Limitations to plasticity of language network reorganization in localization related epilepsy

Abstract

Neural networks for processing language often are reorganized in patients with epilepsy. However, the extent and location of within and between hemisphere re-organization are not established. We studied 45 patients, all with a left hemisphere seizure focus (mean age 22.8, seizure onset 13.3), and 19 normal controls (mean age 24.8) with an fMRI word definition language paradigm to assess the location of language processing regions. Individual patient SPM maps were compared to the normal group in a voxel-wise comparison; a voxel was considered to be significant if its z-value exceeded mid R:2mid R:. Subsequently, we used principal component analysis with hierarchical clustering of variance patterns from individual difference maps to identify four patient sub-groups. One did not differ from normal controls; one had increased left temporal activation on the margin of regions activated in controls; two others had recruitment in right inferior frontal gyrus, middle frontal gyrus and temporal cortex. Right hemisphere activation in these two groups occurred in homologues of left hemisphere regions that sustained task activation. Our study used novel data driven methods to find evidence for constraints on inter-hemispheric reorganization of language in recruitment of right homologues, and, in a subpopulation of patients, evidence for intra-hemispheric reorganization of language limited to the margins of typical left temporal regional activation. These methods may be applied to investigate both normal and pathological variance in other developmental disorders and cognitive domains.

Functional MRI, resting state fMRI, and DTI for predicting verbal fluency outcome following resective surgery for temporal lobe epilepsy

“…Prior research has demonstrated that TLE with an early age of onset 15,16,30 or long duration 4 can reorganize the neural representation of language. Ours is the first report that ATL, in the setting of a good seizure outcome, also results in a change in the neural representation of language evident both in terms of regional activation and the functional and white matter connectivity between these regions.…”

What do patients with epilepsy tell us about language dynamics? A review of fMRI studies

“…Data from epilepsy patients undergoing invasive electrical stimulation mapping (Ojemann et al, 1989) and noninvasive fMRI (Mbwana et al, 2009;Perrone-Bertolotti et al, 2012a) have provided little evidence of this pattern of functional reorganization. Rosenberger et al (2009) showed that patients with LH EZ could recruit LH areas outside the classical 'eloquent regions' to ensure efficient language processing (Mbwana et al, 2009;Perrone-Bertolotti et al, 2012a). Nevertheless, the intrahemispheric pattern of reorganization is more difficult to explore with classical fMRI analysis methods.…”

Insights into Adult Postlesional Language Cortical Plasticity Provided by Cerebral Blood Oxygen Level–Dependent Functional MR Imaging

“…While activation in right hemispheric cortical regions may indicate newly reorganized language-processing function, which previously was represented in the left hemisphere, it may also simply represent activation reflecting recruitment of these areas by some patients to achieve adequate task performance by compensating for inadequacy of the typical left hemispheric areas for this purpose. 10 It has been well-documented that increased language task difficulty or linguistic complexity is generally associated with increased magnitude and spatial extent of right hemispheric language cortical activation. [10][11][12] Rosenberger et al, 13 in their study of 50 patients with a left hemispheric seizure focus and 20 right-handed controls, found increased frequency of activation in right hemispheric homologues of Broca area and broadly defined Wernicke area in the patient group, but they did not find evidence for intrahemispheric reorganization in patients who were left-language-dominant.…”

“…Brain injury or epilepsy onset before 6 years of age is associated with interhemispheric transfer of language representation as demonstrated by Wada testing or fMRI and is also supported by behavioral studies of children with early brain injury. 10,[14][15][16][17] There is ample evidence that early-onset left hemispheric brain lesions do not result in long-term language disabilities that are common in adult patients who experience left-hemispheric stroke. 18 Transcallosal reorganization is often seen in such cases with involvement of right hemispheric cortical regions that are homotopic to the left hemispheric regions involved in language processing under normal conditions, with resultant normal language function, though subtle deficits in certain nonlanguage functions (eg, visuospatial processing) generally represented in the right hemisphere have been noted in some individuals on neuropsychological testing.…”