Looking for visual cortical activity as putative brain biomarker: a pilot fNIR study on autistic female preschoolers. We performed an observational prospective monocentric study in a tertiary care University hospital (IRCCS Stella Maris Foundation, Pisa, IT). We recruited 12 females with idiopathic ASD and 13 sex/age-matched control typically developed peers. Established inclusion criteria were: 1) diagnosis of ASD according to the DSM-5 criteria (APA, 2013); 2) age range: between 3 and 6 years; 3) female gender; 4) negative genetic testing for Fragile X and MECP2; 5) negative history of premature birth or neurologic complications possibly related to delivery and 6) non-verbal IQ > 70. ASD diagnosis has been performed by a multidisciplinary team including a senior child psychiatrist, an experienced clinically trained research child psychologist and a speech-language pathologist during 5-7 days of extensive evaluation. Demographic characteristics and clinical features of experimental cohorts are listed in Tables 1 and 2. Clinical measures such as Autism Diagnostic Observation Schedule (ADOS) (Lord et al., 2012), Autism Questionnaire (AQ) – children’s version, cognitive and adaptive profile were systematically collected for each subject using internationally validated scales/interviews, such as Wechsler Preschool and Primary Scale of Intelligence (Wechsler, 2002) and Vineland Adaptive Behavior Scales-II –VABS- (Sparrow et al., 2005). All participants reported normal or corrected-to-normal vision.