A method of treating a learning deficiency is disclosed wherein a patient in need of stimulating learning ability is treated with a therapeutically effective amount of a compound of the Formula (I) ##STR1## wherein R.sup.1 is C.sub.1 to C.sub.8 straight or branched chain alkyl, C.sub.7 to C.sub.10 phenylalkyl, phenyl, or C.sub.3 to C.sub.8 cycloalkyl; andR.sup.2 is C.sub.1 to C.sub.8 straight or branched chain alkyl, unsubstituted or substituted by halogen, hydroxy, C.sub.1 to C.sub.4 alkoxy or by 1 or 2 phenyl groups; or is C.sub.3 to C.sub.8 cycloalkyl;with the proviso that R.sup.1 and R.sup.2 together contain at least 3 carbon atoms; or a pharmaceutically acceptable salt thereof.