Neural mechanisms of subliminal priming for traumatic episodic memory: an ERP study

Event-related brain potentials (ERPs) were measured to study the electrophysiological mechanisms of subliminal priming of traumatic episodic memory. Twenty-four Chinese subjects who had experienced the great Sichuan earthquake in 2008 were classified either as normal control or as post-traumatic stress disorder (PTSD) subjects. Results showed that subliminally presented earthquake-related words elicited two significantly more positive ERP deflections (P2 and P300) than did earthquake-unrelated words between 250-300 ms and 340-400 ms post-stimulus periods for the PTSD group, but not for the control group. Dipole source analysis showed that the P2 was mainly generated in the posterior cingulate cortex (PCC), which appeared to be related to unconscious attentional resource allocation to the earthquake-related words. In addition, the P300 was found to be generated in the parahippocampal gyrus, which seemed to be related to the involuntary activation of traumatic episodic memory. These results indicated that catastrophic earthquake experiences made some subjects extremely sensitive and hyper-responsive to trauma-related information.