Can medial temporal lobe regions distinguish true from false? An event-related functional MRI study of veridical and illusory recognition memory

To investigate the types of memory traces recovered by the medial temporal lobe (MTL), neural activity during veridical and illusory recognition was m easured with the use of functional MRI (fMRI). Twelve healthy young adults watched a videotape segment in which two speakers alternatively presented l ists of associated words, and then the subjects performed a recognition tes t including words presented in the study lists (True items), new words clos ely related to studied words (False items), and new unrelated words (New it ems). The main finding was a dissociation between two MTL regions: whereas the hippocampus was similarly activated for True and False items, suggestin g the recovery of semantic information, the parahippocampal gyrus was more activated for True than for False items, suggesting the recovery of percept ual information. The study also yielded a dissociation between two prefront al cortex (PFC) regions: whereas bilateral dorsolateral PFC was more activa ted for True and False items than for New items, possibly reflecting monito ring of retrieved information, left ventrolateral PFC was more activated fo r New than for True and False items, possibly reflecting semantic processin g. Precuneus and lateral parietal regions were more activated for True and False than for New items. Orbitofrontal cortex and cerebellar regions were more activated for False than for True items. In conclusion, the results su ggest that activity in anterior MTL regions does not distinguish True from False, whereas activity in posterior MTL regions does.