Rationale:
The posteromedial cortex (PMC), comprising the precuneus, the posterior cingulate, and the retrosplenial regions, is known to be engaged in various self-referential functions. However, most of the evidence so far comes from correlative evidence using neuroimaging methods. The current work was designed to test the causal relevance of specific PMC subregions for self-referential processing.
Methods:
In nine epilepsy patients with bilaterally implanted PMC electrodes, we applied direct cortical electrical stimulation within discrete PMC sites while probing changes in the participants’ subjective states. To examine the functional and causal connectivity profiles of the PMC sites that can robustly induce a change of subjective states, we applied seed-based functional connectivity with resting-state fMRI and cortico-cortical evoked potential analyses. Additionally, we administered an autobiographical episodic memory task examining the responsiveness of discrete PMC neuronal populations during retrieval of self-related autobiographical memories.
Results:
We found that in all nine participants, the electrical perturbation of only the anterior precuneus (aPCu), but not the other PMC sites, caused apparent dissociative changes in the physical and spatial bodily domain involving head, trunk, and legs. The responsive aPCu sites did not exhibit event-related activation during a cued autobiographical memory recall task. Furthermore, resting-state functional connectivity with functional Magnetic Resonance Imaging data and effective connectivity with single-pulse electrical stimulation procedures confirmed that the responsive aPCu sites were distinct from, while closely connected with, the adjacent PMC nodes of the default mode network (DMN).
Conclusions:
Based on this data, we conclude that the aPCu is a distinct functional unit within the PMC and causally important for processing self-referential information in the physical and spatial domains. Future larger scale experimental studies are needed to explore how operations of distinct neuronal populations within the PMC are integral to various cognitive processes that require a reference to self in its various dimension.
Funding:
This research was supported by a generous fund from T Zhang family.