Abstract: Compounds of the formula I ##STR1## wherein R.sub.1 represents ##STR2## and the remainder of the variables are defined in the specification are useful in the treatment and/or prophylaxis of dementia in mammals.

Abstract: Azabicyclic compounds, processes for their preparation and their use in the treatment and/or prophylaxis of dementia in animals.

Abstract: A compound of formula (I) or a pharmaceutically acceptable salt thereof: ##STR1## in which one of X and Y represents hydrogen and the other represents Z, where Z is a group ##STR2## in which Q represents a 3-membered divalent residue completing a 5-membered aromatic ring and comprises one heteroatom selected from oxygen, nitrogen and sulphur or two heteroatoms selected from sulphur and nitrogen, any amino nitrogen being optionally substituted by a C.sub.1-2 alkyl, and at least one ring carbon atom being substituted by a group R.sub.1 ; or a group ##STR3## in which A.sub.1, A.sub.2 and A.sub.3 complete a 5-membered aromatic ring and A.sub.1 is oxygen or sulphur, A.sub.2 is CR.sub.2 and A.sub.3 is nitrogen or CH, or A.sub.2 is oxygen or sulphur, A.sub.1 is CH and A.sub.3 is CR.sub.2 ; and R.sub.1 and R.sub.2 are selected from, halogen, CN, OR.sub.4, SR.sub.4, N(R.sub.4).sub.2, NHCOR.sub.4, NHCOOCH.sub.3, NHCOOC.sub.2 H.sub.5, NHOR.sub.4 NHNH.sub.2, NO.sub.2, COR.sub.4, COR.sub.5, C.sub.2-4 alkenyl, C.sub.