Objective cognitive assessment
memory, learning memory, Rey Auditory Verbal Learning Test (RAVLT)
OC was measured through a comprehensive neuropsychological battery administered by two trained neuropsychologists lasting 45 to 60 min. The battery included the following tests: Digit Span Forward and Backward from the Wechsler Adult Intelligence Scale, 3rd edition (WAIS-III; Wechsler, 1999); Spatial Score Forward and Backward from the Wechsler Memory Scale, 3rd edition (WMS-III; Wechsler, 2004); Rey Auditory Verbal Learning Test (RAVLT); 10/36 Spatial Recall Test (SPART); Stroop Color and Word Test (SCWT); Trail Making Test (TMT) part A and B (for participants with low educational level, we used Color Trails Test, CTT); and phonetic verbal fluency (FAS). To estimate premorbid IQ, we used the Spanish version of the National Adult Reading Test (NART) (for participants with low educational level, we used the Vocabulary subtest of the Wechsler Adult Intelligence Scale, 4th edition, WAIS-IV) (see references in Additional file For the purposes of this study, raw scores from all cognitive tests were transformed into z-scores (mean = 0; SD =  ± 1) using the normative population data provided for each test, correcting the effects of age and education. Subsequently, seven cognitive indexes were calculated: attention, working memory, learning memory, delayed recall, memory recognition, processing speed and executive functions (see Additional file 