Wernicke's aphasia · Grey Matter

Wernicke's aphasia is a disorder of language comprehension after damage to the back of the left superior temporal gyrus, in which speech stays fluent and well articulated but loses its sense, and understanding of what others say breaks down.

Wernicke's aphasia. Wernicke's aphasia is a disorder of language comprehension after damage to the back of the left superior temporal gyrus, in which speech stays fluent and well articulated but loses its sense, and understanding of what others say breaks down.

Patients speak at a normal rate and melody, with grammar that sounds intact, but the words are wrong: sounds are swapped (phonemic paraphasias), related words replace the intended ones (semantic paraphasias) and invented words appear (neologisms), sometimes to the point of jargon. Comprehension of spoken and written language is severely impaired, as are repetition and naming. Many patients are unaware of their errors (anosognosia), so they keep talking and may be puzzled or irritated that they are not understood.

The lesion sits in Wernicke's area, the posterior superior temporal gyrus of the dominant hemisphere, often reaching the parietal cortex around it; no movement deficit usually accompanies it, because the motor strip is spared.

Its contrast with Broca's aphasia made the classic model: production in front, comprehension behind, a fibre bundle between them.

Damage to the bundle that links them, sparing both areas, gives conduction aphasia, in which comprehension and fluency are fair but repetition fails, a prediction of that model.

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.