|Title||Retrieval induced forgetting in depression and schizophrenia: role of mood and the cholinergic system|
Retrieval-induced forgetting (RIF) is a robust phenomenon, which holds that recalling information from long-term memory can suppress the accessibility of related
representations. Both inhibitory and interference processes have been identified as potential mechanisms that may underlie these automatic effects of retrieval.
Depression and schizophrenia are known to be associated with inhibitory deficits and there is evidence demonstrating a reduced RIF among these disorders. Very few
studies have however investigated RIF in these disorders and the mixed findings
reported in the literature are inconclusive.
This programme of research addressed methodological issues surrounding the RIF
procedure along with mediating factors contributing to the inhibitory processes that underlie this mechanism. These factors have been largely ignored thus far, however there is evidence that mediation of the cholinergic system with nicotine increases RIF whilst low mood reduces the RIF effect. In a series of studies, selected
neuropsychological measures, RIF, smoking status and mood were assessed in a
sample of individuals with clinical depression, individuals with schizophrenia, healthy control comparisons, a group of twin pairs diagnosed with schizophrenia and a group of healthy twin pairs.
Within depression and schizophrenia both groups demonstrated the standard pattern of RIF. However this effect was significantly reduced in the clinical groups in
comparison to the healthy controls, indicating an impaired RIF effect in individuals with depression and schizophrenia. A study investigating the different RIF
procedures revealed that RIF may be a stable measure over time. However it may
not be a heritable aspect of cognition as the study of twin pairs revealed no evidence of a genetic association. RIF was however, found to be associated with smoking
status and mood in both patients and controls with a reduction in RIF with low mood and an increase in RIF with smoking status.
These findings confirm that RIF is an important factor in depression and
schizophrenia with potential implications for clinical settings. The twin study suggests that RIF is most likely influenced by environmental factors. Indeed modulation of the cholinergic system and mood were found to play a part in mediating inhibitory
processes that underlie RIF. These findings have important implications for the
theoretical accounts of RIF and the neurochemical bases of inhibitory processes.