An alkyl ether derivative represented by the formula: ##STR00001## wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, m and n are as defined in the specification, or salts thereof exhibits synergistically improved anti-hypoxic activity when combined with a compound having an acetylcholine esterase inhibitory activity. Therefore, the combination according to the present invention is useful as a method for improving cerebral function. Further, a pharmaceutical composition containing the compound relating to the combination according to the present invention is useful for treatment and prevention of dysfunction of cerebral acetylcholine neurons in the sequelae of cerebrovascular dementia, senile dementia, Alzheimer's disease and ischemic cerebral lesion and in the cerebral apoplexy or the memory impairment caused by selective neuronal death.