For almost two decades, neuroscientists have been able to examine patterns of activity in the brain using functional magnetic resonance imaging (fMRI). This technique uses the magnetic signature of oxygen in blood as a proxy for neuronal activity in the brain. FMRI allows us to see activation in the brain as a result of a task constructed in the lab, and to discern which areas of the brain “do” certain things.
Until this point, few people have been able to change brain activity in healthy participants. However, recent advances in neuroscience have made it possible to modulate brain activity. Research in Catherine Stoodley’s developmental neuroscience lab at American University is using this technique to modulate specific regions in the brain and examine how activity in whole-brain networks changes as a result. As a doctoral student in Dr. Stoodley’s lab, I have used neuromodulation techniques to transiently alter neuronal activity in the brain and measure changes in brain activity using fMRI. Combining brain modulation with brain imaging is a novel approach to investigating brain function. In particular, our lab uses transcranial direct current stimulation, or tDCS, a non-invasive neuromodulation technique, which involves running very low levels of electric current through the brain via an electrode placed on the scalp.
Our lab is interested in the effects of tDCS on the cerebellum—a part of the brain involved in both motor and cognitive aspects of behavior. When these two techniques (fMRI and tDCS) are combined, we are able to not only modulate brain activity, but also measure how brain activity changes as a result of modulation. We are one of the first labs in the world to combine these two methods to study the role of the cerebellum in cognition.
In one current study, we are examining the effects of tDCS to the cerebellum on the organization and connectivity of language networks in the brain. The cerebellum is especially important for predictive language processing—taking in language input and predicting what might come next. Being able to accurately form predictions and change behavior based on feedback is necessary for language-learning early in life and even carrying on conversations. It is thought that without the ability to predict “what comes next” when someone is speaking, language processing would be significantly slower and less efficient. In fact, damage to the cerebellum can result in language disturbances including mutism and trouble forming grammatical sentences. Increased cerebellar volumes have been related to better language skills and improved second- language learning abilities.
We have applied tDCS to areas of the cerebellum implicated in language. These regions of the cerebellum connect to other language areas in the brain, including those important for speech production, comprehension, and reading. Healthy young adults relaxed in the fMRI scanner while we collected resting-state fMRI data. Resting-state fMRI allows us to tap into what the brain looks like at rest, when no tasks are being performed. This gives us insight into the intrinsic activity of the brain and how regions in the brain work in concert to form networks. Based on patterns of correlated activity between multiple brain regions, we can measure the degree of connectivity between different regions of the brain. Abnormal patterns of connectivity in resting-state networks are implicated in a variety of disorders, including autism, Alzheimer’s disease, and drug addiction. In this study, we compared resting-state network connectivity in participants who received tDCS with those who did not receive tDCS. We found that neuromodulation of language areas in the cerebellum resulted in increased connectivity in a widespread network of language regions, suggesting enhanced communication between these areas. In particular, we found increased connectivity between language regions important for motor control of speech. These regions are important for producing the movements necessary to speak effectively, and are altered in patients with language disorders.
Techniques like tDCS are non-invasive, portable, and relatively inexpensive. Therefore, there is great interest in the potential use of tDCS to improve quality of life in clinical populations. Research into the effects of language network modulation could help people with disturbances of language, or aphasias, which can be caused by stroke or damage to language regions of the brain. Almost 250,000 new people each year in the United States suffer from aphasia, and in two-thirds of these cases, recovery is incomplete. Currently, treatment options are limited to speech therapy.
In fact, Dr. Stoodley and the developmental neuroscience lab have recently been awarded a National Institutes of Health grant to study the effects of cerebellar tDCS in aphasia. Our findings that tDCS can modulate language networks will inform future clinical applications of tDCS, and, hopefully in the future, a clinical trial of tDCS for aphasia.