Phenyl-3-aminoalkyl-4-methyl-2,6-dioxopiperidines of the Formula I ##STR1## wherein: R.sub.1 represents hydrogen or C.sub.1 -C.sub.4 alkyl;n is 1 or 2;R.sub.2 represents hydrogen or methyl, provided that one R.sub.2 is hydrogen when n is 2;R.sub.3 represents hydrogen or C.sub.1 -C.sub.2 alkyl;R.sub.4 represents C.sub.1 -C.sub.2 alkyl;R.sub.5 and R.sub.6 independently represent hydrogen or methyl;m is 0 to 3; andeach Y is in a meta or para position and independently represents hydroxy, C.sub.1 -C.sub.2 alkoxy, C.sub.1 -C.sub.2 alkyl, C.sub.1 -C.sub.2 hydroxyalkyl, halogen, or trifluoromethyl, provided that hydroxy and alkoxy are not in the para position,and not pharmacologically acceptable salts thereof have memory enhancing activity and are particularly useful in the treatment of cognitive deficiencies such as senile dementia.The presently preferred compound is 3-(3'methoxyphenyl)-3-(3'-N,N-dimethylaminopropyl)-4,4-dimethyl-2,6-dioxopiperidine (AGN 2979).