After a stroke, the brain suffers more broadly than just at the spot that was starved of blood. New research, which uses brain imaging to examine connections between different parts of the brain, shows that communication between the left and right hemispheres is often disrupted; the greater the disruption, the more profound the patient’s impairment in movement or vision. Researchers hope to use the approach to predict which patients are mostly likely to recover on their own and which will need the most intensive therapy.
The study is part of a broader effort to incorporate the brain mapping technology into post-stroke assessment, including new clinical trials testing experimental drugs and physical therapy in combination with imaging. Mapping brain connectivity and recovery may give scientists a better measure of which treatments most effectively enhance the brain’s innate plasticity–its ability to rewire–and when the brain is best primed for repair.
“The kind of information we’re getting from neural imaging studies is giving us a better understanding of the kind of changes that are important during recovery,” says Alexandre Carter, a neurologist at Washington University, in St. Louis, who led the study.
Stroke patients typically undergo an MRI to identify the precise location of their stroke. But these brain scans don’t show how the damaged part of the brain fits into the larger network–the neural connections that feed into and out of this spot. Just as a delay at one station of a subway system can affect service at numerous stops and subway lines, dysfunction in a localized part of the brain disrupts activity in several different parts.
In the new study, researchers assessed this disruption by creating a functional connectivity map of the brain in people who had recently suffered a stroke. They asked patients to lie quietly in an MRI machine and used functional MRI, an indirect measure of neural activity, to detect spontaneous fluctuations in brain activity. Brain areas that are well-connected will fluctuate in synchrony, providing an indirect way of mapping the brain’s networks.
As is often the case with stroke, they found that patients’ visual or motor problems were limited to just one side of the body, such as a weak left hand or an inability to pay attention to objects in the left side of the field of vision. (Because the left side of the brain typically controls the right side of the body and vice versa, a stroke on one side of the brain will affect the opposite side of the body.) But the researchers found that patients with these symptoms had disruptions in the connections between the two hemispheres. And the level of disruption between the two halves of the brain correlated to the severity of their impairment. “The physical damage has repercussions all throughout the network, like a ripple effect, even in areas that aren’t physically damaged,” says Carter.
The research, published this month in the Annals of Neurology, is the first step in a multiyear project assessing how to predict how well people will recover from stroke. Researchers will repeat the brain scanning and behavioral testing months after the patients’ strokes to see how both change over time.
Carter and others ultimately aim to use the technology to better target stroke treatments. “It’s important to know what lies behind recovery, because we want to have a brain-based understanding of new treatments,” says James Rowe, a neuroscientist at Cambridge University, in the U.K., who was not involved in the study. In addition, he says, because this kind of scan can be done very early, “we might be able to classify patients who would benefit from one type of therapy or another.”
Two patients who have similar motor impairments might actually have very different disruptions to their brain networks and therefore benefit from different types of treatment. For example, not everyone responds to constraint-induced movement therapy, in which the strong arm is bound, forcing the patient to use their weak arm. Analysis of network dysfunction might help predict which patients will benefit from this treatment.
The research is part of a broader effort to capitalize on the inherent neural plasticity that is present even in the adult brain. “There is more and more interest in changes in the brain that occur at more chronic stages of stroke,” says Rick Dijkhuizen, a neurobiologist at University Medical Center Utrecht, in the Netherlands, who was not involved in the current work. “Increasing evidence suggests that the brain is able to reorganize even in patients [whose strokes occurred a long time ago], and this gives us opportunities to look at stroke therapies to promote this organization.”