Abnormal Cortical Network Activation in Human Amnesia: A High-resolution Evoked Potential Study
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Little is known about how human amnesia affects the activation of cortical networks during memory processing. In this study, we recorded high-density evoked potentials in 12 healthy control subjects and 11 amnesic patients with various types of brain damage affecting the medial temporal lobes, diencephalic structures, or both. Subjects performed a continuous recognition task composed of meaningful designs. Using whole-scalp spatiotemporal mapping techniques, we found that, during the first 200 ms following picture presentation, map configuration of amnesics and controls were indistinguishable. Beyond this period, processing significantly differed. Between 200 and 350 ms, amnesic patients expressed different topographical maps than controls in response to new and repeated pictures. From 350 to 550 ms, healthy subjects showed modulation of the same maps in response to new and repeated items. In amnesics, by contrast, presentation of repeated items induced different maps, indicating distinct cortical processing of new and old information. The study indicates that cortical mechanisms underlying memory formation and re-activation in amnesia fundamentally differ from normal memory processing.
KeywordsAmnesia Recognition memory Encoding Brain damage Evoked potentials Brain mapping EEG Spatiotemporal analysis
We thank Stephanie Clarke, Rolf Frischknecht, and Micah Murray for their support and Christoph Michel for helpful comments. The Cartool software was programmed by Denis Brunet; development of the software was supported by the Center for Biomedical Imaging (CIBM) of Geneva and Lausanne. The study was supported by Swiss National Science Foundation grant no. 320000-113436 to A.S.
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