Mechanisms of recovery from aphasia: evidence from positron emission tomography studies.
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OBJECTIVES: Language functions comprise a distributed neural system, largely lateralised to the left cerebral hemisphere. Late recovery from aphasia after a focal lesion, other than by behavioural strategies, has been attributed to one of two changes at a systems level: a laterality shift, with mirror region cortex in the contralateral cortex assuming the function(s) of the damaged region; or a partial lesion effect, with recovery of perilesional tissue to support impaired language functions. Functional neuroimaging with PET allows direct observations of brain functions at systems level. This study used PET to compare regional brain activations in response to a word retrieval task in normal subjects and in aphasic patients who had shown at least some recovery and were able to attempt the task. Emphasis has been placed on single subject analysis of the results as there is no reason to assume that the mechanisms of recovery are necessarily uniform among aphasic patients. METHODS: Six right handed aphasic patients, each with a left cerebral hemispheric lesion (five strokes and one glioma), were studied. Criteria for inclusion were symptomatic or formal test evidence of at least some recovery and an ability to attempt word retrieval in response to heard word cues. Each patient underwent 12 PET scans using oxygen-15 labelled water (H2(15)O) as tracer to index regional cerebral blood flow (rCBF). The task, repeated six times, required the patient to think of verbs appropriate to different lists of heard noun cues. The six scans obtained during word retrieval were contrasted with six made while the subject was "at rest". The patients' individual results were compared with those of nine right handed normal volunteers undergoing the same activation study. The data were analysed using statistical parametric mapping (SPM96, Wellcome Department of Cognitive Neurology, London, UK). RESULTS: Perception of the noun cues would be expected to result in bilateral dorsolateral temporal cortical activations, but as the rate of presentation was only four per minute the auditory perceptual activations were not evident in all people. Anterior cingulate, medial premotor (supplementary speech area) and dorsolateral frontal activations were evident in all normal subjects and patients. There were limited right dorsolateral frontal activations in three of the six patients, but a similar pattern was also found in four of the nine normal subjects. In the left inferolateral temporal cortex, activation was found for the normal subjects and five of the six patients, including two of the three subjects with lesions involving the left temporal lobe. The only patient who showed subthreshold activation in the left inferolateral temporal activation had a very high error rate when performing the verb retrieval task. CONCLUSIONS: The normal subjects showed a left lateralised inferolateral temporal activation, reflecting retrieval of words appropriate in meaning to the cue from the semantic system. Lateralisation of frontal activations to the left was only relative, with right prefrontal involvement in half of the normal subjects. Frontal activations are associated with parallel psychological processes involved in word retrieval, including task initiation, short term (working) memory for the cue and responses, and prearticulatory processes (even though no overt articulation was required). There was little evidence of a laterality shift of word retrieval functions to the right temporal lobe after a left hemispheric lesion. In particular, left inferolateral temporal activation was seen in all patients except one, and he proved to be very inefficient at the task. The results provide indirect evidence that even limited salvage of peri-infarct tissue with acute stroke treatments will have an important impact on the rehabilitation of cognitive functions. (+info)
Global aphasia without hemiparesis: language profiles and lesion distribution.
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OBJECTIVES: Global aphasia without hemiparesis (GAWH) is an uncommon stroke syndrome involving receptive and expressive language impairment, without the hemiparesis typically manifested by patients with global aphasia after large left perisylvian lesions. A few cases of GAWH have been reported with conflicting conclusions regarding pathogenesis, lesion localisation, and recovery. The current study was conducted to attempt to clarify these issues. METHODS: Ten cases of GAWH were prospectively studied with language profiles and lesion analysis; five patients had multiple lesions, four patients had a single lesion, and one had a subarachnoid haemorrhage. Eight patients met criteria for cardioembolic ischaemic stroke. RESULTS: Cluster analysis based on acute language profiles disclosed three subtypes of patients with GAWH; these clusters persisted on follow up language assessment. Each cluster evolved into a different aphasia subtype: persistent GAWH, Wernicke's aphasia, or transcortical motor aphasia (TCM). Composite lesion analysis showed that persistent GAWH was related to lesioning of the left superior temporal gyrus. Patients with acute GAWH who evolved into TCM type aphasia had common lesioning of the left inferior frontal gyrus and adjacent subcortical white matter. Patients with acute GAWH who evolved into Wernicke's type aphasia were characterised by lesioning of the left precentral and postcentral gyri. Recovery of language was poor in all but one patient. CONCLUSIONS: Although patients with acute GAWH are similar on neurological examination, they are heterogeneous with respect to early aphasia profile, language recovery, and lesion profile. (+info)
Conduction aphasia elicited by stimulation of the left posterior superior temporal gyrus.
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OBJECTIVE: Disruption of fascicular tracts that connect Wernicke's to Broca's areas is the classic mechanism of conduction aphasia. Later work has emphasised cortical mechanisms. METHODS: To determine the distribution of language on dominant cortex, electrical cortical stimulation was performed using implanted subdural electrodes during brain mapping before epilepsy surgery. RESULTS: A transient, isolated deficit in repetition was elicited with stimulation of the posterior portion of the dominant superior temporal gyrus. CONCLUSION: This finding suggests that cortical dysfunction, not just white matter disruption, can induce conduction aphasia. (+info)
Aphasic disorder in patients with closed head injury.
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Quantitative assessment of 50 patients with closed head injury disclosed that anomic errors and word finding difficulty were prominent sequelae as nearly half of the series had defective scores on tests of naming and/or word association. Aphasic disturbance was associated with severity of brain injury as reflected by prolonged coma and injury of the brain stem. (+info)
Impaired dexterity of the ipsilateral hand after stroke and the relationship to cognitive deficit.
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BACKGROUND AND PURPOSE: Previous research has reported impaired hand function on the "unaffected" side after stroke, but its incidence, origins, and impact on rehabilitation remain unclear. This study investigated whether impairment of ipsilateral dexterity is common early after middle cerebral artery stroke and explored the relationship to cognitive deficit. METHODS: Thirty patients within 1 month of an infarct involving the parietal or posterior frontal lobe (15 left and 15 right hemisphere) used the ipsilateral hand in tests that simulated everyday hand functions. Performance was compared with that of healthy age-matched controls using the same hand. Standardized tests were used to assess apraxia, visuospatial ability, and aphasia. RESULTS: All patients were able to complete the dexterity tests, but video analysis showed that performance was slow and clumsy compared with that of controls (P<0.001). Impairment was most severe after left hemisphere damage, and apraxia was a strong correlate of increased dexterity errors (P<0.01), whereas reduced ipsilateral grip strength correlated with slowing (P<0.05). The pattern of performance was different for patients with right hemisphere damage. Here there was no correlation between grip strength and slowing, while dexterity errors appeared to be due to visuospatial problems. CONCLUSIONS: Subtle impairments in dexterity of the ipsilateral hand are common within 1 month of stroke. Ipsilateral sensorimotor losses may contribute to these impairments, but the major factor appears to be the presence of cognitive deficits affecting perception and control of action. The nature of these deficits varies with side of brain damage. The effect of impaired dexterity on functional outcome is not yet known. (+info)
Language related brain potentials in patients with cortical and subcortical left hemisphere lesions.
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The role of the basal ganglia in language processing is currently a matter of discussion. Therefore, patients with left frontal cortical and subcortical lesions involving the basal ganglia as well as normal controls were tested in a language comprehension paradigm. Semantically incorrect, syntactically incorrect and correct sentences were presented auditorily. Subjects were required to listen to the sentences and to judge whether the sentence heard was correct or not. Event-related potentials and reaction times were recorded while subjects heard the sentences. Three different components correlated with different language processes were considered: the so-called N400 assumed to reflect processes of semantic integration; the early left anterior negativity hypothesized to reflect processes of initial syntactic structure building; and a late positivity (P600) taken to reflect second-pass processes including re-analysis and repair. Normal participants showed the expected N400 component for semantically incorrect sentences and an early anterior negativity followed by a P600 for syntactically incorrect sentences. Patients with left frontal cortical lesions displayed an attenuated N400 component in the semantic condition. In the syntactic condition only a late positivity was observed. Patients with lesions of the basal ganglia, in contrast, showed an N400 to semantic violations and an early anterior negativity as well as a P600 to syntactic violations, comparable to normal controls. Under the assumption that the early anterior negativity reflects automatic first-pass parsing processes and the P600 component more controlled second-pass parsing processes, the present results suggest that the left frontal cortex might support early parsing processes, and that specific regions of the basal ganglia, in contrast, may not be crucial for early parsing processes during sentence comprehension. (+info)
Improving outcomes for persons with aphasia in advanced community-based treatment programs.
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BACKGROUND AND PURPOSE: Studies have yet to document that community-based aphasia treatment programs routinely produce results comparable or superior to published research protocols. We explore this issue here in an outcome study of individuals with aphasia enrolled in 2 community-based, comparably managed and equipped therapy programs, which use a specially designed computer-based tool that is employed therapeutically in adherence to an extensive, detailed, and formally trained patient care algorithm. METHODS: Patients (n=60) were assessed before and after treatment with standardized instruments at both the impairment and the disability levels. Pretreatment and posttreatment means were calculated and compared, with statistical significance of differences established with the use of 1-tailed matched t tests. One-way ANOVAs were used to analyze the comparability of patient performance changes among various subgroups, eg, patients in acute versus chronic stages of aphasia, patients by aphasia diagnostic type at start of care, patients by severity level at start of care, and patients by treatment location. RESULTS: Analysis shows that patients spanned a wide range of aphasia diagnostic types, impairment severity levels at start of care, and times after onset. Patients' mean performance scores improved significantly in response to treatment in all measures assessed at both the impairment level and the functional communication level. Mean overall improvements ranged from 6.6% to 19.8%, with statistical significance ranging from P=0.0006 to P<0.0001. ANOVAs revealed no significant differences between improvements in patients in the acute versus chronic stages of aphasia, between those at different impairment severity levels at start of care, between those treated at different locations, or, at the functional level, between those with different diagnostic types of aphasia at start of care. CONCLUSIONS: Measures of both language impairment and functional communication can be broadly, positively, and significantly influenced by therapy services that are delivered to persons with aphasia in these community-based programs. The significant improvements are shown to be available to individuals with chronic as well as acute aphasia and independent of diagnostic type of aphasia, impairment severity at start of care, or geographic program location. (+info)
Poststroke depression correlates with cognitive impairment and neurological deficits.
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BACKGROUND AND PURPOSE: The prevalence of poststroke depression is known to be high, but the knowledge of its neuropsychological correlates is limited. This 12-month prospective study was designed to evaluate the natural history of poststroke depression and to study its neuropsychological, clinical, and functional associates. METHODS: We studied a series of 106 consecutive patients (46 women and 60 men, mean age 65.8 years) with acute first-ever ischemic stroke. The patients underwent a neurological, psychiatric, and neuropsychological examination at 3 and 12 months after the stroke. The psychiatric diagnosis of depression was based on DSM-III-R-criteria. RESULTS: Depression was diagnosed in 53% of the patients at 3 months and in 42% of the patients at 12 months after the stroke. The prevalence of major depression was 9% at 3 months and 16% at 12 months. There was an association between poststroke depression and cognitive impairment; the domains most likely to be defective in stroke-related depression were memory (P=0.022), nonverbal problem solving (P=0.039), and attention and psychomotor speed (P=0.020). The presence of dysphasia increased the risk of major depression. The depressive patients were more dependent in ADL and had more severe impairment and handicap than the nondepressive patients. CONCLUSIONS: More than half of the patients suffer from depression after stroke, and the frequency of major depression seems to increase during the first year. In addition to dysphasia, poststroke depression is correlated with other cognitive deficits. We emphasize the importance of psychiatric evaluation of stroke patients. (+info)