Virtual Lesions in the Language Network: Exploring Brain Plasticity After a Stroke

Anna Brinks 21′

Figure 1. Diagram of a hemorrhagic stroke, which is caused by a blood vessel bursting and bleeding with the brain (Source: Wikimedia Commons).

Strokes effect an overwhelming number of people: in the United States, someone has a stroke every 40 seconds and 1 in 20 deaths are the result of stroke.1,4 A stroke can occur when blood supply to part of the brain is blocked (ischemic stroke) or when a blood vessel in the brain bursts (hemorrhagic stroke.) This can cause brain tissue to become damaged or die, potentially resulting in lasting disability or death. Unfortunately, having one stroke increases the risk of a second: up to 15% of those who have suffered a stroke will have another stroke.3

However, promising research has shown the brain is far more malleable than previously thought.3 After a stroke, neighboring regions of tissue surrounding the damaged area and sister areas on the other side of the brain are activated. Using virtual lesions simulated by electrical stimulation, researchers at the Max Planck Institute for Human Cognitive and Brain Sciences explored whether activation of the right hemisphere is adaptive for language recovery after a second stroke.2 Scientists studied 12 patients who sustained previous injuries in regions of the brain responsible for processing sound. The researchers simulated a second disruption using transcranial magnetic stimulation (which uses electrical current to temporarily inhibit brain function) and then tested the participants with a simple decision task where participants were asked if the word “cat” consisted of one or two syllables.3

The researchers found that individual impairment predicted activation on the right side of the brain, and that patients with stronger fiber connections between sister areas on the right hemisphere were less affected by the disruption.3 This indicates that the right hemisphere likely plays a beneficial role in compensating for large-scale disturbances that inhibit the functioning of the left hemisphere. However, if the right hemisphere remains permanently upregulated due to damage sustained by the stroke, this could prevent the left hemisphere from properly healing.3

The large-scale networks in the brain that allow language processing are highly complex and can be severely impacted by strokes. This study has important implications for the future of stroke treatment and the improvement of language recovery in affected patients by providing insight into new therapy options. Noninvasive therapy involving upregulation or downregulation of key brain regions via transcranial magnetic stimulation could increase brain plasticity and allow for faster stroke recovery.

References:

[1] Benjamin, E. J., Blaha, M. J., Chiuve, S. E., Cushman, M., Das, S. R., Deo, R., de Ferranti, S. D., Floyd, J., Fornage, M., Gillespie, C., Isasi, C. R., Jiménez, M. C., Jordan, L. C., Judd, S. E., Lackland, D., Lichtman, J. H., Lisabeth, L., Liu, S., Longenecker, C. T., … Muntner, P. (2017). Heart Disease and Stroke Statistics—2017 Update: A Report From the American Heart Association. Circulation135(10). https://doi.org/10.1161/CIR.0000000000000485

[2] Hartwigsen, G., Stockert, A., Charpentier, L., Wawrzyniak, M., Klingbeil, J., Wrede, K., Obrig, H., & Saur, D. (2020). Short-term modulation of the lesioned language network. ELife 9, e54277. https://doi.org/10.7554/eLife.54277

[3] Max Planck Institute for Human Cognitive and Brain Sciences. (2020, March 23). Stroke: When the system fails for the second time. ScienceDaily. Retrieved March 24, 2020 from www.sciencedaily.com/releases/2020/03/200323135251.htm

[4] Yang Q. et al. (2017, September 8). Vital Signs: Recent trends in stroke death rates – United States, 2000-2015. CDC, MMWR 66(35), 933-939. http://dx.doi.org/10.15585/mmwr.mm6635e1

 

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