Neural correlates for recognition memory --An investigation using functional magnetic resonance imaging and event related potential--

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The present study investigated neural correlates for episodic memory in normal volunteers using functional magnetic resonance imaging (fMRI) and event-related potential (ERP). fMRI can measure brain activity associated with cognitive tasks with high spatial resolution and ERP provides information of neural responses with high temporal resolution. Combining these two modalities offers a unique opportunity to investigate where and when a particular neural response occurs within the human brain.The first study examined whether blood-oxygen-level-dependent (BOLD) signal obtained by fMRI and electrical potentials measure by ERP would correlate each other. For this purpose, normal volunteers underwent both fMRI and ERP in separate sessions while they were performing a face recognition task. A voxel-by-voxel correlation analysis revealed that BOLD signal and ERP amplitude for face minus house condition significantly correlated in the right temporal areas. The results indicated a close relatio … More nship between the data obtained by using the two modalities.In the second study, a recognition memory for pictures was investigated using fMRI and ERP in different group of subjects. In an fMRI study successful recognition of studied items involved neural activation in the fronto-parietal areas, while in an ERP study, this cognitive process evoked large positive potential in parietal electrodes at around 500 ms after stimulus onset. These two responses probably reflected neural activity of the same group of neurons while the subjects correctly recognized the studied items. In addition, fMRI study revealed that the left front-parietal areas are particularly important for recollective process of episodic memory.Finally, recognition memory for pictures was studied using fMRI and normal elderly subjects. These elderly subjects were healthy and independently living in the community. With regard to the neural correlates for successful retrieval, the elderly group showed less activation in the left hippocampus and more activation in the retrosplenial cortex than the young group. Less