Wernicke's area · Grey Matter

Wernicke's area is the back part of the left superior temporal gyrus that links the sounds of words to their meaning: it is needed to understand spoken language and to choose the right words when speaking.

Wernicke's area. Wernicke's area is the back part of the left superior temporal gyrus that links the sounds of words to their meaning: it is needed to understand spoken language and to choose the right words when speaking.

It lies behind the primary auditory cortex, in the posterior part of Brodmann area 22, reaching into the planum temporale. Carl Wernicke described it in 1874 from patients who spoke fluently but made little sense and understood little of what was said to them. Its boundaries are less agreed than Broca's, and modern accounts treat it as part of two streams. A ventral stream along the temporal lobe maps sounds onto meanings (comprehension). A dorsal stream, through the parietal-temporal junction and the arcuate fasciculus to Broca's area, maps sounds onto the movements that produce them, which is what repeating a heard word requires.

Damage here gives Wernicke's aphasia: speech flows with normal rhythm but is full of wrong or invented words, and comprehension fails.

The left planum temporale is larger than the right in most brains, one of the anatomical asymmetries behind language lateralisation.

Early processing of speech sounds is bilateral; the left dominance grows as the processing moves toward meaning and articulation.

Questions: Why does damage to Wernicke's area leave speech fluent but full of wrong words? The frontal machinery that produces the rhythm, melody and grammar of speech is intact, so words keep coming at a normal rate. What is lost is the region that links word sounds to their meanings and checks what is about to be said against what was meant, so the wrong sounds and the wrong words get through: paraphasias, invented words, sometimes jargon. The same damage breaks comprehension of others' speech, and because the patient's own monitoring is broken too, many are unaware that they are not making sense. How can someone hear sounds normally and still not recognise speech or a ringing phone? Hearing tests check whether a tone is detected, which needs only the ear and the early auditory pathway. Recognising a sound as a word, a voice or a phone needs the auditory association cortex of the temporal lobe, and damage there (usually on both sides, or on the left together with the fibres from the right) leaves sounds heard but meaningless, a rare condition called auditory agnosia. When only speech is affected it is called pure word deafness: the patient hears that someone is talking, can read and write, and cannot understand what is said. How do Broca's and Wernicke's areas work together when you repeat a word you just heard? The heard word is analysed in the auditory cortex and the superior temporal gyrus, both sides contributing. To repeat it, a left-dominant dorsal stream maps the sound onto the movements that would produce it, through the temporoparietal junction and the arcuate fasciculus to the inferior frontal cortex and premotor areas. A ventral stream along the temporal lobe meanwhile maps the sound onto its meaning, which is what understanding needs. Damage to the dorsal link with both ends spared gives conduction aphasia, in which repetition fails out of proportion to speaking and understanding.