Effects of Unilateral Hippocampal Neural Loss on Brain Activity during Episodic Retrieval: A Combined H-spectroscopy and Meg/EEG Study in Patients with Temporal Lobe Epilepsy

Abstract:
Abstract: Hippocampal neural loss was measured using H-Spectroscopy in 15 Patients with temporal lobe epilepsy (7 left- and 8 right-sided). N-Acetyl-Aspartate (NAA, a marker of intact neurons) was significantly decreased compared to Creatinin and Cholin (both markers of glial cells) in the hippocampus ipsilateral to the affected temporal lobe. In the same patients EEG/MEG indices of episodic recognition were measured. Lists of 12 words were studied and each list was followed by a test list of 24 words (12 old and 12 new). There was a significant amplitude difference between EEG/MEG waveforms of old and new words (280 to 700 milliseconds). With MEG, this old/new difference was lateralized to the unaffected hemisphere. There was a tendency towards a correlation (two-tailed Pearson correlation p=.07) between the lateralization of the old/new difference (old/new difference on the healthy minus the affected side) and the lateralization of neural loss [NAA/(Creatinin + Cholin) on the healthy minus the affected side]. These data suggest that unilateral hippocampal neural loss affects the functional organization of episodic retrieval in that resources from the hemisphere with the healthy hippocampus are preferentially allocated.