Terrence Murgallis, a 20 year-old undergraduate student in the Department of Speech-Language Pathology at Misericordia University has stuttered all his life and approached us recently about conducting brain research on stuttering. His timing was perfect because our research group, in collaboration with a team led by Dr. Arjun Yodh in the Department of Physics and Astronomy at the University of Pennsylvania, had recently deployed two novel optical methods to compare blood flow and hemoglobin concentration differences in the brains of those who stutter with those who are fluent.
These noninvasive methods employ diffusing near-infrared light and have been dubbed near-infrared spectroscopy (NIRS) for concentration dynamics, and diffuse correlation spectroscopy (DCS) for flow dynamics. The near-infrared light readily penetrates through intact skull to probe cortical regions of the brain. The low power light has no known side-effects and has been successfully utilized for a variety of clinical studies in infants, children, and adults.
DCS measures fluctuations of scattered light due to moving targets in the tissue (mostly red blood cells). The technique measures relative changes in cerebral blood flow. NIRS uses the relative transmission of different colors of light to detect hemoglobin concentration changes in the interrogated tissues. Though there are numerous diagnostic tools available to study brain activity, including positron emission tomography (PET), magnetic resonance imaging (MRI), and magnetoencephalography (MEG), these methods are often invasive and/or expensive to administer. In the particular case of electroencephalography (EEG), its low spatial resolution is a significant limitation for investigations of verbal fluency.
Our initial results (Tellis et al., 2011), in persons who stutter and in normally fluent speakers (figure 1), suggest that speech tasks induce hemodynamic changes in parts of the brain that control speech, including Brocas area and pre-frontal regions. We observed a greater amount of blood flow in Brocas area when compared to the pre-frontal region in all subjects; however, in normally fluent speakers, a greater increase in blood flow to Brocas area was observed compared to persons who stutter.
This trend suggests a possible speech-related difference for comparing the two populations during speaking tasks. Like flow, total hemoglobin concentration increased in Brocas area and in the pre-frontal cortex during most speech tasks we studied, but unlike flow, these changes were similar for both persons who stutter and normally fluent speakers. Interestingly, for two tasks, i.e., free speech and choral speech, a decrease in total hemoglobin concentration was exhibited by persons who stutter.
Now, Terrence has an even greater cause to be excited about brain studies. President Obama, in his 2013 State of the Union address, announced that his administration aims to fund scientists to map the human brain and thereby unlock the mysteries of memory, learning, and thinking. Our research, as well as research by others, indicates that the diffuse optical methodologies are attractive for determining differences in cerebral blood flow and blood oxygenation levels during speech tasks.
Ultimately, progress along these lines could lead to improved diagnostic and treatment techniques for persons with speech and language disorders, including stuttering. Our strategy going forward is to obtain a large amount of baseline data for typical speech and language patterns. Then, we plan to then apply these same technical paradigms to test those with disorders of speech and language including stuttering, voice, articulation, language, autism, aphasia, apraxia, dysarthria, and other conditions. These technologies are thus expanding our knowledge of the brain and could even improve upon the care we provide to clients.
Tellis, G. M., Mesquita, R., & Yodh, A. (2011). Using diffuse correlation spectroscopy to measure brain blood flow differences during speaking and nonspeaking tasks for fluent speakers and persons who stutter. Perspectives on Fluency and Fluency Disorders, 21(3), 96-106.