Brain activation during a linguistic task in conduction aphasia

Cortical Reorganization after Rehabilitation in a Patient with Conduction Aphasia Using High-Density EEG

Conduction aphasia is a language disorder occurred after a left-brain injury. It is characterized by fluent speech production, reading, writing and normal comprehension, while speech repetition is impaired. The aim of this study is to investigate the cortical responses, induced by language activities, in a sub-acute stroke patient affected by conduction aphasia before and after an intensive speech therapy training. The patient was examined by using High-Density Electroencephalogram (HD-EEG) examination, while was performing language tasks. the patient was evaluated at baseline and after two months after rehabilitative treatment. Our results showed that an intensive rehabilitative process, in sub-acute stroke, could be useful for a good outcome of language deficits. HD-EEG results showed that left parieto-temporol-frontal areas were more activated after 2 months of rehabilitation training compared with baseline. Our results provided evidence that an intensive rehabilitation process could contribute to an inter- and intra-hemispheric reorganization.

Impaired speech repetition and left parietal lobe damage

Patients with left hemisphere damage and concomitant aphasia usually have difficulty repeating others' speech. Although impaired speech repetition, the primary symptom of conduction aphasia, has been associated with involvement of the left arcuate fasciculus, its specific lesion correlate remains elusive. This research examined speech repetition among 45 stroke patients who underwent aphasia testing and MRI examination. Based on lesion-behavior mapping, the primary structural damage most closely associated with impaired speech repetition was found in the posterior portion of the left arcuate fasciculus. However, perfusion-weighted MRI revealed that tissue dysfunction, in the form of either frank damage or hypoperfusion, to the left inferior parietal lobe, rather than the underlying white matter, was associated with impaired speech repetition. This latter result suggests that integrity of the left inferior parietal lobe is important for speech repetition and, as importantly, highlights the importance of examining cerebral perfusion for the purpose of lesion-behavior mapping in acute stroke.

Neuroimaging of language and aphasia after stroke

Over the past 25 years, neuroimaging techniques have advanced rapidly. These techniques, including computed tomography, magnetic resonance imaging, positron emission tomography and single photon emission computed tomography, have improved our understanding of the relationships of language, language disorder, and brain language organization. In this article, we review the contribution of these neuroimaging techniques to the fields of brain language function and speech-language disorders after ischemic stroke. We also discuss the future of these techniques in the research and clinical arenas of ischemic stroke and aphasia rehabilitation.

Conduction aphasia as a function of the dominant posterior perisylvian cortex

✓ Assessment of eloquent functions during brain mapping usually relies on testing reading, speech, and comprehension to uncover transient deficits during electrical stimulation. These tests stem from findings predicted by the Geschwind–Wernicke hypothesis of receptive and expressive cortices connected by white matter tracts. Later work, however, has emphasized cortical mechanisms of language function. The authors report two cases that demonstrate that conduction aphasia is cortically mediated and can be inadequately assessed if not specifically evaluated during brain mapping.

To determine the distribution of language on the dominant cortex, electrical cortical stimulation was performed in two cases by using implanted subdural electrodes during brain mapping before epilepsy surgery. A transient isolated deficit in repetition of language was reported during stimulation of the posterior portion of the dominant superior temporal gyrus in one patient and during stimulation of the supramarginal gyrus in the other patient.

These cases demonstrate a localization of language repetition to the posterior perisylvian cortex. Brain mapping of this region should include assessment of verbal repetition to avoid potential deficits resembling conduction aphasia.

Dysgraphia in two forms of conduction aphasia

Recent clinical observations, in the absence of experimental data, appear to suggest that written expression in conduction aphasics parallels their speech (Goodglass, 1992). The current study undertakes an analysis of word level writing in two conduction aphasics, and attempts to explore the posited 'parallel' relationship between speech production deficits and deficits in written expression. JL, a 66-year-old female with left posterior parietal lobe lesion and PP, a 65-year-old female with a left posterior temporo-parietal lobe lesion served as subjects of this study. Their response patterns on Boston Naming Test (BNT) and written naming task (John Hopkins Dysgraphia Battery) were utilized to verify the parallel hypothesis. Although both cases have exhibited phonological and semantic paraphasias on BNT, PP's overall performance was far superior to that of JL. JL produced numerous multiple responses to stimuli compared to PP's occasional multiple responses. PP's performance on the written naming task was far inferior to that of JL. JL's predominant error pattern in writing was the production of phonologically similar words to the target words. This paper argues that such seemingly contradictory, unpredicted patterns can be parsimoniously better explained, not by the parallel hypothesis but by current cognitive-neuropsychological models of writing.

Segmentation of subcomponents within the superior longitudinal fascicle in humans: a quantitative, in vivo, DT-MRI study

Previous research in non-human primates has shown that the superior longitudinal fascicle (SLF), a major intrahemispheric fiber tract, is actually composed of four separate components. In humans, only post-mortem investigations have been available to examine the trajectory of this tract. This study evaluates the hypothesis that the four subcomponents observed in non-human primates can also be found in the human brain using in vivo diffusion tensor magnetic resonance imaging (DT-MRI). The results of our study demonstrated that the four subdivisions could indeed be identified and segmented in humans. SLF I is located in the white matter of the superior parietal and superior frontal lobes and extends to the dorsal premotor and dorsolateral prefrontal regions. SLF II occupies the central core of the white matter above the insula. It extends from the angular gyrus to the caudal-lateral prefrontal regions. SLF III is situated in the white matter of the parietal and frontal opercula and extends from the supramarginal gyrus to the ventral premotor and prefrontal regions. The fourth subdivision of the SLF, the arcuate fascicle, stems from the caudal part of the superior temporal gyrus arches around the caudal end of the Sylvian fissure and extends to the lateral prefrontal cortex along with the SLF II fibers. Since DT-MRI allows the precise definition of only the stem portion of each fiber pathway, the origin and termination of the subdivisions of SLF are extrapolated from the available data in experimental material from non-human primates.

Aging gracefully: compensatory brain activity in high-performing older adults

Whereas some older adults show significant cognitive deficits, others perform as well as young adults. We investigated the neural basis of these different aging patterns using positron emission tomography (PET). In PET and functional MRI (fMRI) studies, prefrontal cortex (PFC) activity tends to be less asymmetric in older than in younger adults (Hemispheric Asymmetry Reduction in Old Adults or HAROLD). This change may help counteract age-related neurocognitive decline (compensation hypothesis) or it may reflect an age-related difficulty in recruiting specialized neural mechanisms (dedifferentiation hypothesis). To compare these two hypotheses, we measured PFC activity in younger adults, low-performing older adults, and high-performing older adults during recall and source memory of recently studied words. Compared to recall, source memory was associated with right PFC activations in younger adults. Low-performing older adults recruited similar right PFC regions as young adults, but high-performing older adults engaged PFC regions bilaterally. Thus, consistent with the compensation hypothesis and inconsistent with the dedifferentiation hypothesis, a hemispheric asymmetry reduction was found in high-performing but not in low-performing older adults. The results suggest that low-performing older adults recruited a similar network as young adults but used it inefficiently, whereas high-performing older adults counteracted age-related neural decline through a plastic reorganization of neurocognitive networks.

Hemispheric asymmetry reduction in older adults: the HAROLD model

A model of the effects of aging on brain activity during cognitive performance is introduced. The model is called HAROLD (hemispheric asymmetry reduction in older adults), and it states that, under similar circumstances, prefrontal activity during cognitive performances tends to be less lateralized in older adults than in younger adults. The model is supported by functional neuroimaging and other evidence in the domains of episodic memory, semantic memory, working memory, perception, and inhibitory control. Age-related hemispheric asymmetry reductions may have a compensatory function or they may reflect a dedifferentiation process. They may have a cognitive or neural origin, and they may reflect regional or network mechanisms. The HAROLD model is a cognitive neuroscience model that integrates ideas and findings from psychology and neuroscience of aging.

Supra- and infrasylvian conduction aphasia

Fifteen cases of conduction aphasia which were tested with the Aachen Aphasia Test (AAT), are presented. The CT lesion data were transformed to a standard 3D-reference brain referring to the ACPC line. According to the lesion profiles a group of 6 patients had pure suprasylvian lesions, a group of 4 patients had pure infrasylvian lesions, and a group of 5 patients had lesions in both supra- and infrasylvian regions. Suprasylvian conduction aphasics are superior to infrasylvian conduction aphasics in the token test and in repetition tasks. Infrasylvian conduction aphasics use more stereotypes in spontaneous speech than suprasylvian conduction aphasics. Conduction aphasics with both lesion sites perform less well in tests of naming, writing, and comprehension than the pure types. Thus conduction aphasia is a heterogeneous syndrome anatomically and linguistically.

Cortical language activation in stroke patients recovering from aphasia with functional MRI

BACKGROUND AND PURPOSE

Two mechanisms for recovery from aphasia, repair of damaged language networks and activation of compensatory areas, have been proposed. In this study, we investigated whether both mechanisms or one instead of the other take place in the brain of recovered aphasic patients.

METHODS

Using blood oxygenation level-dependent functional MRI (fMRI), we studied cortical language networks during lexical-semantic processing tasks in 7 right-handed aphasic patients at least 5 months after the onset of left-hemisphere stroke and had regained substantial language functions since then.

RESULTS

We found that in the recovered aphasic patient group, functional language activity significantly increased in the right hemisphere and nonsignificantly decreased in the left hemisphere compared with that in the normal group. Bilateral language networks resulted from partial restitution of damaged functions in the left hemisphere and activation of compensated (or recruited) areas in the right hemisphere. Failure to restore any language function in the left hemisphere led to predominantly right hemispheric networks in some individuals. However, better language recovery, at least for lexical-semantic processing, was observed in individuals who had bilateral rather than right hemisphere-predominant networks.

CONCLUSIONS

The results indicate that the restoration of left-hemisphere language networks is associated with better recovery and inversely related to activity in the compensated or recruited areas of the right hemisphere.

The Copenhagen Stroke Study experience

The Copenhagen Stroke (COST) Study was a prospective, consecutive, community-based study of 1,197 patients with acute stroke who underwent acute stroke care and rehabilitation in a stroke unit setting. This article reviews the results of this study with respect to (1) the effect of organized stroke care and rehabilitation, (2) neurological outcome and functional outcome of stroke in relation to initial stroke severity and functional disability, (3) recovery of upper-extremity function and walking, (4) time course of neurological and functional recovery relative to initial stroke severity, (5) mechanisms of stroke recovery, and (6) the effect on stroke recovery of various demographic, medical, and pathophysiological factors, such as stroke in progression, spontaneous reperfusion age, diabetes, blood glucose on admission, stroke type (hemorrhage/infarction), silent infarction, and leuco-araiosis.

Effect of non-steady-state perfusion on xenon-133 cerebral blood flow measurements: an analytical study

Activation studies employing the noninvasive xenon-133 technique are widely used to investigate the cerebral circulation. Typical examples are the investigation of hemispheral specialization of higher cortical function with cognitive activation or the assessment of the hemodynamic reserve in occlusive cerebrovascular disease by CO2 inhalation. Traditionally, in studies using this technique, there is the requirement of a circulatory steady state during the measurement. Due to limitations in the duration of the stimulus or habituation to the stimulus, the basic assumption is often violated. In this study we investigated with the aid of a computer model to what extent blood flow measurement results are affected by non-steady-state blood flow. The findings indicate that cortical activation need not extend throughout the whole measurement to be detectable. Maintenance of activation for at least 5 min is sufficient for a successful measurement. In addition, the results show that the activation should be fully established when the measurement starts to achieve maximal sensitivity. Delay in activating the circulation will result in attenuated responses, especially if the stimulus is delayed beyond 2 min.