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Neurobiology of Language Recovery After Stroke: Lessons From Neuroimaging Studies

https://doi.org/10.1016/j.apmr.2011.03.036Get rights and content

Abstract

Saur D, Hartwigsen G. Neurobiology of language recovery after stroke: lessons from neuroimaging studies.

Language is organized in large-scale, predominantly left-lateralized, temporo-parieto-frontal networks in the human brain. After focal brain damage (eg, ischemic stroke), this network organization enables the brain to adaptively reorganize language functions in order to compensate lesion effects. Here, we summarize how structural and functional neuroimaging methods contribute to the current understanding of loss and recovery of language functions after stroke. This includes voxelwise lesion-behavior mapping, functional imaging for mapping reorganizational mechanisms from acute to chronic stroke, as well as imaging based outcome prediction. The review is complemented by an introductory section on language organization in the healthy brain.

Section snippets

Imaging Language Networks in the Healthy Brain

A profound understanding of language organization in the healthy human brain is mandatory for the interpretation of activation changes due to reorganizational mechanisms in patients with brain damage. While early models of language organization were solely based on behavioral deficits in patients with brain lesions (eg, Broca2 and Wernicke3, see Shalom and Poeppel 4 for a review), a new decade of studies on language organization in the human brain has started with the advent of modern

Voxel-Based Lesion Studies of Language

Since the days of Broca and Wernicke in the second half of the 19th century, research aims at defining functional-anatomic models of language organization in the human brain. While the modularity assumption (ie, discrete anatomical modules deal with different cognitive functions) of the classical lesion-deficit approach has frequently been criticized (eg,21, 22 for reviews), the recent advent of new techniques offers a complementary approach to the use of imaging studies in healthy volunteers.

Dynamics of Language Reorganization in 3 Phases

In a behavioral study, Pedersen et al37 tested 330 patients with acute aphasia at admission as well as weekly during the hospitalization period (6–12wk poststroke) and 6 months after stroke. The authors found that the highest dynamic of language recovery can be observed in the first 2 weeks after onset, while in the later course, recovery proceeded more prolonged. These different dynamics of functional improvement suggest that different mechanisms contribute to language recovery after stroke.

Imaging Treatment-Induced Plasticity

The results of the longitudinal fMRI study on language recovery from Saur et al43 implicated that aphasic patients may be able to resort to normative learning mechanisms in the chronic phase after stroke. Consequently, it can be assumed that model-based therapeutic strategies may be best applied in the chronic phase.

Overall, it has been demonstrated that the efficacy of language therapy depends on treatment intensity. Various studies showed that high-intensive short-term interventions can

Future Directions

Within the last years, the use of functional imaging techniques has substantially increased our knowledge about brain organization, loss of functions after brain damage, and reorganizational processes. It should be noted, however, that the results from functional imaging studies are correlative in nature and do not allow for any causal conclusions. Thus, the use of a multimodal approach combining different methods, such as functional and/or structural imaging with transcranial stimulation

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