A New Method for Assessing Stroke Recovery
Post by Anastasia Sares
What's the science?
Stroke is a serious brain injury caused by the blockage or bursting of blood vessels that normally carry oxygen to the brain. This leads to the death of some neurons, which affects the ability of the brain to function. For example, many stroke patients have movement and speech-related difficulties. However, the brain does have the ability to “bounce back” somewhat from a stroke, reconfiguring itself so that lost functions are regained. Doctors aren’t able to fully predict how much an individual will recover, as recovery depends on a number of factors. This week in Brain, Tscherpel and colleagues demonstrate how a combination of transcranial magnetic stimulation (TMS) and electroencephalography (EEG) can be used to reveal a patient’s potential for motor recovery.
How did they do it?
Transcranial magnetic stimulation, or TMS, involves stimulating the brain by using quick magnetic pulses applied to the scalp. The magnetic pulse interferes with the electrical signaling of the neurons, causing some neurons to fire while inhibiting others. Electroencephalography, or EEG, is a technique to measure the electrical signals coming from the brain. By combining TMS and EEG, we can deliver magnetic pulses to a brain area (the motor cortex, in this case) and also measure how the brain responds to that stimulation. The authors used this technique on a group of stroke patients with different levels of severity and compared them with healthy volunteers of the same age range. They evaluated them within the first two weeks of their stroke and followed up about 3 months afterward in order to track their recovery.
What did they find?
The healthy volunteers with no stroke showed “a sequence of positive and negative deflections” in response to the TMS stimulation, much like ripples. In contrast, some of the stroke patients showed fewer ripples, with the most extreme cases having only one single larger peak of activity. Features of the electrical response were correlated with the patients’ severity at the first visit and also with recovery at the next visit (note that recovery did not depend on the initial severity of the stroke). By looking at the patients’ brain structure, the authors also determined that these abnormalities in the electrical response were related to deep brain structures and white matter, not the neurons in the motor cortex. This indicates that recovery may depend on white matter connections between different regions.
What's the impact?
Doctors have existing tools that can measure the severity of a stroke (motor-evoked potentials, for example), and predict recovery to some extent. However, these tools cannot fully predict recovery, especially for those with severe strokes. TMS and EEG are less expensive than other brain imaging techniques like MRI or PET, so this technique warrants further investigation for tracking stroke recovery in a clinical setting.
Tscherpel et al. Brain responsivity provides an individual readout for motor recovery after stroke. Brain (2020). Access the original scientific publication here.