Abstracts

Temporal lobectomy (TLY) is an effective treatment for patients with refractory temporal lobe epilepsy (TLE). The hippocampus and adjacent mesial temporal lobe (MTL) structures play a critical role in episodic memory function and so a TLY can result in serious memory decline. Adequate presurgical assessment of memory function is critical and functional MRI (fMRI) may be useful as a non-invasive alternative to the WADA test in candidates for TLY., FMRI was acquired during a scene encoding memory task in 24 patients with TLE patients and 15 healthy controls. Laterality index (LI) was calculated for entorhinal cortex (EC), hippocampus (Hp), parahippocampus (APH), and all three areas combined. The paradigm consisted of a novelty seeking task wherein subjects are instructed to look at pictures and pay attention to the inside or outside property of the image. The task evaluates encoding of novel visual information. After the scan, subjects are given a memory test where they are asked to recall whether they had seen the image during the fMRI. The post-processing is done using SPM2 Analysis software. All fMRI images are realigned, normalized, and smoothed (7.5 mm, 7.5 mm, 10 mm). A student-t test with family-wise group error (FWE) was used to show activation maps with thresholds set at P[lt]0.05 and voxel cluster of [gt]25. A Laterality index (LI) is calculated as (L-R)/(L+R). LI = -1 indicates pure right hemisphere dominance, while +1 indicates pure left hemispheric dominance. LI [ge]0.80 implies hemispheric dominance and -0.2 [lt] LI [lt] 0.2 indicates symmetric or bilateral activation., Twenty-four patients were analyzed consisting of 13 females and 11 males. There were 11 right handed, 12 left handed and 1 ambidextrous. Seizures originated from the left in 15 patients, from the right in 4 and bilateral in 5. The mean age of the patients was 42 [plusmn]13 years. Five patients activated only 1 area while eight patients activated all areas. The parahippocampus was the most often activated area and the entorhinal the least. Hemispheric dominance was observed in the EC (64%) [gt] APH (57%) [gt] Hp(50%). Left sided TLE usually activated the contralateral side, right sided and bilateral TLE usually remained on the right. Overall 62% of the patients activated at least one of their right MTL structures. The controls combined, displayed strong lateralization to the right Hp., The side of TLE does not appear to have an effect on side of activation during this encoding task. Similar to our controls, the right side was most often activated. Novelty encoding may not yield similar results as the memory tasks.[table1],