Bilingualism and memory: early 19th century ideas about the significance of polyglot aphasia

In the second half of the 19th century, there was very little attention given to bilingual speakers within the growing clinical literature on aphasia. The first major publication on this topic (Pitres, 1895), appeared three decades after Broca's seminal work. Previously, Ribot (1881) had discussed the phenomenon of bilingual aphasia in the context of diseases of memory. Although interest in the neurological basis of the language faculty was in fact present throughout the century, the theoretical implications of the knowledge of more than one language did not appear to be linked to this issue. A number of British authors writing in the first half of the 19th century have been identified who did consider the significance of these cases. Importantly, these writers speculated on the implication of bilingual aphasia specifically with regard to ideas about memory rather than language. Consideration of these writings helps to illuminate the history of ideas about the organization of language in the brain.     

A Review of Conduction Aphasia

In this paper, a historical overview of the interpretation of conduction aphasia is initially presented. It is emphasized that the name conduction aphasia was proposed by Wernicke and was interpreted as a disconnection between the temporal and frontal brain language areas; this interpretation was re-taken by Geschwind, attributing the arcuate fasciculus the main role in speech repetition disturbances and resulting in the so-called Wernicke-Geschwind model of language. With the introduction of contemporary neuroimaging techniques, this interpretation of conduction aphasia as a disconnection syndrome due to an impairment of the arcuate fasciculus has been challenged. It has been disclosed that the arcuate fasciculus does not really connect Wernicke’s and Broca’s areas, but Wernicke’s and motor/premotor frontal areas. Furthermore, conduction aphasia can be found in cases of cortical damage without subcortical extension. It is concluded that conduction aphasia remains a controversial topic not only from the theoretic point of view, but also from the understanding of its neurologic foundations.     

MR diffusion tensor imaging documented arcuate fasciculus lesion in a patient with normal repetition performance

Background: The pathophysiology of the syndrome of conduction aphasia has been thought to involve a disconnection between posterior and anterior language areas. The arcuate fasciculus has been one of the principal candidates for an anatomical link between Wernicke's and Broca's area, but direct evidence for its involvement in conduction aphasia has been difficult to obtain. Aims: The purpose of this study was to examine white matter tract integrity, using the novel magnetic resonance imaging technique of diffusion tensor imaging, in a patient with transcortical aphasia. Methods & Procedures: A case study of a 55-year-old, right-handed man with aphasia following a left hemisphere stroke is reported. The patient's language performance was assessed with the Boston Diagnostic Aphasia Examination twice: at 10 days and at 2 years after his stroke. An MR diffusion tensor imaging study was obtained approximately 2 years after his stroke using the 1.5 T Phillips Gyroscan NT system. White matter fibre tracts maps were reconstructed using the “FACT” algorithm. Outcomes and Results: Ten days after his stroke, the patient had a non-fluent aphasia with marked impairment of both auditory comprehension and spontaneous speech. However, repetition was relatively intact. By 2 years, when the MR diffusion tensor imaging study was performed, repetition was completely normal and the patient had only subtle deficits in areas of naming and auditory comprehension. The MR diffusion tensor imaging study revealed a lesion of the dominant hemisphere arcuate fasciculus. Conclusions: This study documents normal repetition performance in a patient who on subsequent MR diffusion tensor imaging was found to have a lesion involving the dominant hemisphere arcuate fasciculus lesion. This case adds to previously published cases of normal repetition performance despite a documented lesion of the arcuate fasciculus, and thus further challenges the traditional model of conduction aphasia invoking a critical role of this white matter tract. Our case also suggests that MR diffusion tensor imaging may be a potentially useful technique to evaluate regional involvement of specific white matter tract projections in patients with aphasia.     

An adaptive semantic matching paradigm for reliable and valid language mapping in individuals with aphasia

Research on neuroplasticity in recovery from aphasia depends on the ability to identify language areas of the brain in individuals with aphasia. However, tasks commonly used to engage language processing in people with aphasia, such as narrative comprehension and picture naming, are limited in terms of reliability (test–retest reproducibility) and validity (identification of language regions, and not other regions). On the other hand, paradigms such as semantic decision that are effective in identifying language regions in people without aphasia can be prohibitively challenging for people with aphasia. This paper describes a new semantic matching paradigm that uses an adaptive staircase procedure to present individuals with stimuli that are challenging yet within their competence, so that language processing can be fully engaged in people with and without language impairments. The feasibility, reliability and validity of the adaptive semantic matching paradigm were investigated in sixteen individuals with chronic post‐stroke aphasia and fourteen neurologically normal participants, in comparison to narrative comprehension and picture naming paradigms. All participants succeeded in learning and performing the semantic paradigm. Test‐retest reproducibility of the semantic paradigm in people with aphasia was good (Dice coefficient = 0.66), and was superior to the other two paradigms. The semantic paradigm revealed known features of typical language organization (lateralization; frontal and temporal regions) more consistently in neurologically normal individuals than the other two paradigms, constituting evidence for validity. In sum, the adaptive semantic matching paradigm is a feasible, reliable and valid method for mapping language regions in people with aphasia.     

Atypical conduction aphasia. A disconnection syndrome

Conduction aphasia was originally proposed to result from separation of the posterior language comprehension area and the anterior motor speech area of the left hemisphere. The arcuate fasciculus has been the most frequently suggested site of such a disconnection, but the syndrome has been reported in cases in which the abnormality involved the dominant Wernicke's area. This challenges the arcuate fasciculus theory, and it has been suggested that a cortical lesion, not a disconnection, is the crucial factor. Three new cases in which the lesion does not lie in the arcuate fasciculus are reported, two in left-handed patients with left temporoparietal lesions and one in a right-handed patient with a right temporoparietal infarct, a "crossed" aphasia. While atypical, these cases offer evidence that disconnection of the circuit linking language comprehension to motor speech output, not damage to a specific cortical region, underlies the syndrome of conduction aphasia.     

Cortical and fibre tract interrelations in conduction aphasia

Background: The syndrome of conduction aphasia is an umbrella term to label clinically heterogeneous language disorders that all include a deficit of repetition due to impaired immediate memory or, in some patients, impaired speech production. The present article reviews the currently available literature on conduction aphasia. It covers aspects of the history of conduction aphasia as a fascicular disconnection syndrome and the objections to this view and discusses the proposed subtypes of this syndrome and the underlying cortical and white matter lesions.

Aims: The primary objectives of this article are to critically review the influence of historical concepts on recent approaches to optimise existing theoretical synergies. In addition, the article seeks to advance our understanding of the first steps of verbal auditory processing in individuals with normal and impaired language skills.

Main Contribution: We present first indications for an involvement of the left hemisphere in both short- and long-term integration of auditory information derived by examining patients with (conduction) aphasia.

Conclusions: Conduction aphasia may result from left hemisphere cortical lesions or from a disconnection of critical bundles of axons (fibre tract). The exact course of the fibre tract connections and the cortical regions involved in conduction aphasia remains controversial.     

A pilot study of use-dependent learning in the context of Constraint Induced Language Therapy.

This investigation reports the results of a pilot study concerning the application of principles of use-dependent learning developed in the motor rehabilitation literature as Constraint Induced Therapy to language rehabilitation in a group of individuals with chronic aphasia. We compared treatment that required forced use of the language modality, Constraint Induced Language Therapy, (CILT) to treatment allowing all modes of communication. Both treatments were administrated intensively in a massed practice paradigm, using the same therapeutic stimuli and tasks. Results suggest that whereas both interventions yielded positive outcomes, CILT participants showed more consistent improvement on standard aphasia measures and clinician judgments of narrative discourse. These findings suggest that CILT intervention may be a viable approach to aphasia rehabilitation.     

Diffusion tensor imaging depicting damage to the arcuate fasciculus in patients with conduction aphasia: a study of the Wernicke–Geschwind model

Abstract

Objectives: In contrast with disorders of comprehension and spontaneous expression, conduction aphasia is characterized by poor repetition, which is a hallmark of the syndrome. There are many theories on the repetition impairment of conduction aphasia. The disconnection theory suggests that a damaged in the arcuate fasciculus, which connects Broca's and Wernicke's area, is the cause of conduction aphasia. In this study, we examined the disconnection theory.

Methods: We enrolled ten individuals with conduction aphasia and ten volunteers, and analysed their arcuate fasciculus using diffusion tensor imaging (DTI) and obtained fractional anisotropy (FA) values. Then, the results of the left hemisphere were compared with those of the right hemisphere, and the results of the conduction aphasia cases were compared with those of the volunteers.

Results: There were significant differences in the FA values between the left and right hemispheres of volunteers and conduction cases. In volunteers, there was an increase in fiber in the left hemisphere compared with the right hemisphere, whereas there was an increase in fiber in the right hemisphere compared with the left hemisphere in conduction aphasia patients. The results of diffusion tensor tractography suggested that the configuration of the arcuate fasciculus was different between conduction aphasia patients and volunteers, suggesting that there was damage to the arcuate fasciculus of conduction aphasia cases.

Conclusions: The damage seen in the arcuate fasciculus of conduction aphasia cases in this study supports the Wernicke–Geschwind disconnection theory. A disconnection between Broca's area and Wernicke's area is likely to be one mechanism of conduction aphasia repetition impairment.