Cognitive functioning in young and middle-aged unmedicated out-patients with major depression: testing the effort and cognitive speed hypotheses.
BACKGROUND
Cognitive deficits are common in major depressive disorder, but their nature is unclear. The effort hypothesis states that performance on effortful tasks is disproportionately impaired compared with the performance on automatic tasks. The cognitive speed hypothesis states that depression is characterized by cognitive slowness, which is a source of cognitive dysfunctioning. The present study investigated both theories in unmedicated adult depressive patients. It was also investigated whether the cognitive deficits can be attributed to more general physical illness-related factors or specifically to depressive disorder.


METHODS
Thirty non-psychotic depressive out-patients were compared with 38 healthy control subjects and 25 patients with severe allergic rhinitis. The effects of group on more automatic and more effortful aspects of cognitive tasks measuring cognitive speed (Concept Shifting Task, Stroop Colour Word Test, Memory Scanning Test) and memory retrieval (Visual Verbal Learning Task, Verbal Fluency Test) were evaluated by MANCOVA. Age, sex, education and pre-morbid intelligence were treated as covariates.


RESULTS
The depressive group had cognitive deficits in the automatic processing subtask of the Stroop, memory scanning and memory span. Performance on more effortful tasks was not impaired.


CONCLUSIONS
Our results are more consistent with the cognitive speed hypothesis. Cognitive functioning in depressive disorder seems to be characterized by a reduced speed of information processing in automatic subtasks.
Den Hartog
H M
HM
Department of Psychiatry and Neuropsychology, Maastricht University, Maastricht, The Netherlands.
Derix
M M A
MM
Van Bemmel
A L
AL
Kremer
B
B
Jolles
J
J
D000328:Adult; D000367:Age Factors; D001288:Attention; D003072:Cognition Disorders / Q000175:diagnosis* / Q000523:psychology; D003118:Color Perception; D003430:Cross-Sectional Studies; D003865:Major Depressive Disorder / Q000175:diagnosis* / Q000523:psychology; D004193:Discrimination Learning; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests / Q000706:statistics & numerical data*; D005082:Physical Exertion; D011594:Psychometrics / Q000706:statistics & numerical data; D011930:Reaction Time; D012016:Reference Values; D015203:Reproducibility of Results; D012221:Rhinitis, Allergic, Perennial / Q000523:psychology; D006255:Rhinitis, Allergic, Seasonal / Q000523:psychology; D012660:Semantics; D012803:Sick Role; D014706:Verbal Learning