A method for delivering a biologic to a human with Alzheimer's-related dementia, comprising administering the biologic parenterally into the perispinal space of the human without direct intrathecal injection, and thereafter positioning the human's head below the horizontal. The method further includes delivering a TNF antagonist to the brain of a human for treating mild cognitive impairment, Alzheimer's related dementia, or vascular dementia, comprising administering the TNF antagonist golimumab parenterally into the perispinal space of the human without direct intrathecal injection, and thereafter positioning the human in a Trendelenburg position, for delivery of the golimumab to the brain via the human's vertebral venous system.