Decrements in Hippocampal Activity with Item Repetition during Continuous Recognition: An fMRI Study

摘要

fMRI (1.5mmisotropic voxels) was employed to investigate thenrelationship between hippocampal activity and memory strengthnin a continuous recognition task. While being scanned, subjectsnwere presented with colored photographs that each appearednon four occasions. The requirements were to make onenresponsewhen an itemwas presented for the first or the third timenand to make a different response when an item appeared for thensecond or the fourth time. Consistent with prior findings, itemsnpresented for the first time elicited greater hippocampal and parahippocampalnactivity than repeated items. The activity elicitednby repeated items declined linearly as a function of number ofnpresentations (“graded” new > old effects). No medial-temporalnlobe regions could be identified where activity elicited by repeatednitems exceeded that for new items or where activity elicitednby repeated items increased with number of presentations.nThese findings are inconsistent with the proposal that retrievalrelatednhippocampal activity is positively correlated with memorynstrength. We also identified graded new > old effects in severalncortical regions outside the medial-temporal lobe, including thenleft retrosplenial/posterior cingulate cortex and the right lateralnoccipito-temporal cortex. By contrast, graded old > new effectsnwere evident in bilateral mid-intraparietal sulcus and precuneus. ■