Prefrontal activation for integration of object and location in working memory

Objective: To explore the neural basis of the information integration process that is critical to the episodic buffer using functional magnetic resonance imaging (fMRI). Methods: Eight normal subjects were instructed to perform a working memory task while being scanned with a 1.9 T MRI scanner. In the bound condition, subjects saw three displays in sequence, each with one object at a periphery location. While in the unbound condition, one central object and one peripheral cross were simultaneously presented, subjects were told to first picture the object in the location marked by the cross, and then to remember the object-location pairing as in the bound condition. Subjects were to determine if the probe object occupied its original location (in the bound condition) or its imaginary location (in the unbound condition). Results: Regions in bilateral middle / inferior frontal gyms, parietal cortex and cerebellum were found activated when participants constructed coherent representations of object and location that were perceptually unbound, relative to when these information were perceptually bound. Meanwhile, there were no activation for the bound condition versus unbound condition. Conclusion: Results demonstrate a clear involvement of prefrontal cortex in the creation of new cognitive representations that are not perceptually given. With existing evidence identifying prefrontal cortex in chunking and maintaining integrated representations, this study further characterizes the neural basis of information integration process in the episodic buffer.