Aphasia

Aphasia, the loss of power of speech, arising not from a lack of ideas, nor from any defect in the muscles of the larynx, tongue, etc., but from an interference with the functions of the so-called speech centre in the brain. This centre is situated in the lower and hinder portion of the frontal lobe of the brain on the left side; it is known as Broca's centre, being named after the man who first insisted upon the relation of this part of the brain to speech. It is a well established fact that the left side of the brain is associated with movements of the right side of the body, and consequently interference with the speech centre is commonly accompanied by paralysis of the right arm and leg. The most common cause of aphasia is some interference with the circulation of blood through the middle cerebral artery which supplies Broca's centre; either by rupture of the vessel, or by its becoming acclouded by disease. Thus aphasia is a common symptom in apoplexy (q.v.), being then associated with right hemiplegia (q.v.). Aphasia may be partially recovered from, either by the re-establishment of the functions of Broca's centre, or, in other cases where that part of the brain is irreparably damaged, it is supposed that the corresponding portion of brain on the right side is capable of taking on the functions of a centre for speech.