The human dorsolateral prefrontal cortex: A critical neural module in the transformation of information within working memory. Evidence fromfMRI of deductive reasoning at 4 T

The dorsolateral prefrontal cortex DLPFC has been activated in research designed to assess executive processes that have ranged in diversity from dual-task performance to semantic comprehension. Recent characterizations of DLPFC function have been that it serves as (i) a linguistic processing module, that it (ii) “monitors the contents of working memory”, and that the DLPFC is the (iii) “central executive”. Many of claims concerning DLPFC function have been limited by research that has utilized overly simplistic control conditions as comparison points. In the present research, high-resolution functional magnetic resonance imaging (fMRI) compared the DLPFC magnetic resonance (MR) intensities resulting from deductive reasoning, semantic comprehension, grammatical processing, and memory updating tasks. A demand that was unique to the deductive task was the logical transformation of information within working memory; a process that involves integration of premise information. Study 1 demonstrated that deductive reasoning recruited the DLPFC significantly more than either grammatical processing or semantic comprehension executive tasks. In Study 2, a task was developed that required the executive process of updating the contents of working memory. Study 2 demonstrated that the storage demands of the memory-updating and deduction tasks were not significantly different. In Study 3, DLPFC MR signal intensities were found to be significantly higher during deduction than during the memory-updating task. The results indicate that the DLPFC is important in the logical transforming information within working memory. One alternate hypothesis that remained tenable was that the DLPFC moderates task difficulty.