Level of sustained entorhinal activity at study correlates with subsequentcued-recall performance: A functional magnetic resonance imaging study with high acquisition rate

Functional magnetic resonance imaging (fMRI) with high acquisition rate was performed during the intentional memorizing of words to specify which medi al temporal lobe structure is important in determining what words are subse quently remembered in a cued-recall test and to characterize the time cours e of activation in that structure. Functional images of six healthy young s ubjects were analyzed by two subject- and voxel-wise statistics: First, to identify brain areas transiently engaged in encoding of words, brain activi ty during memorizing visually presented words and watching a fixation cross was compared by a Kolmogorov-Smirnov statistic (KS-test). Second, to ident ify brain areas whose activity correlates with memory encoding success, a K endall's correlation was calculated between signal intensity at study and p erformance in a subsequent cued-recall test. Averaged signal intensities we re plotted as a function of time to depict the time course of brain activit y detected by both statistical tests. The level of slowly modulated, sustai ned activity in Brodmann area 28 (entorhinal cortex) did not respond transi ently as study words appeared, but did correlate positively with subsequent test performance. More left than right activity in Brodmann area 45 (dorso -lateral prefrontal cortex) and bilateral activity in Brodmann area 44 (pre motor cortex) exhibited transient hemodynamic responses that did not show a ny relation to subsequent memory performance. Thus, the study identified a novel pattern of slowly modulated brain activity in human entorhinal cortex that may represent a declarative memory encoding state whose level predict s whether experiences will be remembered or forgotten. Hippocampus 1999;9:3 5-44. (C) 1999 Wiley-Liss, Inc.