aged↗
PubMed1995

Hypothesis on the nature of comprehension deficit in a patient with transcortical mixed aphasia with preserved naming.

Patients with poor comprehension and preserved naming have been occasionally described. Such patients, who are affected by transcortical aphasia, have been taken as evidence of the possibility of naming an object while bypassing the semantic system. We describe a patient affected with mixed transcortical aphasia who presented a clear dissociation between ability in naming and difficulties in performing word-picture matching tasks. The pattern is explained by the existence of covert compulsory automatic naming that interferes with less automatic procedures involved in word-picture matching. In fact, when we tried to oppose automatic naming by using, in word-picture matching tasks, pictures difficult to name, the comprehension improved. This finding excludes a semantic deficit at the basis of poor comprehension of our patient. We suggest that the dissociation between naming and comprehension could be an expression of a computational limitation within the processes involved in word-picture matching, due to the competition for limited processing resources by automatically activated hyperactive naming.

Aphasia↗
PubMed1994

Evidence for a possible neuroanatomical basis for lexical processing of nouns and verbs.

Neuropsychological studies have revealed that brain-damaged patients may show impairments of specific word categories. This study reports the performance of three patients with impairments of the categories noun and verb. The first and second patients, with left frontal lobe atrophy, were impaired in naming and comprehension of verbs. The third patient, with striking atrophy of the left temporal lobe, was disproportionately impaired in naming and comprehension of nouns. These findings suggest that anatomically distinct neural systems in the temporal and frontal lobes of the dominant hemisphere might play a critical role in lexical processing of nouns and verbs, respectively.

Aged↗
PubMed1994

Prosopagnosia can be associated with damage confined to the right hemisphere--an MRI and PET study and a review of the literature.

The early position that prosopagnosia is predominantly associated with right hemisphere (RH) injury was challenged by the finding that in practically all cases that come to autopsy pathological data point to bilateral damage. Yet the rejection of the RH hypothesis may have been too hasty. We report three prosopagnosic patients in whom MRI and CT documented a lesion confined to the right occipito-temporal areas and PET confirmed that hypometabolism involved the RH only. A review of the literature brought out 27 cases with neuroimaging evidence that prosopagnosia was associated with RH damage plus four cases with surgical evidence. It remains, however, that the inability to recognize familiar faces is a rare disorder, not manifested by the majority of patients with right temporo-occipital injury. We submit that right-handers differ in the degree of their RH specialization in processing faces and that in only a minority of them is it so marked that it cannot be compensated for by the healthy left hemisphere.

Adult↗
PubMed1994

Disorders of verbal and pictorial memory in right and left brain-damaged patients.

It is still controversial whether verbal and pictorial stimuli are independently processed and stored in memory, as assumed by the dual code hypothesis, or a single code is used both for verbal and for pictorial stimuli, as assumed by the verbal loop hypothesis and by the propositional code hypothesis. According to the first hypothesis, verbal and pictorial memory are independently disrupted by brain damage, whereas according to the second hypothesis a co-occurrence of verbal and pictorial memory disorders are usually observed. To test these contrasting predictions, we constructed a verbal and a pictorial memory task very similar with respect to testing procedures and to material to be memorized and we administered them to 33 left and 27 right brain-damaged patients and to 21 normal controls. The following results were obtained: 1) Disorders of verbal and of pictorial memory were dissociated by brain injury in about one-third of our patients; 2) A consistent relationship was observed between laterality of lesion and type of selective memory impairment, since word recognition was selectively impaired by left and picture recognition by right brain injury; 3) However, only on the test of verbal memory was a significant difference between right and left brain-damaged patients obtained, whereas on the test of pictorial memory only a nonsignificant trend in the opposite direction was observed. These data are in favor of the dual code hypothesis and suggest that the links between left hemisphere and verbal code may be stronger than the relationship between right hemisphere and pictorial code.

Adult↗
PubMed1993

Category-specific deficits for grammatical classes of words: evidence for possible anatomical correlates.

Several neuropsychological studies have shown that brain-damaged patients may demonstrate category-specific deficits for grammatical classes of words, such as nouns and verbs. We describe 3 patients with selective impairments of these latter categories. The first patient, with marked atrophy of the left temporal lobe, was disproportionately impaired in naming and comprehension of nouns. The second patient, with a predominantly left frontal lobe atrophy, was selectively impaired in naming and comprehension of verbs. The third patient, with a left frontal lobe perfusion abnormality, had a selective impairment in naming and comprehension of verbs. Evidence from the present study support the hypothesis that anatomically distinct neural systems in the temporal and frontal lobes of the dominant hemisphere might play a critical role in lexical processing of nouns and verbs respectively.

Aged↗
PubMed1992

Can residual lexical knowledge concern word form rather than word meaning?

We described a patient with a dramatic deficit of both word comprehension and naming but with good preservation of visual pictorial semantics. On word-picture matching, his performances were slightly better than expected based on the observed lexical semantic disorder; in addition, the patient, who maintained good preservation of his underlying phonology, showed a tendency to point to the picture phonologically related to the target. In order to interpret these data, we advanced the hypothesis that the patient, in spite of his virtually complete inability to name, would be able, in a word-picture matching task, to "covertly" (i.e., preverbally) retrieve the name from the picture and to use this name to attempt a match with the phonological form of the stimulus word. This mechanism, that we called "phonological" comprehension, would allow the identification of the correct target and would explain the choice of the phonologically related foil that was sometimes selected.

Aged↗
PubMed1991

Myotonic dystrophy: an electrophysiological study of cognitive deficits.

Patients with Myotonic Dystrophy (MyD) frequently suffer from a dysfunction of the primary sensory pathways, as documented by abnormalities of short-latency evoked potentials. Impairment of intellectual functions has been less extensively investigated. Short-latency brainstem auditory evoked potentials (BAEPs) as well as long-latency auditory event-related potentials (ERPs) were recorded from 5 female and 6 male patients affected by MyD. A simple discrimination ("oddball") paradigm was used to record ERPs to tones from Fz, Cz, Pz. Both BAEPs and ERPs were significantly altered as compared to normals. BAEP abnormalities were detected in 9 patients and ERP components N2 and P3 were delayed or absent for all patients, who nonetheless correctly discriminated between tones. These data indicate that CNS dysfunction in MyD involves not only primary sensory systems but also neural mechanisms underlying cognitive events and ERP generation.

Acoustic Stimulation↗
PubMed1991

Dissociation between knowledge of living and nonliving things in dementia of the Alzheimer type.

Patients who survive herpes simplex encephalitis (HSE) sometimes present a category-specific disorder for living things. Since HSE specifically involves the temporolimbic structures of both hemispheres, these structures could play a critical role in processing and storing information about living things. If this were the case, a category-specific disorder for the same items should also be observed in the early stages of dementia of the Alzheimer type (DAT) as the temporolimbic structures are often severely affected in this condition. To test this hypothesis, we administered to 15 DAT patients and to 10 normal controls a confrontation-naming task and a verbal associates recognition task, with both living and nonliving items as stimuli. The hypothesis was confirmed, since DAT patients performed worse with living than with nonliving items, and scored worse than normal controls on the living but not the nonliving items.

Alzheimer Disease↗
PubMed1989

Variation in the pattern of omissions and substitutions of grammatical morphemes in the spontaneous speech of so-called agrammatic patients.

We describe the patterns of omissions (and substitutions) of freestanding grammatical morphemes and the patterns of substitutions of bound grammatical morphemes in 20 so-called agrammatic patients. Extreme variation was observed in the patterns of omissions and substitutions of grammatical morphemes, both in terms of the distribution of errors for different grammatical morphemes as well as in terms of the distribution of omissions versus substitutions. Results are discussed in the context of current debates concerning the possibility of a theoretically motivated distinction between the clinical categories of agrammatism and paragrammatism and, more generally, concerning the theoretical usefulness of any clinical category. The conclusion is reached that the observed heterogeneity in the production of grammatical morphemes among putatively agrammatic patients renders the clinical category of agrammatism, and by extension all other clinical categories from the classical classification scheme (e.g., Broca's aphasia, Wernicke's aphasia, and so forth) to more recent classificatory attempts (e.g., surface dyslexia, deep dysgraphia, and so forth), theoretically useless.

Adult↗
PubMed1989

The influence of semantic and perceptual factors on lexical comprehension in aphasic and right brain-damaged patients.

We investigated whether the errors made by aphasic patients and right brain-damaged (RBD) patients on a word-picture matching test were differently related to the semantic and perceptual difficulties of the task. To this effect, the target picture was presented in one condition along with two semantically similar distractors, in another condition with two perceptually similar distractors, and in a third condition with two distractors that were both semantically and perceptually similar. There were also two control conditions in which part of targets that had been originally shown with semantic distractors were now presented with perceptual distractors and vice versa. The findings were consistent with the hypothesis that aphasics mainly fail when the task involves semantic discrimination and RBD patients when it involves perceptual discrimination. In aphasics the semantic perceptual condition produced the highest number of errors, but this was due, it was argued, to an increase of the semantic demands of the task.

Analysis of Variance↗
PubMed1986

Molecular forms of cholinesterases in CSF of Alzheimer's disease/senile dementia of Alzheimer type patients and matched neurological controls.

Acetylcholinesterase, pseudocholinesterase and their molecular forms were measured in the CSF of patients affected by Alzheimer's disease and of matched neurological controls. Three different molecular forms of ChE were found in the CSF of both groups of patients, but only two of them belonged to 'true' AChE. No differences were found between Alzheimer's disease patients and neurological controls in all the examined parameters.

Acetylcholinesterase↗
PubMed1986

Anomia with and without lexical comprehension disorders.

Anomic patients are usually described as free from language comprehension disorders, but the status of lexical comprehension in anomia is still controversial. Most anomic patients are impaired on tasks of semantic-lexical discrimination, but some of them do not present clear signs of semantic-lexical deficit at the receptive level. The aim of the present research was to elucidate the nature of word-finding disturbances by contrasting results obtained by anomic patients with and without lexical comprehension disorders on a number of variables, namely severity of anomia, implicit knowledge of words that patients failed to name, presence of verbal-semantic paraphasias, and scores obtained on a test of phoneme discrimination and on the "Token Test." The results of our investigation seem to suggest that there are two types of anomia, caused by the impairment of two different sets of mechanisms. In "purely expressive anomia" the locus of defect seems to be near to the stage in which the selected lexical item is specified into the appropriate phonological form. In "anomia with lexical comprehension disturbances" the locus of defect seems to be much deeper within the lexicon, so that the semantic disorder affects both the expressive and the receptive levels in a roughly comparable manner.

Adult↗
PubMed1986

Disorders of classificatory activity in aphasia.

Two nonverbal tasks of classificatory activity ("class inclusion" and "class intersection") were administered to 46 aphasics, 28 normal controls, 19 nonaphasic left-brain-damaged and 17 right-hemisphere-damaged patients in order to study if aphasic patients are more impaired than nonaphasic brain-damaged patients on these two tasks of elementary logic and if a relationship exists within the aphasic patients between inability to perform the tasks of classifiactory activity and impairment of the semantic-lexical level of integration of language. Results were for the most part in line with expectations because aphasics scored worse than normal controls and nonaphasic brain-damaged patients (even if the difference reached the level of statistical significance only on the test of "class intersection") and within the aphasic patients the worst results were obtained by subjects presenting clear signs of semantic-lexical disintegration.

Aphasia↗
PubMed1986

Mechanisms of unilateral spatial neglect in relation to laterality of cerebral lesions.

An Overlapping Figures test, considered as appropriate to study focusing of attention on small but complex stimuli falling in the central parts of visual field and a Searching for Animals test, designed to study the exploration of large parts of extrapersonal space, were administered to 38 controls, and 90 right and 82 left brain-damaged patients. The investigation was designed to test the hypothesis that the extent of space to be explored may have a different influence on unilateral spatial neglect of right and left brain-damaged patients. Both right and left brain-damaged patients showed an asymmetric exploration of space on the Searching for Animals test, making more omissions on the side contralateral to the damaged hemisphere than on the ipsilateral one. On the Overlapping Figures test, however, only right brain-damaged patients showed a clear tendency to omit figures lying on the left side of the composite pattern. This finding suggests that inability to extract visual information from one side of the stimuli during single eye fixations may be the most characteristic feature of unilateral spatial neglect resulting from right hemisphere lesions.

Attention↗