Neural activity related to self-initiating elaborative semantic encoding in associative memory.

During episodic memory encoding, elaborative encoding strategies have been related to greater performance on later memory tests. However, many clinical populations display a deficit in self-initiating encoding strategies. We designed an fMRI study to examine the neural correlates of self-initiating elaborative encoding. Twenty-three healthy participants were presented triads of objects in which either neither, one or both objects in the bottom of the triad were related to the top object, and given two encoding instructions that required them to indicate the number of semantic ("related?") or physical ("smaller?") relationships in the triad. Reaction time decreased with more semantic relationships for both encoding instructions, indicating that semantic analysis was performed during the non-semantic encoding task. Recognition memory was better for the semantic encoding condition ("related?"), but there was no modulation of the number of semantic links on memory performance for either encoding condition. We performed a conjunction analysis on the fMRI data to find areas with greater activity for the non-semantic>semantic encoding tasks that were modulated by increasing semantic relationships during non-semantic encoding. Activity was found in the left dorsolateral prefrontal cortex (DLPFC) and bilaterally in the supramarginal gyrus. We suggest that the DLPFC is the most likely candidate region for the self-initiation of elaborative encoding while the supramarginal activity is likely related to attentional effects.