On the other hand, human studies exploring tDCS-induced effects on BDNF levels provided contrasting results, with some reports of unmodified peripheral BDNF levels after tDCS intervention (Marangolo et al., 2014; Brunoni et al., 2015) and other reports of alterations in BDNF levels in different neurological and psychiatric conditions, such as Parkinson's disease and schizophrenia (Hadoush et al., 2018; Adam et al., 2021). Here, BDNF is linked to schizophrenia.