Neuroscientists at Georgetown University Medical Center say the brain's auditory lexicon, a catalog of verbal language, is located in front of the primary auditory cortex, not behind it - a finding that challenges previous understanding of this area of the brain. These new results may impact recovery and rehabilitation strategies following a brain injury such as a stroke.
The findings appear in Neurobiology of Language. The work was supported in part by the U.S. National Science Foundation. The research also used NSF-supported advanced computing currently coordinated through ACCESS.
Previous studies have shown the existence of a lexicon for written words at the base of the brain's left hemisphere in a region known as the Visual Word Form Area. The researchers determined that newly learned written words are added to this area. The present study sought to test whether a similar lexicon exists for spoken words in a corresponding Auditory Word Form Area, located in front of the primary auditory cortex.
"Since the early 1900s, scientists believed spoken word recognition took place behind the primary auditory cortex, but that model did not fit well with many observations from patients with speech recognition deficits, such as stroke patients," says Maximilian Riesenhuber, a neuroscientist at Georgetown University Medical Center and senior author of the study. "Our discovery of an auditory lexicon more toward the front of the brain provides a new target area to help us understand speech comprehension deficits."
Volunteers went through three rounds of non-invasive functional magnetic resonance imaging scans to examine their spoken-word processing abilities. The technique used is called functional-MRI rapid adaptation, which is more sensitive than conventional fMRI in assessing representation of auditory words as well as in the learning of new words. In future studies, the researchers hope to investigate how interventions aimed at the Auditory Word Form Area affect speech comprehension in people who have suffered strokes or brain injuries.
