External Source Monitoring and Reality Monitoring: Meta-Analysis of fMRI Studies

Being able to remember the origin of a particular memory is for times even more important than the memory itself. Yet, although memory for the information and memory for the source are intrinsically connected, the particular neural underpinnings for the source-memory monitoring remains unclear. We run an fMRI meta-analysis to help to clarify the brain structures necessary for source memory monitoring. Source monitoring (SM) relates to distinguishing the origin of the information of two external sources, whereas reality monitoring (RM) refers to distinguishing between one internal (e.g., thoughts) and one external source, or two internal sources. We used PRISMA to select the manuscripts and Ginger ALE to analyze the data of the final 51 eligible selected articles. Most of the articles referred to external SM paradigms (34), but the number of articles on RM (17) allowed us to run a separate analysis to identify brain regions active during this specific process. The SM and RM contrasts showed concordance in 10 clusters, being the largest cluster with the highest ALE value found in the left claustrum and middle Frontal Gyrus (BA 46, 9 and 10). SM contrasts show concordance in seven clusters that include the largest cluster centered in the left middle frontal (BA 9) and inferior frontal gyrus (BA 45). Five suprathreshold clusters were detected for RM contrasts. The largest one was detected in the parietal lobe, centered in the left inferior parietal lobule (BA 40) and left angular gyrus (BA 39). The results support the neural differentiation, as well as a partial overlapping, for the two different types of monitoring. Moreover, they help to understand the divergent results in fMRI studies most likely due to the stimuli characteristics.