Dr. Argye Hillis, a Johns Hopkins neurologist, is an expert in aphasia and is currently focusing her research on improving aphasia recovery in stroke patients. Aphasia is the loss of ability to understand or express speech caused by brain damage, and in Hillis’ experience this brain damage arises from blood flow being cut off from language-oriented areas of the brain during stroke. When patients experience strokes, the lack of blood flow deprives brain cells of the oxygen and glucose they need to survive. Aphasia is specifically caused by strokes in the left hemisphere of the brain.
Hillis’ earlier research aimed to study the relationships between the structure and function of the brain by pairing MRI imaging with language tasks in stroke patients. Subjects were patients who had suffered left hemisphere strokes within the past year. Focus was specifically on the left temporal cortex and left posterior frontal cortex, which are the brain regions associated with language comprehension and articulation of speech. Hillis’s research identified correlations between changes in patients’ language ability with changes in the brain’s blood flow. Her studies concluded that in addition to speech-therapy, further improvement of language abilities could be brought on by restoration of blood flow to damaged brain parts and reorganization of neural connectivity.
Hillis and her colleagues at Johns Hopkins have recently joined efforts with researchers at the University of South Carolina and the University of California, Irvine to develop new ways to combat aphasia and help stroke patients achieve stronger recoveries. Their conjoined effort, which are being implemented in each of the three locations, is named the Center for the Study of Aphasia Recovery (C-STAR), and is being funded by an $11.1 million 5-year grant from the National Institutes of Health. Hillis is assigned as the principal investigator for C-STAR’s clinical efforts, and she is currently leading a study at Johns Hopkins to investigate the use of transcranial direct-current stimulation to augment language therapy.
Transcranial direct-current stimulation (TDCS) is a noninvasive form of neurostimulation that causes the resting membrane potential of neurons to depolarize when emitting positive stimulation or hyperpolarize when emitting negative stimulation. The stimulation is transmitted as a constant, low current through electrodes placed on the scalp and has been found to achieve cortical changes even after the direct stimulation has ceased. TDSC is traditionally used for treating depression, but Hillis believes it may benefit stroke patients’ ability to regain language skills when paired with language therapy. Her theory is that repeated exposure to TDSC currents will change the threshold of activation of the neurons used to perform language tasks, meaning less stimulation of the neurons will be required to reach action potential and transmit information. Hillis hopes that overtime, lower threshold of activation will lead to neuroplasticity, which is the ability of the brain to form and reorganize connections. Ideally, these new connections will result in new neurons taking the place of ones damaged during stroke, permitting a complete restoration of language abilities.
Another focus of the study is to observe and assess the interaction of TDSC and language therapy with selective serotonin inhibitors (SSRIs). On a cellular level, SSRI’s target serotonin transporters and prevent reuptake. This leads to an increase in serotonin in the synaptic clefts of neurons and promotes increased activity of the neurotransmitter in postsynaptic cells. SSRIs have been used in the treatment of stroke as a prescription and have been found to significantly affect the brain’s ability to overcome neurological deficit, though the exact mechanism performed to do so is unknown. Hillis aims to determine if there is an increased ability for patients to recover from aphasia when SSRI’s are paired with TDSC and language therapy, and she seeks to further understand why SSRI’s have beneficial effects.
Hillis’ study involves aphasia patients who have suffered from stroke within the past three months, and it is based on comparative data collection from a control group receiving conventional language therapy and an experimental group receiving TDSC paired with language therapy. Hillis used to be a speech-language pathologist and has prior exposure to language therapy. She believes TDSC will make a difference in patients’ ability to overcome language problems because her past experiences with language therapy have shown only limited effectiveness. Hillis’ ultimate goal is to find an improvement for aphasia recovery that will allow stroke patients to communicate effectively once again. Her study, in conjunction with other C-STAR efforts, will continue to strive towards developing better ways to treat aphasia and ultimately improve the quality of life for patients.