Mechanisms of early aphasia recovery

Background: The course of recovery of aphasia after stroke is highly variable. Some patients, even with severe aphasia, recover rapidly over the first days after onset. The mechanism of this early recovery (and later recovery) is unclear. Plausible accounts include reperfusion of ischaemic tissue surrounding the stroke, and rapid reorganisation of structure/function relationships. Aims: Based on a recent study showing that the severity of word comprehension impairment in acute stroke patients is strongly correlated with the severity of hypoperfusion (low blood flow) in Wernicke's area, we hypothesised that early recovery of spoken word comprehension is due to reperfusion (restored blood flow) to Wernicke's area. Our objective was to evluate this hypothesis using advanced magnetic resonance imaging techniques of perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI). Methods and Procedures: A series of 100 patients with acute, left hemisphere ischaemic stroke were evaluated within 24 hours of onset or worsening of symptoms, and 3 days later, using PWI, DWI, and a battery of lexical tasks, including spoken word/picture verification. A subset of 18 patients with impaired spoken word comprehension at Day 1 were included in the study. Chi square analysis was used to identify the association between early recovery of spoken word comprehension and reperfusion of each of 10 Brodmann's areas (BA). Outcomes & Results: Early recovery of spoken word comprehension was significantly associated with reperfusion of BA 22 (Wernicke's area), but not with reperfusion of other BAs. All patients who showed early recovery of word comprehension also showed reperfusion of Wernicke's area, due to carotid endarterectomy, carotid stenting, induced blood pressure elevation, or spontaneous reperfusion. Conclusions: Tissue recovery, brought about by restored blood pressure elevation, likely accounts for cases of rapid resolution of aphasia in the first few days of stroke. Other mechanisms of recovery, including reorganisation of structure/function relationships, and learning of compensatory strategies, are likely important in later stages of recovery.     

Mechanisms of recovery from aphasia: evidence from positron emission tomography studies

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.     

Recent developments in functional and structural imaging of aphasia recovery after stroke

BACKGROUND: Functional and structural neuroimaging techniques can increase our knowledge about the neural processes underlying recovery from post-stroke language impairments (aphasia). AIMS: In the present review we highlight recent developments in neuroimaging research of aphasia recovery. MAIN CONTRIBUTION: We review (a) cross-sectional findings in aphasia with regard to local brain functions and functional connectivity, (b) structural and functional imaging findings using longitudinal (intervention) paradigms, (c) new adjunct treatments that are guided by functional imaging techniques (e.g., electrical brain stimulation) and (d) studies related to the prognosis of language recovery and treatment responsiveness after stroke. CONCLUSIONS: More recent developments in data acquisition and analysis foster better understanding and more realistic modelling of the neural substrates of language recovery after stroke. Moreover, the combination of different neuroimaging protocols can provide converging evidence for neuroplastic brain remodelling during spontaneous and treatment-induced recovery. Researchers are also beginning to use sophisticated imaging analyses to improve accuracy of prognosis, which may eventually improve patient care by allowing for more efficient treatment planning. Brain stimulation techniques offer a new and exciting way to improve the recovery potential after stroke.     

Recent developments in functional and structural imaging of aphasia recovery after stroke

ABSTRACT

Background: Functional and structural neuroimaging techniques can increase our knowledge about the neural processes underlying recovery from post-stroke language impairments (aphasia).

Aims: In the present review we highlight recent developments in neuroimaging research of aphasia recovery.

Main Contribution: We review (a) cross-sectional findings in aphasia with regard to local brain functions and functional connectivity, (b) structural and functional imaging findings using longitudinal (intervention) paradigms, (c) new adjunct treatments that are guided by functional imaging techniques (e.g., electrical brain stimulation) and (d) studies related to the prognosis of language recovery and treatment responsiveness after stroke.

Conclusions: More recent developments in data acquisition and analysis foster better understanding and more realistic modelling of the neural substrates of language recovery after stroke. Moreover, the combination of different neuroimaging protocols can provide converging evidence for neuroplastic brain remodelling during spontaneous and treatment-induced recovery. Researchers are also beginning to use sophisticated imaging analyses to improve accuracy of prognosis, which may eventually improve patient care by allowing for more efficient treatment planning. Brain stimulation techniques offer a new and exciting way to improve the recovery potential after stroke.     

Mechanisms of motor recovery after cerebrovascular accident]

Recovery from motor deficit after a stroke remains a puzzling scientific question as well as public health problem. The natural history of deficits after stroke is given to us through published series of patients and we know from them that neurological deficits, spontaneously but most of the time partially, recover. Neuroimaging modern techniques (PET scan, fMRI, evoked potentials) allowed us to identify the main aspects of the post-stroke intracerebral reorganisation. Reorganisation of basal cerebral metabolism, changes in the somatotopia of primary motor cortex, recruitment of remote cortices, participation of associative cortices are clearly part of the rearrangement processes. It is likely that such mechanisms represent the basis of clinical recovery of our patients. However, despite those important advances, very few is known about the effect of treatments on the recovery phenomenon. Some lines of evidence appear now to give rationale to rehabilitation procedures and to drugs suspected to improve clinical recovery.     

Neuroimaging of recovery from aphasia

This paper is a selective review of neuroimaging studies about recovery from aphasia. Two basic mechanisms, i.e., regression of diaschisis and functional reorganisation, have been considered to play an important role in language recovery. The results of recent investigations using positron emission tomography and other functional imaging modalities are reviewed, from the point of view of their contribution to the understanding of the respective role of these mechanisms. Finally, an integration is attempted between these findings and general theories of functional recovery, underlining the crucial role of the spared areas in the language-dominant hemisphere, and the limits to brain plasticity in the adult brain.     

Mechanisms of recovery from aphasia: evidence from serial xenon 133 cerebral blood flow studies

In 21 patients who suffered aphasia resulting from left hemisphere ischemic infarction, the xenon 133 inhalation cerebral blood flow technique was used to measure cerebral blood flow within 3 months and 5 to 12 months after stroke. In addition to baseline measurements, cerebral blood flow measurements were also carried out while the patients were performing purposeful listening. In patients with incomplete recovery of comprehension and left posterior temporal-inferior parietal lesions, greater cerebral blood flow occurred with listening in the right inferior frontal region in the late studies than in the early studies. In patients with nearly complete recovery of comprehension and without left posterior temporal-inferior parietal lesions, early listening studies showed diffuse right hemisphere increases in cerebral blood flow. Later listening studies in this latter patient group showed greater cerebral blood flow in the left posterior temporal-inferior parietal region. The study provides evidence for participation of the right hemisphere in language comprehension in recovering aphasics, and for later return of function in left hemisphere regions that may have been functionally impaired early during recovery.     

Neuroimaging and recovery of language in aphasia

The use of functional neuroimaging techniques has advanced what is known about the neural mechanisms used to support language processing in aphasia resulting from brain damage. This paper highlights recent findings derived from neuroimaging studies focused on neuroplasticity of language networks, the role of the left and right hemispheres in this process, and studies examining how treatment affects the neurobiology of recovery. We point out variability across studies as well as factors related to this variability, and we emphasize challenges that remain for research.     

Recovery from vascular aphasia: prognostic factors and evidence from functional brain imaging

INTRODUCTION: Aphasia is a devastating language impairment resulting from acquired brain damage and resulting in severe communication handicap. Aphasia onset is generally followed by some degree of recovery. STATE OF ART: Prognosis of recovery is considered to depend upon a series of interacting neurobiological and individual factors. Prognosis is better determined based on neurobiological factors, whereas individual factors have a less predictable clinical outcome value. In addition, the results of recent functional neuro-imaging studies allow us to better understand the functional anatomy of the recovery from vascular aphasia. The neuro-imaging literature suggests that recovery from aphasia could depend upon right homologous to language areas, as well as on preserved perilesional left hemisphere regions. The role of either hemisphere seems to be modulated by time elapsed after brain damage, and language processing domain. Further, increasing evidence suggests that intensive and specific language therapy may interact with brain plasticity to promote recovery in chronic and severe aphasia. PERSPECTIVE AND CONCLUSION: A better understanding of the factors determining recovery from aphasia will contribute to optimizing intervention and, consequently improve the quality of life of people with aphasia.     

Variability in recovery from aphasia

Clinicians have long recognized the enormous variability of recovery among patients with aphasia. Accordingly, the identification of specific factors most important in determining the extent of recovery has been the subject of many investigations. Yet, the reasons for two patients of the same age, nearly identical clinical presentations, and similar MRI findings having completely dissimilar recoveries are still unknown. It remains difficult for a clinician to make a valid prognosis of language recovery in an individual patient. This article provides a review of aphasia-recovery research and a framework for approaching the variability of recovery in clinical practice.     

Ataxic cerebral palsy and brain imaging]

Five cases diagnosed as having ataxic cerebral palsy were presented with their brain imaging. Case 1, a 3-year-old-girl had been floppy since 7 months of age and began ataxic walk with spastic legs from 18 months of age. MRI revealed generalized atrophy of cerebellum (especially in anterior superior part) and slight atrophy of pons. Her mother also had ataxia with spastic legs of early onset. She and her mother were thought to have an early-onset inherited non-progressive cerebellar ataxia syndrome. Case 2, a 8-year-old-girl had ataxic walk since 17 months of age. MRI revealed cerebellar atrophy especially in anterior superior part. Case 3, a 10-year-old boy was floppy since 4 months of age and suspected as ataxic at 4 years of age. He could walk only with cruches. He had dwarfism and cataracts since 4 years of age. CT and MRI revealed generalized spino-ponto-cerebellar atrophy. Final diagnosis was Marinesco-Sj?rgren syndrome. Case 4, a 10-year-old girl had opisthotonus and floppiness since 4 months of age. She could walk only with cruches. CT and MRI revealed generalized spino-ponto-cerebellar atrophy. Case 5, a 8-year-old boy showed head nodding and nystagmus since 4 months of age. He started ataxic gait at 8 years of age. He could vocalize only single sound for speech. MRI revealed cranium bifida and agenesis of anterior medullar velum. Ataxic cerebral palsy is the term often used to describe very different conditions, the clinical picture starts as hypotonia and changes into the ataxic symptoms in a few years.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gender and recovery from aphasia after stroke

Moderate and severely impaired poststroke aphasic patients followed in a rehabilitation medicine program were systematically examined initially between 4 and 6 months poststroke and again between one and 2 1/2 years postonset. No gender differences were found on ratings of everyday communication function or certain measures of language, specifically auditory comprehension and the spontaneous generation of spoken words.     

Symptomatology of aphasia]

Recently, some standard test batteries such as Boston Diagnostic Aphasia Examination and Western Aphasia Battery are frequently used to assess language abnormalities and to identify individual types of aphasia. Aphasia is, however, a neurologic disorder and differential diagnosis of the type should be made naturally in the neurological examination. Characteristics of verbal output are most important clinically for the classification. The table shows core symptoms of classical aphasic types. The figure presents a systematic approach to aphasia diagnosis based on several different patterns of aphasic output.