Aphasiology is the study of linguistic problems usually resulting from brain damage, as a result of a stroke or progressive illness including the various types of dementia. It is also the name of a scientific journal covering the area. These specific language deficits, termed aphasias, may be defined as impairments of language production or comprehension that cannot be attributed to trivial causes such as deafness or oral paralysis. A number of aphasias have been described, but two are best known:  Expressive aphasia (Broca's aphasia) and Receptive aphasia (Wernicke's or sensory aphasia).