Differentiating depression and ADHD without depression in adults with processing-speed measures.

Area of Science:

• Neuroscience
• Psychiatry
• Cognitive Psychology

Background:

• Cognitive impairments are common in depression and attention-deficit hyperactivity disorder (ADHD).
• Processing speed and executive functions, like cognitive flexibility (shift costs), are key areas of investigation.
• Objective measures are needed to differentiate these conditions and monitor treatment efficacy.

Purpose of the Study:

• To evaluate processing-speed and shift-cost measures in differentiating adults with depression and ADHD.
• To monitor the effects of treatment on these cognitive measures.
• To test the hypothesis that these measures can distinguish between diagnostic groups.

Main Methods:

• Assessed naming times for colour, form, and colour-form stimuli to calculate processing speed.
• Calculated shift costs as the difference between colour-form naming time and the sum of colour and form naming times.
• Measured cognitive performance at baseline and end-point in 42 adults with depression (treated with transcranial pulsed electromagnetic fields) and 42 with ADHD (treated with methylphenidate).

Main Results:

• Processing speed (colour-form naming times) and shift costs were sensitive in differentiating depression and ADHD groups at baseline.
• Naming times decreased in both groups after treatment.
• ADHD patients showed improved shift costs after stimulant medication, returning to average-normal ranges, while depression patients' shift costs remained in the average-normal range throughout.

Conclusions:

• Pre-treatment cognitive-processing-speed (colour-form) and shift-cost measures are most effective in differentiating patients with depression and ADHD.
• Observed reductions in naming times for the depression group may indicate improved psychomotor speed rather than enhanced cognitive control.