Semantic encoding and retrieval in the left inferior prefrontal cortex: A functional MRI study of task difficulty and process specificity

J. B. Demb, J. E. Desmond, A. D. Wagner, C. J. Vaidya, G. H. Glover, J. D.E. Gabrieli

Research output: Contribution to journalArticle

Abstract

Prefrontal cortical function was examined during semantic encoding and repetition priming using functional magnetic resonance imaging (fMRI), a noninvasive technique for localizing regional changes in blood oxygenation, a correlate of neural activity. Words studied in a semantic (deep) encoding condition were better remembered than words studied in both easier and more difficult nonsemantic (shallow) encoding conditions, with difficulty indexed by response time. The left inferior prefrontal cortex (LIPC) (Brodmann's areas 45, 46, 47) showed increased activation during semantic encoding relative to nonsemantic encoding regardless of the relative difficulty of the nonsemantic encoding task. Therefore, LIPC activation appears to be related to semantic encoding and not task difficulty. Semantic encoding decisions are performed faster the second time words are presented. This represents semantic repetition priming, a facilitation in semantic processing for previously encoded words that is not dependent on intentional recollection. The same LIPC area activated during semantic encoding showed decreased activation during repeated semantic encoding relative to initial semantic encoding of the same words. This decrease in activation during repeated encoding was process specific; it occurred when words were semantically reprocessed but not when words were nonsemantically reprocessed. The results were apparent in both individual and averaged functional maps. These findings suggest that the LIPC is part of a semantic executive system that contributes to the on-line retrieval of semantic information.

Original languageEnglish (US)
Pages (from-to)5870-5878
Number of pages9
JournalJournal of Neuroscience
Volume15
Issue number9
StatePublished - Jan 1 1995
Externally publishedYes

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Keywords

  • area 8
  • executive functioning
  • functional magnetic resonance imaging (fMRI)
  • implicit memory
  • prefrontal cortex
  • semantic memory

ASJC Scopus subject areas

  • Neuroscience(all)

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