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The arcuate fasciculus is a bundle of nerve fibers that connects the temporal and parietal lobes of the brain, known as the temporoparietal junction (TPJ), to the frontal lobe. Also, it is considered one of the four components that comprise the superior longitudinal fasciculus (SLF). There is still debate, however, within the medical community regarding the exact areas of connection in the three aforementioned lobes. The arcuate fasciculus is a Latin term for "curved bundle."
Some neurologists believe that the arcuate fasciculus connects an area of the TPJ called Wernicke's area to an area of the frontal lobe referred to as Broca's area. Wernicke's area is used for recognizing or understanding speech, while Broca's area is used for speech production. Thus, the arcuate fasciculus, via connection of both areas, is believed to be instrumental in determining one's ability to speak and write.
Broca's area entered the medical lexicon in 1861 when French neurosurgeon Paul Broca examined the brain of a dead patient who had been unable to say a sentence and write down his thoughts. The patient, who had been named "tan" after the only articulate sound he was able to utter, had this disability despite being able to recognize speech. Tan was free from any speech impediments though.
After examining eight more patients, Broca confirmed the defect: a lesion in the left bottom area of the frontal lobe. This symbolized the first time in history that an area of the brain had been associated with language. Ten years later, in 1871, German neurologist Carl Wernicke discovered another area of the brain related to language, located in the rear portion of the temporal lobe's left side. He noted that people with a lesion at this area could produce speech, but their speech was hard to understand.
Thus, with time, neurologists theorized that there had to be a neural pathway connecting Wernicke's area with Broca's area. It was believed that such a connection enabled people to not only speak, but to do so coherently. That neural pathway, consisting of white matter for connecting areas of the nervous system relatively distant from each other, is called the arcuate fasciculus.
Other neurologists, however, challenge the arcuate fasciculus theory regarding language processing. Due to recent neuroradiological studies, some researchers contend that the bundle connects rear-located receptive areas with premotor/motor ones instead of Broca's area. It is generally agreed, however, that the arcuate fasciculus provides a connection between the temporal, parietal and frontal lobes of the brain.