December 13, 2016 | Erin Bluvas, bluvase@sc.edu
A team of researchers* led by Communication Sciences and Disorders (COMD) Professor Julius Fridriksson has completed the first comprehensive study that reveals human speech processing relies on a dual stream system in the brain. Published in Proceedings of the National Academy of Sciences, a top scientific journal, the study provides empirical evidence of the dual streams theory to speech and language processing.
The researchers found distinct anatomical boundaries between the two streams described in this theory: speech production/articulation (dorsal fronto-parietal stream) and speech comprehension (ventral temporal-frontal stream). By revealing the division between the two processing routes that underlie human speech processing, the team has provided a scientific foundation for studying further functional differences between and features of the two routes.
Studying these streams holds implications for those who have experienced brain injury (e.g., stroke/car accident survivors) and have subsequent communication challenges—namely more accurate prognosis and customized treatment plans. The researchers were also able to use brain mapping to identify regions crucial for performance on behavior tasks. These insights are crucial to improving treatment and outcomes for stroke survivors and others who have experienced brain injuries.
“Damage to these streams causes specific patterns of behavioral impairments that can be dissociated depending on the location of the brain damage,” says Fridriksson. “The extent of damage to these processing streams is probably associated with negative prognosis following brain damage.”
While there are several proposed models for how speech and language processing are organized in the brain, the dual streams theory is a favorite among scientists. Though largely theoretical up until now, the dual streams approach has now been supported by the researchers’ present study using neuroimaging and behavioral assessment data from a sample of 138 stroke survivors.
“In spite of these models, no comprehensive study has completely revealed the dual streams that support speech processing in the brain,” says Fridriksson. “Relying on a large sample of patients who underwent extensive behavioral testing and brain imaging, we were able to map out the dual streams that support speech processing in humans.”
By offering empirical support for the theory, the study has opened the door to future research. “This study has major implications for understanding the fundamental differences across the two streams that enable processing and sets the tone for further research in this area,” says Fridriksson. “Future research should attempt to understand the functional interactions between the two main processing streams in the brain and how this interaction gives rise to human speech processing.”
This study was conducted through Fridriksson’s C-Star Center for the Study of Aphasia Recovery using grants from The National Institute on Deafness and Other Communication Disorders (DC008355, DC009571, and DC014664). Fridriksson also directs the Aphasia Lab and co-directs the McCausland Center for Brain Imaging. He is the SmartState Endowed Chair for Memory and Brain Function for the SeniorSMART Center of Economic Excellence.
*Additional co-authors on the study include Grigori Yourganov (Psychology), Leonardo Bonilha (Medical University of South Carolina), Alexandra Basilakos (Communication Sciences and Disorders), Dirk-Bart den Ouden (Communication Sciences and Disorders), Chris Rorden (Psychology)
Related:
Julius Fridriksson named S.C. SmartState Endowed Chair of Memory and Brain Function