Brain and Language: New Insights About Processing of Spoken Words

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Highlights:

• Researchers have found the front of the primary auditory cortex in the brain is mainly involved in processing spoken words, contrary to long-held beliefs
• This unexpected location was found using a functional MRI rapid adaptation technique, more sensitive than conventional functional MRI
• This could contribute to a better understanding of speech comprehension deficits and help in the recovery of brain injury

The auditory lexicon in the auditory word form area (AWFA) in the left anterior superior temporal gyrus of the human brain is the main area that catalogs verbal language, according to Georgetown University Medical Center neuroscientists.

This finding defies a century-long understanding of this area of the brain. It was believed that the brain's auditory lexicon is in the back of the primary auditory cortex. Now, the understanding of this area has been completely changed. The findings appear in Neurobiology of Language.

‘A discovery challenges the century-long assumption about language processing in the brain and could influence the rehabilitation of stroke and brain injury patients.#Language #Brain research #Linguistics’

Recognizing spoken words is important to daily life. Identifying the relevant neural computations and units over which they are performed is critical to furthering the understanding of how the brain performs this process.

Reconsidering Speech Recognition: An Unexpected Discovery in Brain's Auditory Lexicon

Previous research showed 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 (VWFA) and subsequently found that newly learned written words are added to the VWFA (1^✔).

In the new study, researchers sought to test whether a similar lexicon existed for spoken words in the so-called Auditory Word Form Area (AWFA), located anterior to the primary auditory cortex.

Scientists believed spoken word recognition took place behind the primary auditory cortex since the early 1990s, but that model did not fit well with many observations from patients with speech recognition deficits, such as stroke patients.

The unexpected discovery of an auditory lexicon more toward the front of the brain provides a new target area to help us understand speech comprehension deficits. It may also impact recovery and rehabilitation following a brain injury such as a stroke.

In the study, 26 volunteers underwent three rounds of functional magnetic resonance imaging (fMRI) scans to examine their spoken word processing abilities. This technique is more sensitive than conventional fMRI in assessing the representation of auditory words and the learning of new words.

This provided evidence for an auditory lexicon in the "Auditory Word Form Area" (AWFA) in the human left anterior superior temporal gyrus that contains representations highly selective for individual spoken words (2^✔). Furthermore, familiarization with new auditory words sharpens their selectivity in the AWFA.

Future studies should investigate how interventions directed at the AWFA, affect speech comprehension deficits in populations with different types of strokes or brain injury. Researchers are also trying to understand how the written and spoken word systems interact.

Beyond that, they are using the same techniques to look for auditory lexica in other parts of the brain, such as those responsible for speech production. This is important because many aspects of how the brain processes words, either written or verbal, remain unexplored (3^✔).

It is known that learning to speak relies on our auditory system which tells us whether the sound produced accurately represents the intended word. However, the brain's process for this remains poorly understood. This includes both young children learning to speak for the first time and older people learning a second language.

References:

1. The visual word form area (VWFA) is part of both language and attention circuitry - (https:www.nature.com/articles/s41467-019-13634-z)
2. Evidence for a Spoken Word Lexicon in the Auditory Ventral Stream - (https:direct.mit.edu/nol/article/doi/10.1162/nol_a_00108/116025/Evidence-for-a-Spoken-Word-Lexicon-in-the-Auditory)
3. Reading Comprehension Deficits in Adolescents: Addressing Underlying Language Abilities - (https:pubs.asha.org/doi/10.1044/2016_LSHSS-16-0048#)

Source: Medindia

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