Interhemispheric and intrahemispheric language reorganization in complex partial epilepsy

Abstract

Objective: To investigate interhemispheric and intrahemispheric reorganization in patients with localization-related epilepsy. Method:We studied 50 patients with a left hemispheric focus and 20 normal right-handed controls with a 3T echoplanar imaging blood oxygen level dependent functional MRI auditory-based word definition decision task. Data were analyzed using SPM 2. Using region of interest for Broca and Wernicke areas and an asymmetry index (AI), patients were categorized as left language (LL; AI Ն0.20) or atypical language (AL; AI Ͻ0.20) for region. The point maxima activation for normal controls (p Ͻ0.05 corrected FDR) was identified in Broca and midtemporal regions and then used as a point of reference for individual point maxima identified at p Ͻ 0.001, uncorrected. Results:Patient groups showed increased frequency of having activation in right homologues.Activation in AL groups occurred in homologous right regions; distances for point maxima activation in homologous regions were the same as point maxima distances in normal control activation in left regions. Distances for LL patient in left regions showed a trend for differences for midtemporal gyrus (6 mm posterior, 3 mm superior) but variability around mean difference distance was significant. There was no effect of age at epilepsy onset, duration, or pathology on activation maxima. The ability to process language typically resides in the left hemisphere. Conclusions:1,2 Atypical language dominance occurs in 4%-6% of the normal right-handed population and 22%-24% of normal left-handed individuals.3,4 MRI is effective in determining language lateralization as well as identifying the location of language processing areas. 5,6 Functional MRI (fMRI) may also be used to describe the effects of epilepsy on language networks as well as assisting in presurgical planning. [7][8][9] Patients with epilepsy, regardless of handedness, have a high likelihood of atypical language.3,10,11 Early cortical injury or epileptic activity may ultimately lead to language reorganization. 11,12 The younger the brain insult, if focal, the more likely the reorganization of language functions occurs with preservation of function. 2,13 Patients with a seizure focus in the left temporal lobe are more likely to have language activation in the right hemisphere.

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

“…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.…”

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

“…The typical left-hemisphere (LH) language lateralization (see Figure 2) may be modulated in neurological condition (Rasmussen and Milner, 1977;Springer et al, 1999), and language representation may be atypical in patients with disorders such as epilepsy (Billingsley et al, 2001;Adcock et al, 2003;Sabbah et al, 2003;Berl et al, 2005Berl et al, , 2014Brázdil et al, 2005;Goldmann and Golby, 2005;Thiel et al, 2006;Lee et al, 2008;Rosenberger et al, 2009;Yu et al, 2011;Dijkstra and Ferrier, 2013).…”

“…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.…”

“…Indeed, Mbwana et al (2009) pointed out that comparisons of patients and healthy subjects are constrained by a priori assumptions and reliance on the preselection of cerebral regions (i.e., a 'regions of interest' or ROI approach). Rosenberger et al (2009) pointed out that visual, qualitative comparisons are subjective and typical group analyses are limited by a lack of data on the heterogeneity of the patient sample. For these reasons, the incidence of intrahemisphere reorganization may be underestimated or masked, which would explain the small amount of relevant evidence in the literature.…”

Clinical Standardized fMRI Reveals Altered Language Lateralization in Patients with Brain Tumor

“…[3][4][5][6][7][8] fMRI language lateralization also has the potential to allow for the study of brain plasticity in different pathologic states, such as epilepsy and stroke. [9][10][11][12][13][14][15] The mechanisms underlying neuronal plasticity induced by brain lesions are largely unknown. Changes in transcallosal and collateral inhibition of relevant brain areas for language processing have been suggested as underlying mechanisms.…”