Northwestern researchers are peering inside the mind to map how we speak, listen to, and comprehend language.
Borna Bonakdarpour, neurology, is particularly interested in what happens in the brain when words seem to get stuck on the tip of the tongue. He also explores agrammatism, a condition where people maintain word comprehension but are unable to speak in a grammatically correct way.
Using functional magnetic resonance imaging (fMRI), the physician-scientist studies the brain’s language network in patients who have suffered a stroke or who are afflicted by primary progressive aphasia (PPA), a degenerative disease.
Both illnesses impede the normal neural pathways that words take: stroke does so with lesions; PPA by thinning the brain’s cortex or outer layer.
But neurons can fight back, as Bonakdarpour explains, because they are equipped with their own GPS-like function. When signals take a wrong turn, they can often be rerouted, relying on other, healthy parts of the brain to reach their final destination.
“The brain is an accommodating organ and when something goes wrong, it has the potential to try to regain function,” says Bonakdarpour, a member of Northwestern’s Cognitive Neurology and Alzheimer’s Disease Center. “One of our goals is to design interventions — pharmacological or otherwise — that help the language network reconnect around an injured area to once again communicate with less impediment.”
Bonakdarpour was among the first Northwestern researchers to use fMRI — more than a decade ago — to identify brain regions that are important in language production. That research team was able to show how aphasia disrupts such regions, producing difficulties in speaking, comprehending, reading, and writing language without affecting intelligence.
Bonakdarpour explores language processing using imagery and data collected from research participants who complete several tasks — word identification, for instance — while inside an MRI scanner. Brain activity is measured by detecting changes associated with oxygenated blood flow.
“fMRI looks at how brain cells consume oxygen as a proxy for how the brain functions,” says Bonakdarpour. “When people are processing a task in the scanner, they consume more oxygen in areas involved in processing of the task, and the increased profusion can be seen.” The technique is currently only used in a research capacity, though Bonakdarpour believes it will be adapted and eventually reach the clinic.
Because part of his week is spent seeing patients at Northwestern Memorial Hospital, Bonakdarpour entrusts research assistant Allan Wang, a junior studying neuroscience and philosophy, to analyze data and move the project forward.
“What I find most interesting about our lab work are the practical applications that our results could have on the diagnosis or treatment of neurodegenerative disorders,” says Wang. “I recently shadowed Dr. Bonakdarpour in his clinic and was able to talk to an individual with primary progressive aphasia. Being able to put a face with the MRI scans was really valuable and quite eye opening.”
One of Bonakdarpour’s earliest neuroimaging studies at Northwestern involved using music to help retrain neurons to connect in a meaningful way. He used CT scanning — a collection of x-ray images — to show that non-pharmacological intervention, which took advantage of the overlapping brain networks for language and music, could improve communication in patients with stroke-induced aphasia.
As a trained pianist, the combination of art and science is what led Bonakdarpour to join the lab of Cynthia Thompson, communication sciences and disorders, as a postdoctoral fellow. Today he counts Thompson among his many collaborators.
More recently, Bonakdarpour has worked with Robert Hurley and Marek-Marsel Mesulam, both neurology, to define important nodes of the language network in healthy people by using resting-state fMRI. Bonakdarpour has also used this tool to show how aphasia disrupts the language network in PPA patients.
“Even at rest, the areas of the brain that work together have a connectivity that can be seen using this newer technique,” says Bonakdarpour. “Using resting state fMRI, we saw how the front and back portions of the language network interact and how these are disrupted in individuals with PPA.”
Based on their findings, Bonakdarpour and colleagues proposed a new resting-state fMRI model for language processing. The researchers separated the language network into three nodes and two streams. Instead of relying on the long-held theory that the back part of the brain manages language comprehension and the front part deals with language production, the investigators revealed a new model.
They showed how disruption of the upper stream in PPA is related to sentence production, while disruption in the lower stream impacts naming and word-level processing.
“By better understanding the language network and increasing the functionality of fMRI, we can better design and monitor treatments to make a real impact for patients,” says Bonakdarpour. “PPA has no cure, but we hope to isolate the brain regions that are correlated with the language dysfunction and then develop a treatment that stymies the disease.”
Bonakdarpour will use a National Institutes of Health career development award to continue to pursue PPA research breakthroughs.