How Close is fMRI to Providing the Memory Component of the Wada Test?
Authors: Abou-Khalil Bassel W. 
Published: September 2005

Functional MRI Predicts Postsurgical Memory following Temporal Lobectomy

Rabin ML, Narayan VM, Kimberg DY, Casasanto DJ, Glosser G, Tracy JI, French JA, Sperling MR, Detre JA

Brain 2004;127:2286–2298

Temporal lobectomy is an effective therapy for medically refractory temporal lobe epilepsy (TLE), but may be complicated by amnestic syndromes. Therefore, presurgical evaluation to assess the risk/benefit ratio for surgery is required. Intracarotid amobarbital testing (IAT) is currently the most widely used method for assessing presurgical memory lateralization but is relatively invasive. Over the past decade, functional MRI (fMRI) has been shown to correlate with IAT for language lateralization and for memory lateralization in a small number of patients. This study was carried out to compare fMRI during memory encoding with IAT testing for memory lateralization and to assess the predictive value of fMRI during memory encoding for postsurgical memory outcome. Thirty-five patients with refractory TLE undergoing presurgical evaluation for temporal lobectomy and 30 normal subjects performed a complex visual scene-encoding task during fMRI scanning at 1.5 T by using a 10-min protocol. Encoding performance was evaluated with subsequent recognition testing. Twenty-three patients also completed the same task again outside the scanner, an average of 6.9 months after surgery. A region of interest (ROI) analysis was used to quantify activation within hippocampal and a larger mesial temporal lobe ROI consisting of hippocampus, parahippocampus, and fusiform gyrus (HPF), as defined by a published template. Normal subjects showed almost symmetrical activation within these ROIs. TLE patients showed greater asymmetry. Asymmetry ratios (ARs) from the HPF ROI correlated significantly with memory lateralization by IAT. HPF ARs also correlated significantly with memory outcome, as determined by a change in scene recognition between presurgical and postsurgical trials. When absolute activation within the HPF ROI was considered, a significant inverse correlation between activation ipsilateral to temporal lobectomy and memory outcome was observed, with no significant correlation in the contralateral HPF ROI. Although further technical improvements and prospective clinical validation are required, these results suggest that mesial temporal memory activation detected by fMRI during complex visual scene encoding correlates with postsurgical memory outcome and supports the notion that this approach will ultimately contribute to patient management.

Pre-operative Verbal Memory fMRI Predicts Post-operative Memory Decline after Left Temporal Lobe Resection

Richardson MP, Strange BA, Thompson PJ, Baxendale SA, Duncan JS, Dolan RJ

Brain 2004;127:2419–2426

Functional MRI (fMRI) of cognitive tasks depends on technology widely available in the clinical sphere but has yet to show a role in the investigation of patients. We report here the first demonstration of a clinically valuable role for cognitive fMRI. Temporal lobe epilepsy (TLE) is commonly caused by hippocampal sclerosis and is frequently resistant to drug treatment. Surgical resection of the left hippocampus in this setting can cure seizures but may produce significant verbal memory decline, which is hard to predict. We report 10 right-handed TLE patients with left hippocampal sclerosis who underwent left hippocampal resection. We compared currently used data for the prediction of postoperative verbal memory decline in such patients with a novel fMRI assessment of verbal memory encoding. Multiple regression analyses showed that fMRI provided the strongest independent predictor of memory outcome after surgery. At the individual subject level, the fMRI data had high positive predictive value for memory decline.