Clinical relevance of memory performance during Wada is stimulus type dependent

Abstract

Objectives: This study aimed to investigate whether different types of memory stimulus provide different information during the Wada or intracarotid amytal procedure (IAP) in patients with refractory medial temporal lobe epilepsy (MTLE). Methods: Eighty nine surgical candidates with documented MTLE and selected for left hemispheric language dominance underwent memory assessment with verbal and dually encodable stimuli during a presurgical IAP. Results: The overall IAP memory performance with the left hemisphere is significantly better than with the right hemisphere regardless of lesion side. This can be explained by the left hemispheric advantage of encoding all stimuli, whereas the right hemisphere has only limited resources to encode verbal stimuli. More importantly, it appeared that dually encodable items remain more readily recognised following injection ipsilateral to the lesion, whereas verbal items are always better recognised following right hemisphere injection regardless of lesion side. Conclusions: Verbal IAP stimuli show left hemispheric sensitivity in left language dominant MTLE patients. The dually encodable items of the IAP appear lesion sensitive. P reoperative tests capable of quantitatively predicting memory outcome for individual patients would be an important resource for physicians and surgeons treating patients with refractory medial temporal lobe epilepsy (MTLE). An even more ambitious goal would be to predict material specific memory loss following unilateral temporal lobe resection. Centres treating patients with epilepsy have used a variety of stimuli to determine memory performance during the Wada or intracarotid amytal procedure (IAP) including real objects, line drawings, unfamiliar figures, faces, words, and rhymes.1 The few studies that have evaluated the issue of stimulus type reported that different types of stimulus contribute differently to the clinical preoperative questions that the IAP memory performance can address.2-4 We aim to investigate the effect of using verbal stimuli versus dually encodable line drawings depicting simple objects or scenes on lesion lateralisation and side of injection, and to evaluate whether different types of memory stimulus provide different information during IAP in patients with refractory MTLE. METHODS PatientsFollowing institutional approval and informed consent, 89 patients with refractory medial temporal lobe epilepsy (50 right MTLE; 39 left MTLE) were included in the study. The location of the suspected seizure focus was determined according to the standard presurgical evaluation protocol on the basis of all available data (including video-EEG, neurological examination, structural MRI, neuropsychological testing, PET, and SPECT) by members of the Reference Center for Refractory Epilepsy at Ghent University Hospital. 5 MTLE patients were included only if they had undergone bilateral IAP showing left hemispheric language dominance and had a total IQ of 60 or higher. Average age was 31.9 years (standard deviation (SD) 9.9), average duration o...

Memory performance is related to language dominance as determined by the intracarotid amobarbital procedure

“…Additionally, there is evidence that lesions of the left hippocampus tend to equalize the memory performance of the left hippocampus to that of the right hippocampus during the IAP using a mixed item stimulation paradigm in patients with mesial temporal lobe epilepsy [21] and [22]. In line with our findings, these data point to the left hippocampus as the more powerful structure in the paradigm of mixed item stimulus memory processing.…”

Repeated Intracarotid Amobarbital Tests

“…These examples support the hypothesis that the IAT memory testing may not be valid in all cases. Recent studies suggest that the clinical relevance of the IAT may be closely linked to the memory test paradigm (Vingerhoets et al, 2006a; Vingerhoets et al, 2006b) and the type of memory assessed during the IAT (Simkins‐Bullock, 2000).…”