The lifetime prevalence of 15% for major depressive disorder (MDD) within the general population (1) is among the highest among all mental disorders. MDD is also one of the leading causes of disability and has been estimated to affect 300 million people worldwide (2, 3) and is associated with significant medical and psychosocial morbidity (4–7). Apart from symptoms of impaired mood, major depressive disorder is characterized by additional emotional, psychological, behavioral, physical, and cognitive symptoms, such as neuropsychological dysfunction (8, 9). According to the Diagnostics and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) (10), and the International Classification of Diseases (ICD-10) (11), cognitive symptoms of MDD are characterized by reduced concentration, memory deficits, and impaired decision-making processes. Cognitive dysfunction is not necessarily a symptom of aging with depression, but a symptom that may occur frequently across various cognitive domains in patients with first episode of depression and in young MDD patients (15–25 years of age) (12), in depression across all age groups, and during acute and remitted stages of the disorder (9).
