Memory fMRI in left hippocampal sclerosis: optimizing the approach to predicting postsurgical memory.
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.
Department of Clinical and Experimental Epilepsy, Institute of Neurology, University College London, UK. m.richardson@ion.ucl.ac.uk
Mark P
MP
Richardson
Bryan A
BA
Strange
John S
JS
Duncan
Raymond J
RJ
Dolan
D004833:Epilepsy, Temporal Lobe / Q000473:pathology / Q000523:psychology* / Q000601:surgery*; D005071:Evoked Potentials / Q000502:physiology; D006624:Hippocampus / Q000473:pathology* / Q000503:physiopathology; D006801:Humans; D007858:Learning; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008568:Memory / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D012016:Reference Values; D013702:Temporal Lobe / Q000473:pathology / Q000503:physiopathology