A double dissociation of memory impairments in major depression

Objective: While declarative memory impairments are well known in major depression, most studies show preserved procedural memory in depressed patients. We tested if sleep-dependent procedural and declarative memory consolidation are impaired in major depression. Methods: 30 medicated patients with an acute episode of major depression and 30 normal controls were assessed using a procedural (sequential finger tapping) and a declarative (paired associates) memory task before and after a night of sleep. Results: Although depressed patients and control subjects did not differ in practice-dependent learning of the procedural task in the awake state, healthy subjects showed overnight improvements in tapping performance of 11.5%, while the patients' performance decreased overnight by 10.7%. This pattern was reversed for the declarative task: While patients learned 33.5% less word pairs than controls in the awake state, overnight changes did not differ between the two groups. Conclusions: Our results suggest a double dissociation of memory consolidation processes in major depression: Sleep-dependent memory consolidation in major depression is impaired for procedural, but not declarative tasks. The same tasks in the awake state show a reversed pattern, with performance in declarative but not procedural tasks being impaired in major depression.