Abstracts

Identification of eloquent cortex is a crucial issue in the preoperative assessment of patients with medically intractable epilepsy to reduce the risk of postoperative cognitive decline. Functional transcranial Doppler sonography (fTCD) is already a well established tool for language lateralisation. In this study we evaluated a fTCD-paradigm that reliably lateralises to the non-dominant hemisphere. 30 right handed healthy controls (17 male; 13 female age=27,1 [plusmn] 7,5) participated in the study. While measuring cerebral blood flow velocity (CBFV) simultaneously and continuously in both middle cerebral arteries (MCA), all patients performed a mental rotation paradigm (cube filled with three ropes had to be rotated mentally to imagine views from different sides). The paradigm consisted of 20 activation and resting periods. In addition, the already established lexical fluency paradigm for language lateralisation was performed. Data were analysed offline with the software Average[reg], which performs a heart-cycle integration and a baseline-correction and calculated a laterality index (LI) with its standard error of the mean increase in blood flow separately for both MCA during activation. One out of the 30 participants showed atypical right hemispheric language dominance and was excluded from further analysis. 21 participants (72%) of the 29 with left hemispheric language dominance showed right hemispheric dominance in the mental rotation paradigm. 7 (24%) patients generated greater left than right hemispheric activation and one participant did not show any lateralisation. There was no significant correlation between the LI in the mental rotation paradigm and test performance and no significant negative correlation between the LI of the mental rotation and the language paradigm. In more than two thirds of the participants the mental rotation paradigm showed a right hemispheric lateralisation. So far, mental rotation appears to be one of the best paradigm to activate predominantly the non-dominant hemisphere in fTCD. Participants will be interviewed to elucidate whether different especially verbal strategies could be responsible for left hemispheric lateralisation in some participants. Evaluation of this paradigm in epileptic patients is warranted.