Visual imagery deficits, impaired strategic retrieval, or memory loss: disentangling the nature of an amnesic person's autobiographical memory deficit

Abstract

Conclusions about the duration of hippocampal contributions to our autobiographical record of personal episodes have come under intense scrutiny in recent years. Interpretation is complicated by such factors as extent and site of lesions as well as test sensitivity. We describe the case of an amnesic person, K.C., with large, bilateral hippocampal lesions who figured prominently in the development of theories of remote memory due to his severely impoverished autobiographical memory extending across his entire lifetime. However, the presence of lesions in higher-order visual cortex raises the possibility that K.C.'s retrograde autobiographical amnesia is mediated by loss of long-term visual images, whereas widespread frontal lesions suggest that his impairment may relate to deficits in strategic retrieval rather than storage. Normal performance on an extensive battery of visual imagery tests refutes the imagery loss interpretation. To test for deficits in strategic retrieval, we used a more formal autobiographical memory test requiring generation of personal events under varying levels of retrieval support. However, even with rigorous contextual prompting, K.C. produced few pre-injury recollections; all were schematic, lacking the richness of detail produced by control participants, raising doubt that his deficit is one of retrieval. Findings are discussed in the context of theories concerning the duration of hippocampal-neocortical interactions in supporting autobiographical re-experiencing. The approach we used to investigate the effects of different lesions on memory provides a framework for dealing with other patients who present with an interesting functional deficit whose neuroanatomical source is difficult to specify due to widespread lesions.