Direct comparison of prefrontal cortex regions engaged by working and long-term memory tasks

Area of Science:

• Cognitive Neuroscience
• Neuroimaging

Background:

• Prefrontal cortex (PFC) regions, including ventrolateral (VL-PFC), dorsolateral (DL-PFC), and frontopolar (FP-PFC), are implicated in both working memory (WM) and long-term memory (LTM).
• Previous neuroimaging studies suggest overlapping roles, necessitating direct comparisons to understand domain-specific activations within the PFC.

Purpose of the Study:

• To directly compare PFC activation patterns during WM and LTM tasks using functional magnetic resonance imaging (fMRI).
• To investigate whether specific PFC regions are selectively engaged by task type (WM vs. LTM) or stimulus material type (words vs. faces).

Main Methods:

• A within-subjects fMRI design was employed.
• Participants performed an n-back task (WM), and LTM encoding and retrieval tasks.
• Stimulus materials included familiar words and unfamiliar faces to assess material-type influence.

Main Results:

• A bilateral DL-PFC region (BA 46/9) showed selective activation during the two-back WM task, supporting its role in information maintenance/manipulation.
• Left FP-PFC was selectively engaged during the two-back task, contrary to prior associations with LTM retrieval.
• Lateralized VL-PFC regions were selectively activated by stimulus material type, independent of the memory task.

Conclusions:

• The findings differentiate PFC functions, showing task-selectivity in DL-PFC and material-selectivity in VL-PFC.
• Results challenge existing theories by demonstrating FP-PFC's involvement in WM rather than LTM retrieval.
• This study underscores the importance of examining PFC activity across diverse memory domains and material types for precise functional mapping.