The major characteristic that differentiates between delirium and dementia of Alzheimer’s type (DAT) is:

Choice A reason: Dementia, including Alzheimer’s type, is characterized by a slow, progressive cognitive decline without periods of full recovery or fluctuation, which differentiates it from delirium. Choice B reason: Delirium typically presents with acute onset and fluctuating cognition, not a gradual decline; this statement is incorrect. Choice C reason: Disturbances in the sleep-wake cycle are more characteristic of delirium and some types of dementia but are not the defining difference between delirium and Alzheimer’s dementia. Choice D reason: Dementia is usually chronic and progressive, and full recovery is rare; this statement is inaccurate.