2. Diagnostic Radiology, Department of Clinical Sciences, Lund, Skåne University Hospital, SE-221 85 Lund, Sweden.
Title: Verbal encoding fMRI paradigm adds complementary information to cerebral language lateralization.
Purpose: To explore two conceptually different fMRI paradigms’ ability to lateralize language.
Methods: A verbal encoding paradigm and a word generation task were performed by six patients (four right-handed) with therapy-resistant temporal lobe epilepsy (TLE), and by ten healthy individuals (five right-handed). FMRI laterality indices (LI) and laterality curves for the anterior cerebral language regions were calculated. Typical lateralization was defined as left-hemisphere dominance, and a typical as bilateral or right-hemisphere dominance.
Results: Both paradigms showed predominantly left-sided activation in the anterior language regions, with typical contralateral cerebellar activity. Thirteen out of sixteen subjects showed concordant language lateralization results for both paradigms. Two subjects, both left-handed, showed discordant language lateralization results. Laterality curves added information for individual subjects with uncharacteristic results. The verbal encoding task showed overall more widespread activation compared to the word generation task.
Conclusion: Our results indicate valid language lateralization obtained by the fMRI verbal encoding paradigm for right-handed subjects. This offers the opportunity to simultaneously study two cognitive functions, language and verbal encoding, using one task. TLE is a network disease which predisposes afflicted patients to cortical reorganization and inserting uncertainties regarding hemisphere dominance. Atypical language representation in connection with left-handedness should be interpreted with caution irrespective of which paradigm is chosen.
Keywords: TLE, fMRI, handedness, lateralization index, language lateralization