The present invention relates to the use in the treatment of cognitive disorders associated with the aging processes of the brain and perinatal brain disorders of compounds which act as inhibitors of the enzyme kynurenine aminotransferase (KAT). The present invention also provides, as novel compounds, a selected class of KAT inhibitors which are the compounds of formula (IA) ##STR1## wherein R is halogen, C.sub.1 -C.sub.6 alkyl, C.sub.5 -C.sub.7 cycloalkyl, phenyl-C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.6 alkoxy, C.sub.6 -C.sub.10 aryloxy, phenyl-C.sub.1 -C.sub.4 alkoxy or trifluoromethyl, and R.sub.1 is hydroxy, C.sub.1 -C.sub.6 alkoxy, amino, mono-C.sub.1 -C.sub.6 alkylamino, di-C.sub.1 -C.sub.6 alkylamino, hydroxylamino, C.sub.1 -C.sub.4 alkoxyamino or benzyloxyamino, with the provisos that: (i) when R.sub.1 is hydroxy and, at the same time, R is halogen, then this halogen is not fluorine; and (ii) when R.sub.1 is hydroxy and, at the same time, R is C.sub.1 -C.sub.6 alkyl, then this C.sub.1 -C.sub.6 alkyl is not methyl, either as a single isomer or as a mixture of isomers, and the pharmaceutically acceptable salts thereof.