The cerebellum contributes to linguistic production: a case of agrammatic speech following a right cerebellar lesion

We describe a patient who, after a right cerebellar infarction, developed a right hemicerebellar syndrome and agrammatic speech without other cognitive impairments. We hypothesize that the cerebellum provides the temporal interplay among the neural structures underlying the processes responsible for production of sentences.

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.

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.

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.

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.

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.

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.

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.

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.

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.

On the basis for the agrammatic's difficulty in producing main verbs

Current theories of agrammatism do not provide a clear explanation for the co-occurrence of omission of grammatical markers and main verbs in this disorder. This study tested the hypothesis that the two symptom features have distinct underlying causes. Specifically, that the omission of main verbs in agrammatic speech is caused, at least in part, by a lexical (as opposed to a syntactic) deficit. Agrammatic and anomic aphasics and normal controls were given an object and action naming test. Agrammatic patients showed a marked impairment in naming actions in contrast to anomic aphasics and normal controls who named actions better than objects. The action naming impairment in agrammatic patients was interpreted as evidence for the lexical deficit hypothesis of verb omission in the speech of these patients and as a demonstration that agrammatism is a heterogeneous disorder that implicates damage to both lexical and syntactic mechanisms.

Drawing objects from memory in aphasia

The ability of aphasic patients to draw from memory objects with a characteristic shape has been investigated. Their capacity to reproduce the form of real objects was studied by showing them for a short time line drawings of simple objects. When the patient had analysed and recognized the figure, the model was hidden from view and the subject was asked to draw the same object from memory. This Drawing from Memory task was administered to 54 aphasics, 67 patients with right hemisphere lesions, 44 nonaphasic left brain-damaged patients and 23 normal controls. The influence of visuoconstructive disabilities was controlled by administering to the same patients a standard test for constructional apraxia (copying 10 geometrical figures). The severity and clinical form of the aphasia and the presence of semantic-lexical impairment at the receptive level were also examined in the aphasic patients. The following results were obtained. (1) Aphasic patients scored significantly less well than the control groups on the Drawing from Memory task and the intergroup differences became greater when the scores from the test for constructional apraxia were included by an analysis of covariance. (2) No significant correlation was detected between the severity and clinical form of the aphasia and the scores obtained on the Drawing from Memory task. (3) There was a significant correlation between impaired drawing from memory and disruption at the semantic-lexical level of language integration.

The production of morphological and lexical opposites in aphasia

Four unselected groups of Broca's, Wernicke's, conduction, amnesic aphasic patients and a group of normal controls were asked to produce the best opposite of 60 adjectives. For half of the stimuli the expected opposite was morphologically related to the stimulus word (e.g. "formal"/"informal"), for the other half it could be obtained only by selecting a new base-form within the lexicon (e.g. "good"/"bad"). Following some neurolinguistic observations by Hécaen et al., it was predicted that amnesic patients should produce mainly morphological opposites, whereas conduction aphasics should produce mainly lexical antonyms. Results confirmed the predictions, since amnesic aphasics showed a prevalent impairment in the selection lexical opposites, whereas conduction aphasics showed a selective impairment in the production of morphological antonyms.

Influence of age, sex, literacy and pathologic lesion on incidence, severity and type of aphasia

The influence of sex, age, educational level and pathologic lesion on incidence, severity and clinical form of aphasia was investigated in 390 right-handed, left brain-damaged patients. Sex and educational level were not related to any parameter. Etiology of lesion and age were related to both incidence and type of aphasia. Incidence of aphasia increased with age and was higher in patients with cerebrovascular accidents than in subjects with other types of brain lesions. Non-fluent forms of aphasia were more frequent in young patients suffering from acute cerebrovascular accidents, whereas anomia prevailed in neoplastic subjects and Wernicke's aphasia increased regularly in frequency with age. Some tentative explanations of these findings are discussed.

The relationship between type of naming error and semantic-lexical discrimination in aphasic patients

When submitted to confrontation naming tasks, aphasic patients show different types of naming errors: phonetic, phonemic and verbal-semantic paraphasias, neologisms and anomia, but it is generally difficult to decide whether these errors are mainly due to a breakdown of the semantic systems or to post-lexical phonological disorders. In order to clarify this issue, 118 aphasic patients were given 3 tests of confrontation naming and 3 tests of semantic-lexical discrimination. Naming errors on confrontation were used to classify aphasic patients in various subgroups (according to the prevalence of a given type of naming error), whereas performances obtained on tests of semantic-lexical discrimination were taken as an index of disorganization of the semantic systems. The performances on semantic discrimination tests of patients showing a prevalence of phonetic, phonemic and verbal-semantic paraphasias, neologisms and anomia on confrontation naming tasks were compared. A very small number of semantic discrimination errors was obtained by patients showing a prevalence of phonetic and phonemic transformations on confrontation, whereas a much larger number of semantic discrimination errors was obtained by patients showing a prevalence of verbal-semantic paraphasias, neologisms and anomia.

Neuropsychological correlates of localized cerebral lesions in non-aphasic brain-damaged patients

A neuropsychological test battery made up of verbal, visual-spatial, and intelligence tests was administered to 82 right and 67 on-aphasic left brain-damaged patients with localized cerebral lesions, in order to draw impairment profiles of the various subgroups. Separate analyses were undertaken on patients with unilobar and multilobar lesions. As for hemisphere effects, LH patients performed worse than RH subjects on verbal tests, while the reverse was true for visual-spatial tasks. As for lobe effects, patients with frontal lobe damage fared worse than other subgroups on word fluency, independent of the side of the lesion. RH patients with multilobar posterior lesions were significantly more impaired than other RH subgroups on the test of Copying Drawings with Landmarks, probably owing to the detrimental effect of unilateral spatial neglect on tasks requiring an accurate visual-spatial analysis.