Types and characteristics of remote memory impairment in schizophrenia

Remote memory, as the term is used in the present study, refers to semantic information or autobiographical information for events and facts that are thought to be stored in the neocortex. In schizophrenia, findings of abnormalities in remote memory have been reported. However, it is unclear whether these are due to retrieval factors or other factors (e.g. paucity of information, disorganized lexicosemantic representations). Furthermore, it is unclear whether there is a temporal gradient in remote memory. In the first study, we utilized a cueing procedure for semantic fluency in order to determine whether retrieval factors play a marked role in impairments. In comparing patients with schizophrenia to patients with affective disorder and normal controls, we found that cueing had an equivalent effect upon all groups, suggesting that marked retrieval deficits were not the primary determinant of poor performance in fluency. Furthermore, we found that semantic fluency was disproportionately impaired vis-a-vis phonologic fluency, suggesting that abnormalities may be greater in storage areas presumed to be in temporal parietal cortex rather than in prefrontal cortex (which has been associated with retrieval deficits). In the second study, we examined the temporal gradient of autobiographical memory in patients with schizophrenia and normal controls. Whereas normal controls exhibited high and equivalent performance across childhood, early adult, and recent memories, patients with schizophrenia exhibited a u-shaped profile perhaps unique in the neuropsychiatric literature. This may reflect a combination of secondary memory impairments which effect the acquisition of new information coupled to very mildly accelerated rate of forgetting, 'recency' effects, and/or inefficient encoding. Taken together, these studies provide further support for the notion that schizophrenia has a relatively unique pattern of neuropsychological deficit based on neocortical dysfunction that includes, though is not restricted to, temporoparietal regions.