Autobiographical significance in past and future public semantic memory: a case-study.

Refined investigation of infrequent dissociations within remote memory, such as preservation of autobiographical episodic memory and selective impairment of public semantic memory could provide some insight on the interactions of long-term memory systems and their underlying brain correlates. Combining clinical neuropsychological and neuroimaging methods in the present study, we examined a patient surgically treated for temporal lobe epilepsy showing this rare pattern of dissociation. Specifically, we investigated along the two temporal directions, past and future, his autobiographical episodic memory, semantic memory for public events and famous people and their interaction through the concept of autobiographical significance (AS). The results showed impaired ability not only to recall past but also to imagine future public events in a context of preserved past and future personal episodic memory. Remarkably, impersonal future thinking was impaired regardless of AS, while the autobiographical-significant public past knowledge relied exclusively on the patient's spared autobiographical episodic memory. These results were corroborated by neuroimaging data showing the absence of brain activation for public knowledge devoid of personal significance and activation of the autobiographical memory cerebral network for personally significant public knowledge. Our findings suggest that AS did not 'restore' the code to access public semantic memory, but bypassed it by using personal memory sources successful only for past public recollections. Therefore, remembering impersonal and imagining public events seems to require the contribution of public semantic knowledge per se. The patient's cognitive profile suggested a reorganization of memory systems.