An agent for use in the prophylaxis or therapy of delirium comprising a compound selected from N-[2-(2-methyl-6,7-dihydro-8H-indeno[5,4-d][1,3]oxazol-8-ylidene)ethyl]acetamide, N-[2-(2-methyl-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]acetamide, N-[2-(2-methyl-6,7-dihydro-8H-indeno[5,4-d][1,3]oxazol-8-ylidene)ethyl]propionamide, N-{2-[2-(4-phenylbutyl)-6,7-dihydro-8H-indeno[5,4-d][1,3]oxazol-8-ylidene]ethyl}acetamide, N-[2-(2-methyl-6,7-dihydro-8H-indeno[5,4-d][1,3]thiazol-8-ylidene)ethyl]acetamide, N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]acetamide, -N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl] acetamide, -N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]acetamide, N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]propionamide, -N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]propionamide, -N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]propionamide, N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]thiazol-8-yl)ethyl]acetamide, -N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]thiazol-8-yl)ethyl] acetamide, -N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]thiazol-8-yl)ethyl]acetamide, N-[2-(2-ethyl-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]acetamide, -N-[2-(2-ethyl-7,8-dihydro-6H-indeno[5,4-d] [1,3]oxazol-8-yl)ethyl]acetamide, -N-[2-(2-ethyl-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]acetamide, N-[2-(2-methoxy-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]acetamide, -N-[2-(2-methoxy-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]acetamide, and -N-[2-(2-methoxy-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]acetamide or a salt thereof as an active ingredient. N-[2-(2-methyl-6,7-dihydro-8H-indeno[5,4-d][1,3]oxazol-8-ylidene)ethyl]acetamide, N-[2-(2-methyl-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]acetamide, N-[2-(2-methyl-6,7-dihydro-8H-indeno[5,4-d][1,3]oxazol-8-ylidene)ethyl]propionamide, N-{2-[2-(4-phenylbutyl)-6,7-dihydro-8H-indeno[5,4-d][1,3]oxazol-8-ylidene]ethyl}acetamide, N-[2-(2-methyl-6,7-dihydro-8H-indeno[5,4-d][1,3]thiazol-8-ylidene)ethyl]acetamide, N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]acetamide, -N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl] acetamide, -N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]acetamide, N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]propionamide, -N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]propionamide, -N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]propionamide, N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]thiazol-8-yl)ethyl]acetamide, -N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]thiazol-8-yl)ethyl] acetamide, -N-[2-(2-methyl-7,8-dihydro-6H-indeno[5,4-d][1,3]thiazol-8-yl)ethyl]acetamide, N-[2-(2-ethyl-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]acetamide, -N-[2-(2-ethyl-7,8-dihydro-6H-indeno[5,4-d] [1,3]oxazol-8-yl)ethyl]acetamide, -N-[2-(2-ethyl-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]acetamide, N-[2-(2-methoxy-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]acetamide, -N-[2-(2-methoxy-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]acetamide, and -N-[2-(2-methoxy-7,8-dihydro-6H-indeno[5,4-d][1,3]oxazol-8-yl)ethyl]acetamide