Left-sided Interictal Epileptic Activity Induces Shift of Language Lateralization in Temporal Lobe Epilepsy: An fMRI Study
Article first published online: 8 MAY 2006
Volume 47, Issue 5, pages 921–927, May 2006
How to Cite
Janszky, J., Mertens, M., Janszky, I., Ebner, A. and Woermann, F. G. (2006), Left-sided Interictal Epileptic Activity Induces Shift of Language Lateralization in Temporal Lobe Epilepsy: An fMRI Study. Epilepsia, 47: 921–927. doi: 10.1111/j.1528-1167.2006.00514.x
- Issue published online: 8 MAY 2006
- Article first published online: 8 MAY 2006
- Accepted December 8, 2005.
- Language reorganization;
- Mesial temporal lobe epilepsy;
- Interictal epileptiform discharges;
- Transient cognitive impairment;
- Functional magnetic resonance imaging
Summary: Purpose: By using speech-activated functional MRI (fMRI), we investigated whether the frequency of left-sided interictal epileptic activity (IED: spikes or sharp waves on the EEG) is associated with atypical speech lateralization.
Methods: We investigated 28 patients (13 men, aged 17–59 years) with left-sided mesial temporal lobe epilepsy (MTLE) and 11 patients with right-sided MTLE as a control population. Only patients with unilateral hippocampal sclerosis with unilateral IED were included. For fMRI of individual patients, we contrasted images sampled during covert word generation with a low-level rest condition. With SPM99, an individual comparison for the contrast “word generation versus resting inactivity” was conducted. To characterize speech lateralization in individual patients, we calculated asymmetry indexes (AIs): the difference between activated left-sided and right-sided voxels was divided by all activated voxels. Analyzing long-term EEG, the first 2 min of each hour were evaluated for the frequency of IED. Univariate associations with AIs were assessed by Pearson's correlation and by t test. When testing the independent associations, multivariate linear regression was performed.
Results: The AIs in patients with left-sided MTLE were 0.40 ± 0.53 on average (range, −0.83 to +1.0), whereas in right-sided MTLE, they were 0.78 ± 0.15 (p = 0.029). For the further investigations, we included left-sided MTLE patients only. The median frequency of IED was six per hour (range, 0–240). Higher IED frequency was correlated with left-right shift of lateralization of speech fMRI activity (p = 0.002).
Conclusions: Higher left-sided spike frequency in MTLE was associated with a left–right shift of speech representation, suggesting that chronic frequent interictal activity may induce a reorganization of speech lateralization.