The dynamics of word retrieval in major depression

Objective: Impairment in the retrieval of specific episodes from autobiographical memory is commonly observed in major depression. However, it is unclear whether impairment in retrieval processes is a general characteristic of major depression or is confined to the recollection of personal memories.This study examined the time course of the retrieval of words from semantic memory. Method: A letter fluency test was administered to 65 inpatients with major depression and 50 healthy controls. A two-parameter model was fit to the decay curve representing the production of words over a 90-second period. One parameter, N, is an estimate of the total number of words that would be generated if the respondent was given unlimited time. The other, tau, is the average of the difference in time between the first word generated and each subsequent word. Results: There was evidence of a deficit in the retrieval of words from long-term memory in depressed patients. The significant difference between groups suggested that even if given an extended period of time in which to respond to compensate for possible slowness, the depressed group would not retrieve as many words as the controls. The retrieval failure could not be attributed solely to cognitive slowing or the effects of antidepressant medication. Conclusions: The results extend findings of a deficit in the process of retrieving specific episodes from autobiographical memory and suggest that a generalised impairment in memory retrieval may be characteristic of major depression.