Specific temporoparietal gyral atrophy reflects the pattern of language dissolution in Alzheimer's disease.
The aim of this study was to determine the topography and degree of atrophy in speech and language-associated cortical gyri in Alzheimer's disease. The post-mortem brains of 10 patients with pathologically confirmed Alzheimer's disease and 21 neurological and neuropathological controls were sectioned in serial 3 mm coronal slices and grey and white matter volumes were determined for specific cortical gyri. All Alzheimer's disease patients had prospectively documented impairments in verbal and semantic memory with concomitant global decline. The cortical regions of interest included the planum temporale, Heschl's gyri, the anterior superior temporal gyri, the middle and inferior temporal gyri, area 37 at the inferior temporoparietal junction, areas 40 and 39 (supramarginal and angular gyri) and Broca's frontal regions. Although most patients had end-stage disease, the language-associated cortical regions were affected to different degrees, with some regions free of atrophy. These included Broca's regions in the frontal lobe and Heschl's gyri on the superior surface of the temporal lobe. In contrast, the inferior temporal and temporoparietal gyri (area 37) were severely reduced in volume. The phonological processing regions in the superior temporal gyri (the planum temporale) were also atrophic in all Alzheimer's disease patients while the anterior superior temporal gyri were only atrophic in female patients. Such atrophy may underlie the more severe language impairments previously described in females with Alzheimer's disease. The present study is the first to analyse the volumes of language-associated gyri in post-mortem patients with confirmed Alzheimer's disease. The results show that atrophy is not global but site-specific. Atrophied gyri appear to reflect a specific network of language and semantic memory dissolution seen in the clinical features of patients with Alzheimer's disease. Females showed greater atrophy than males in the anterior superior temporal gyri. (+info)
"What" and "how": evidence for the dissociation of object knowledge and mechanical problem-solving skills in the human brain.
Patients with profound semantic deterioration resulting from temporal lobe atrophy have been reported to use many real objects appropriately. Does this preserved ability reflect (i) a separate component of the conceptual knowledge system ("action semantics") or (ii) the operation of a system that is independent of conceptual knowledge of specific objects, and rather is responsible for general mechanical problem-solving skills, triggered by object affordances? We contrast the performance of three patients-two with semantic dementia and focal temporal lobe atrophy and the third with corticobasal degeneration and biparietal atrophy-on tests of real object identification and usage, picture-based tests of functional semantic knowledge, and a task requiring selection and use of novel tools. The patient with corticobasal degeneration showed poor novel tool selection and impaired use of real objects, despite near normal semantic knowledge of the same objects' functions. The patients with semantic dementia had the expected deficit in object identification and functional semantics, but achieved flawless and effortless performance on the novel tool task. Their attempts to use this same mechanical problem-solving ability to deduce (sometimes successfully but often incorrectly) the use of the real objects provide no support for the hypothesis of a separate action-semantic system. Although the temporal lobe system clearly is necessary to identify "what" an object is, we suggest that sensory inputs to a parietal "how" system can trigger the use of objects without reference to object-specific conceptual knowledge. (+info)
A problem with auditory processing?
Recent studies have found associations between auditory processing deficits and language disorders such as dyslexia; but whether the former cause the latter, or simply co-occur with them, is still an open question. (+info)
Semantic processing deficits in patients with Parkinson's disease: degraded representation or defective retrieval?
OBJECTIVE: To determine whether degraded representations (characterized by small differences between word sense frequencies), or defective competitive processes (high levels of word sense lateral inhibition), individually or jointly, can give rise to parkinsonian semantic deficits. DESIGN: Computer model of semantic processing. OUTCOME MEASURES: Correct sense selection, defined by the activation of the word sense unit that first reaches the 0.5 activation threshold. If Parkinson disease (PD)-like errors are observed only at high levels of lateral inhibition, independently of low or high sense frequency deltas (SFDs), this would indicate that a defective competitive process alone could account for the errors. Alternatively, if PD-like errors were observed at any level of lateral inhibition, exclusively with low SFD words, this would indicate that degraded representations alone could account for the errors. RESULTS: Neither degraded representations nor defective competitive processes alone can account for parkinsonian semantic errors. An interaction between the 2, however, correctly reproduces both increased errors and longer latency responses. CONCLUSIONS: Competing explanations for semantic deficits in patients with Parkinson's disease need to be integrated in order to develop effective interventions (e.g., estimating the amount of context required to improve semantic processing performance). (+info)
Abnormal angular gyrus asymmetry in schizophrenia.
OBJECTIVE: Few studies have evaluated the parietal lobe in schizophrenia despite the fact that it has an important role in attention, memory, and language-all functions that have been reported to be abnormal in schizophrenia. The inferior parietal lobule, in particular, is of interest because it is not only part of the heteromodal association cortex but also is part of the semantic-lexical network, which also includes the planum temporale. Both the inferior parietal lobule, particularly the angular gyrus of the inferior parietal lobule, and the planum temporale are brain regions that play a critical role as biological substrates of language and thought. The authors compared volume and asymmetry measures of the individual gyri of the parietal lobe by means of magnetic resonance imaging (MRI) scans. METHOD: MRI scans with a 1. 5-Tesla magnet were obtained from 15 male chronic schizophrenic and 15 comparison subjects matched for age, gender, and parental socioeconomic status. RESULTS: Inferior parietal lobule volumes showed a leftward asymmetry (left 7.0% larger than right) in comparison subjects and a reversed asymmetry (left 6.3% smaller than right) in schizophrenic subjects. The angular gyrus accounted for this difference in asymmetry, with the left angular gyrus being significantly larger (18.7%) than the right in comparison subjects, a finding that was not observed in schizophrenic patients. A further test of angular gyrus asymmetry showed a reversal of the normal left-greater-than-right asymmetry in the schizophrenic patients. CONCLUSIONS: Patients with schizophrenia showed a reversed asymmetry in the inferior parietal lobule that was localized to the angular gyrus, a structure belonging to the heteromodal association cortex as well as being part of the semantic-lexical network. This finding contributes to a more comprehensive understanding of the neural substrates of language and thought disorder in schizophrenia. (+info)
Pathological switching between languages after frontal lesions in a bilingual patient.
Cerebral lesions may alter the capability of bilingual subjects to separate their languages and use each language in appropriate contexts. Patients who show pathological mixing intermingle different languages within a single utterance. By contrast, patients affected by pathological switching alternate their languages across different utterances (a self contained segment of speech that stands on its own and conveys its own independent meaning). Cases of pathological mixing have been reported after lesions to the left temporoparietal lobe. By contrast, information on the neural loci involved in pathological switching is scarce. In this paper a description is given for the first time of a patient with a lesion to the left anterior cingulate and to the frontal lobe-also marginally involving the right anterior cingulate area-who presented with pathological switching between languages in the absence of any other linguistic impairment. Thus, unlike pathological mixing that typically occurs in bilingual aphasia, pathological switching may be independent of language mechanisms. (+info)
Neuropsychological consequences of cerebellar tumour resection in children: cerebellar cognitive affective syndrome in a paediatric population.
Acquired cerebellar lesions in adults have been shown to produce impairments in higher function as exemplified by the cerebellar cognitive affective syndrome. It is not yet known whether similar findings occur in children with acquired cerebellar lesions, and whether developmental factors influence their presentation. In studies to date, survivors of childhood cerebellar tumours who demonstrate long-term deficits in cognitive functions have undergone surgery as well as cranial irradiation or methotrexate treatment. Investigation of the effects of the cerebellar lesion independent of the known deleterious effects of these agents is important for understanding the role of the cerebellum in cognitive and affective development and for informing treatment and rehabilitation strategies. If the cerebellar contribution to cognition and affect is significant, then damage in childhood may influence a wide range of psychological processes, both as an immediate consequence and as these processes fail to develop normally later on. In this study we evaluated neuropsychological data in 19 children who underwent resection of cerebellar tumours but who received neither cranial irradiation nor methotrexate chemotherapy. Impairments were noted in executive function, including planning and sequencing, and in visual-spatial function, expressive language, verbal memory and modulation of affect. These deficits were common and in some cases could be dissociated from motor deficits. Lesions of the vermis in particular were associated with dysregulation of affect. Behavioural deficits were more apparent in older than younger children. These results reveal that clinically relevant neuropsychological changes may occur following cerebellar tumour resection in children. Age at the time of surgery and the site of the cerebellar lesion influence the neurobehavioural outcome. The results of the present study indicate that the cerebellar cognitive affective syndrome is evident in children as well as in adults, and they provide further clinical evidence that the cerebellum is an essential node in the distributed neural circuitry subserving higher-order behaviours. (+info)
The cerebellum contributes to higher functions during development: evidence from a series of children surgically treated for posterior fossa tumours.
We present data on the intellectual, language and executive functions of 26 children who had undergone surgery for the removal of cerebellar hemisphere or vermal tumours. The children with right cerebellar tumours presented with disturbances of auditory sequential memory and language processing, whereas those with left cerebellar tumours showed deficits on tests of spatial and visual sequential memory. The vermal lesions led to two profiles: (i) post-surgical mutism, which evolved into speech disorders or language disturbances similar to agrammatism; and (ii) behavioural disturbances ranging from irritability to behaviours reminiscent of autism. These data are consistent with the recently acknowledged role of the cerebellum as a modulator of mental and social functions, and suggest that this role is operative early in childhood. (+info)