For more than 100 years, it has been a scientific dogma that Wernicke's area is the seat of language comprehension in the human brain. However, a team of researchers recently discovered that the hotdog-shaped region in the temporal lobe of the left hemisphere is actually not.

In a study published in the neurology journal Brain, a team of researchers at Northwestern University have determined that Wernicke's area may not be the seat of language. According to The Scientist, understanding the meaning of words happens in the left anterior temporal lobe, which is a more forward location than Wernicke's. Sentence comprehension, on the other hand, is managed by a complex of brain areas instead of a single part of the brain as previously thought.

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"This provides an important change in our understanding of language comprehension in the brain," Northwestern's Cognitive Neurology and Alzheimer's Disease Center director and lead study author Dr. Marek-Marsel Mesulam stated.

In 1874, neuroscientist Carl Wernicke discovered that some stroke patients with damage in the left side of their brains suffered language impairment known as Wernicke aphasia. Since the patients could often speak clearly but senselessly, and had trouble comprehending simple information, Wernicke and other colleagues assumed that the patients' stroke had damaged the language comprehension center of the brain.

Based on the new research, however, scientists have updated and revised the traditional brain map of language comprehension through an experiment conducted with individuals who have a rare form of dementia known as Primary Progressive Aphasia (PPA), which affects language.

For years, Mesulam, who is the world's leading PPA expert, had been wondering over the fact that his PPA patients with damage in Wernicke's area did not appear to have the word comprehension impairment seen in stroke patients. They still understood individual words, however, their sentence comprehension was inconsistent.

Due to the inconsistencies in the textbooks and as seen in actual patients, Mesulam said that there's an obvious discrepancy from the view of the brain from stroke than from the view of the brain from PPA.

In order to analyze the discrepancy, experts began a study of PPA patients. Through conducting quantitative MRI imaging of the brains of PPA patients and testing their language, scientists were able to measure the cortex thickness, which is an indirect measure of the number of neurons and brain health.

The severe word comprehension loss was only seen in PPA patients who had diminished cortical thickness in a region of the brain completely outside of Wernicke's area. Since this part of the brain is in the front part of the temporal lobe, it is not prone to the effects of stroke.  So, BioScience Technology reported that its role in comprehension had been overlooked in previous language maps.

The discrepancy between the traditional map of comprehension and what was seen in PPA can be explained by the different ways the two diseases injure Wernicke's area. In PPA, the neurodegenerative disease does not damage the primary fiber pathways that allow language areas to work together.

In stroke patients, however, those critical highways passing through Wernicke's had been swollen. So, the messages from other parts of the brain to the left anterior temporal lobe, which is the area for word comprehension, were simply not getting through.

To sum up, scientists discovered a different language map by comparing two different models of the disease. One is based on strokes that destroy an entire region of the brain, cortex, and the primary pathway, while the other is based on a neurodegenerative disease that attacks mostly brain cells in the cortex instead of the region as a whole.  

Meanwhile, when a patient suffers a stroke, blood supply to regions of the brain is usually blocked, resulting to damages of both neurons and fiber pathways passing through that region. That's why knowing where language comprehension is located gives a more accurate target for future therapies that could potentially protect and restore language function, Eurek Alert has learned.

TagsBrain Language Map, Wernicke's Area, Science, brain, Study