Evidence for the role of the arcuate fasciculus in language use is best represented by
conduction aphasia, caused by damage to the
inferior parietal lobule that extends into the subcortical white matter and damages the arcuate fasciculus.
[7] This type of
aphasia inhibits the patient from repeating unfamiliar sounds. A study by Catani, Jones, and Ffytche (2005) provided the first anatomical evidence for the presence of two pathways between Wernicke’s area and Broca’s area.
[8][9] They found one deep pathway, interpreted to directly connect these two regions, and a shallower pathway that consists of two segments; the anterior segment connects frontal cortex with inferior parietal cortex, and the posterior segment connects Wernicke’s area with the inferior parietal cortex. Damage to the direct pathway may produce
conduction aphasia, whereas damage to the indirect pathway spares the ability to repeat speech but impairs comprehension. The symptoms of
conduction aphasia suggest that the connection between posterior temporal cortex and frontal cortex plays a vital role in short-term memory of words and speech sounds that are new or have just been heard.
The arcuate fasciculus connects these two regions and circulates information back and forth, possibly contributing to short-term memory.
In nine out of ten people with
tone deafness, the superior arcuate fasciculus in the right hemisphere could not be detected, suggesting a disconnection between the posterior superior temporal gyrus and the posterior inferior frontal gyrus. Researchers suggested the posterior superior temporal gyrus was the origin of the disorder.
