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Memory fMRI in left hippocampal sclerosis

Optimizing the approach to predicting postsurgical memory

From the Wellcome Department of Imaging Neuroscience (B.A.S., R.J.D.) and Department of Clinical and Experimental Epilepsy (M.P.R., J.S.D.), Institute of Neurology, University College London, and National Society for Epilepsy Chalfont Centre (J.S.D.), Chalfont St. Peter, UK.

Address correspondence and reprint requests to Dr. M. Richardson, Institute of Neurology, Box 29, Queen Square, London WC1N 3BG, UK; e-mail: m.richardson{at}ion.ucl.ac.uk

Background: An optimal technique for clinical memory fMRI is not established. Previous studies suggest activity in right parahippocampal gyrus and right hippocampus shows the strongest difference between left hippocampal sclerosis (HS) patients and normal control subjects and that the difference in activity between left and right hippocampus predicts postoperative memory change.

Methods: The authors studied 30 patients with mesial temporal lobe epilepsy (mTLE) and left HS, 12 of whom subsequently underwent surgery, and 13 normal control subjects. The patients who had surgery underwent neuropsychometric evaluation pre- and postoperatively. All subjects underwent a verbal memory encoding event-related fMRI study. Activation maps were assessed visually. Subsequently, the brain regions involved in the memory task were revealed by group averaging; these regions were used to determine regions of interest (ROIs) for subsequent analysis. By use of stepwise discriminant function and stepwise multiple regression, the ROIs that optimally discriminated between patients and normal control subjects and that optimally predicted postoperative verbal memory outcome were determined.

Results: Visual inspection of individual patient activation statistic maps revealed noisy data that did not afford visual interpretation. Stepwise discriminant function revealed the difference between left and right hippocampal activity best discriminated between patients and normal control subjects. Stepwise multiple regression revealed left hippocampal activity was the strongest predictor of postoperative verbal memory outcome; greater left hippocampal activity predicted a greater postoperative decline in memory.

Conclusions: Patients with left hippocampal sclerosis (HS) differ from normal control subjects in the distribution of memory-encoding activity between left and right hippocampus. Functional adequacy of left hippocampus best predicts postoperative memory outcome in left HS.

Additional material related to this article can be found on the Neurology Web site. Go to www.neurology.org and scroll down the Table of Contents for the March 14 issue to find the title link for this article.

M.P.R. is funded by a fellowship of the Medical Research Council UK. The scanning was carried out under a Wellcome Trust Program Grant to R.J.D.

Disclosure: The authors report no conflicts of interest.

Received July 24, 2005. Accepted in final form November 9, 2005.

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