Therapeutic agent for senile dementia

A therapeutic/preventive agent for cognitive dysfunctions, which comprises as an active ingredient an imide derivative of the formula [1]:

• {wherein Z is a group of the formula [2]:
• (in which B is a carbonyl or a sulfonyl;
• R1 R2, R3 and R4 are independently a hydrogen atom or a lower alkyl, provided that R1 and R2, or R1 and R3 may combine each other to form a hydrocarbon ring, or R1 and R3 may combine each other to form an aromatic hydrocarbon ring;
• said hydrocarbon ring may optionally be cross-linked with a lower alkylene or an oxygen atom;
• said lower alkylene and hydrocarbon ring may optionally be substituted by at least one alkyl;
• and n is 0 or 1), D is a group of the formula [3]:
• —(CH2)p—A—(CH2)q— [3] (in which A is a hydrocarbon ring optionally be cross-linked with a lower alkylene or an oxygen atom;
• said lower alkylene or said hydrocarbon ring may optionally be substituted by at least one alkyl;
• and p and q are independently 0, 1 or 2), G is N, CH or COH, and —Ar is an aromatic heterocyclic group, an aromatic hydrocarbon group, benzoyl, phenoxy, or phenylthio, or G is a carbon atom, and —Ar is biphenylmethylidene, where said aromatic heterocyclic group, aromatic hydrocarbon group, benzoyl, phenoxy, phenylthio, and biphenylmethylidene may optionally be substituted by at least one group selected from a lower alkyl, a lower alkoxy and a halogen atom}, or an acid addition salt thereof.