The hypothesis that processing speed deficits are the primary cognitive deficits in those with depression, consistent with the motor slowing hypothesis, was supported by a recent study, but only for depression burden and not diagnostic status or high vs low categorical classification. These results underscore the importance of validity assessment and consideration of how one measures psychiatric constructs when evaluating relations among symptoms and cognition. Participants (n=223) were research volunteers who served in the US military since September 11, 2001, and denied a history of significant brain injuries. Depression was measured using a structured interview, the Personality Assessment Inventory (PAI), and the Beck Depression Inventory-II (BDI-II). Researchers found:
- There was not a consistent pattern of slowed processing speed in those with current depressive diagnoses compared to those without.
- However, depression symptom burden per the PAI Depression scale was significant for 7 of 10 processing speed tests.
- Only non-dominant fine motor dexterity was significantly slower in those with high vs low burden using BDI-II quartiles.
Shura RD, Rowland JA, Martindale SL, Brearly TW, Delahanty MB, Miskey HM. Evaluating the motor slowing hypothesis of depression. [Published online ahead of print January 27, 2017]. Psychiatry Res. doi:10.1016/j.psychres.2017.01.074.