Do People With Depression Always Have Decreased Cognitive Processing Speed? Evidence through Electrophysiological Lens

Author(s): Daniel Kwasi Ahorsu, Hector WH Tsang

Decreased cognitive processing speed is a well-known deleterious effect of Major Depressive Disorder (MDD). Decreased cognitive processing speed which is closely related to psychomotor retardation is seen as one of the classical cognitive impairment among MDD patients. This, although true in most cases, does not apply to all cognitive processes of MDD patients who are exhibiting symptoms of psychomotor retardation. This review focuses on the cognitive processing speed of MDD patients without comorbidity as compared to their healthy counterparts with respect to emotion perception and intend to argue based on evidence that cognitive processing speed is not always slow in MDD patients. Results indicated that in general, there is longer reaction time (RT) or N170 latency to tasks among MDD patients as compared to healthy controls but MDD patients have shorter RT or N170 latency for sad facial stimuli (relative to happy) as compared to healthy controls. Recurrent episodes of MDD have worse cognitive processing speed which is reflected in the tasks having the shortest RT or N170 latency to sad facial stimuli (relative to neutral and happy) as compared to healthy controls. To conclude, the evidence supports the view that MDD patients may have developed a trait which makes them predisposed towards negative information, especially for sad facial stimuli. This may also be a reason to explain why their cognitive processing speed is observed to be faster in perceiving negative stimuli. Further studies are needed to ascertain the complexities of the information processing pathways in order to shed light on the development of more effective therapeutic strategies to mitigate the effects that are associated with it.

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