or without adjuvant antipsychotics vs. those who had not received any medication. Medication history, medication dosage, and duration of use were unknown. Nonetheless, these coarsely defined medication groups enabled better case-control discrimination and good classification of medicated vs. unmedicated cases. Fourth, there is a lack of information on OCD subtypes in our dataset. Particular OCD subtypes may have different neural correlates, and this might limit the ability of MVPA models to find generalizable patterns in brain structure14,50. Fifth, it should be noted that the age cut-off used to split the data in pediatric (age below 18) and adult (age 18 and older) samples may not be optimal with respect to the development of the brain, but this was done in accordance with the initial collection of pediatric and adult samples and previous ENIGMA work51,52. Finally, it is possible that the brain features used for classification led to sub-optimal performance. OCD is thought to derive from abnormalities distributed at the network-level rather than focused on a single brain area, and FreeSurfer features might not be sufficiently sensitive to detect subtle alterations associated with OCD.
