Finding a Voice After Stroke
Peter Turkeltaub, M.D., Ph.D., is clearly delighted and surprised by one of his recent studies on how the brain processes language.
When Turkeltaub asked a group of study participants to press a button indicating they could hear particular sounds hidden in background noise in their headphones, he found the acuity of their perception depended on which hand they were asked to use. In other words, what the subjects heard depended on what their hands were doing or about to do.
The study, presented in early October at the annual meeting of the Society for Neuroscience, revealed a previously unrecognized tight coupling between motor systems and perception, says Turkeltaub, a neurologist in the Center for Brain Plasticity and Recovery. “It’s pretty amazing. Imagine you are waving an American flag while listening to one of the presidential candidates. The speech will actually sound slightly different depending on whether the flag is in your left hand or your right hand,” he says.
The finding is just one more clue to the puzzle Turkeltaub is tying to solve: how does the brain process language? The answer will help him in his bigger mission: how do you help people who have lost speech regain it — such as those suffering aphasia after a stroke or who have experienced other brain injuries or even developmental dysfunctions?
“We want to understand the brain basis of language so that we can design more intelligent treatments for language problems when something goes wrong,” he says.
Turkeltaub is well on his way to meeting these goals. He is a lead researcher in the newly created brain center, a joint program of Georgetown University and MedStar National Rehabilitation Network, whose mission is to restore and expand neuroplasticity to help adults recover from a wide-ranging assortment of brain ailments. For GUMC, the Center capstones its strength in neurology and neuroscience, both in basic and clinical research.
He was also recently named recipient of a highly competitive and prestigious grant — a $486,000 award from the Doris Duke Charitable Foundation — intended to support junior physician-scientists as they transition to independence as clinical researchers.
In fact, Turkeltaub seeks to be one of the rare researchers in the new field of cognitive neuroscience who are focused on taking what they learn in the lab to the clinic to improve treatment of a neurological deficit. Cognitive neuroscience focuses on understanding how nerve cells interact with each other to produce thoughts and feelings and language — a systems approach to brain science. Most bench to bedside medicine looks at biology at the level of genes and proteins, which can lead to drugs that tweak this molecule or that. To make a difference in brain processes that control language, entire brain areas — specific gardens of neurons — need to be nourished or inhibited in novel ways.
Directing stroke recovery with tiny electrical charges
Investigations of brain areas involved in language suggest that the left and the right hemispheres contribute in different ways, and how these areas try to rebound after a stroke also varies. The left hemisphere appears to be the dominant region in language processing, although each area performs separate tasks.
The study Turkeltaub presented at the Society for Neuroscience was aimed at testing the prevailing theory that the left hemisphere prefers to process rapidly changing sounds, such as consonants, while the right hemisphere likes slowly changing sounds, such as syllables or intonation. The participants pressed their button when they could hear those sounds in headphones, but switched hands as the tests proceeded. “We were examining how the two hemispheres differed in the auditory processing — and we saw that — but we also just wanted to see if changing hands made a difference,” he says. The right hand is linked to the left brain, and vice versa, but no one had thought hand movements controlled language processing. It was a Eureka moment when the researchers found that hand activity mattered.
Turkeltaub also knows that most strokes causing language problems occur in the left hemisphere, and that to help repair the damage, the rest of the brain starts to take over some of the function that is lost. That works just fine when the left brain regions surrounding the injured area take over — but all too often, the right brain also tries to help out. A number of studies suggest that the right hemisphere doesn’t do as good a job in compensating for a stroke in the left hemisphere, and in fact, might make recovery worse, he says. “In kids, the right brain can take over language functions without any problem, but in adults, the right brain apparently can no longer handle language in the same way that the left hemisphere can, and so it might limit recovery when the right hemisphere becomes too involved,” Turkeltaub says.
To help guide the right kind of neural recovery, Turkeltaub is set to start a clinical trial by the end of the year to see whether a device worn on the head can improve language ability in people with post-stroke aphasia.
This device, called transcranial direct current stimulation (tDCS) is a portable, low cost, and safe to use device, that applies a very low level of electrical current — the equivalent of a nine-volt battery — to the brain. It increases the chances that neurons will fire or be inhibited, depending on where the charge is placed. “It is a mild way to enhance or inhibit functioning of particular parts of the brain,” Turkeltaub says. In fact, tDCS is being investigated for a number of different brain disorders, including depression, pain, even ringing in the ears. Two other labs are studying tDCS in aphasia, but Turkeltaub’s is the largest study to date, and the only one to test whether inhibition of the right hemisphere and enhancement of the left hemisphere improves language reacquisition.
It will represent a baby step forward, he believes, but one that is sorely needed for the million folks that have aphasia in America today. “So many people’s lives are changed dramatically after a stroke — they can’t hold the same jobs they did, they can’t speak to their loved ones as they once could — and we just don’t have good enough ways of helping these people right now,” Turkeltaub says. “It won't be a magic bullet, but if it can make even a little bit of difference, it might translate into a big improvement in a stroke patient’s life,” Turkeltaub says. “It provides a chance, and a hope, of getting better.”
By Renee Twombly, GUMC Communications