Depression in late life follows a relapsing course and it has been related to impaired cognitive control. Information processing speed, memory and executive abilities are most frequently impaired.

Cognitive changes are difficult to confirm during depressive episode, as signs of both disorders largely overlap. Therefore, it makes more sense to assess cognition after a remission has been reached. Electrophysiology may be particularly convenient as a tool in such studies, as it can separate central cognitive processing from the motor processing.

The study of cognition was focused on executive function and speed of information processing. It was measured with Stroop-related event related potentials (ERPs) and reaction times (RTs) in a modified computer version of the Stroop test which is highly sensitive to frontal functions.

Thirty-four patients with late-onset depression were included after they had reached remission. They were compared to twenty-four age-, gender- and education-matched healthy controls. Each participant completed a single item computer version of the Stroop task using verbal response mode. EEG and RT were simultaneously recorded.

Revealed abnormal late positive Stroop-related potentials in the period of about 500–600ms period corresponding to the latency of the so-called P300b wave.

Study supports the view that patients with late onset depression are also cognitively impaired and that this impairment persists in the period of early remission. Using more sensitive ERP measurement of the Stroop task, we demonstrated impaired information processing at an earlier, pre-response related stage.