What happens to personal identity when semantic knowledge degrades? A study of the self and autobiographical memory in semantic dementia.

While the self has been extensively explored in amnesic patients with severe episodic but not semantic memory disturbance, little is known about the self in semantic dementia (SD), which generally features the reverse pattern of impairment. In the present study, we investigated the structural (self-representations) and functional (consciousness) dimensions of the self in a group of eight SD patients in the early to moderate stages of the disease. We used two original tasks designed to probe both structural characteristics, namely the strength and the certainty of self-concept and the episodic/semantic nature of self-representations, and functional characteristics, namely autonoetic/noetic level of consciousness, self-evaluation and self-projection into the past, present and future. Results for the structural self showed impairment on the semantic aspects of the self-representations, except for those related to the present. Moreover, SD patients were affected regardless of the episodic or semantic nature of self-representations into the future. As regards the functional self, self-projection and level of consciousness were only impaired for the future. This study confirms the persistence of a feeling of identity in SD over time for the past and present selves. However, it also highlights the loss of the future self in SD patients. These results are discussed in relation to models of long-term memory and future thinking focusing on the interplay of episodic and semantic memory and mental time travel.