October 4, 2007
UNIT 9: Human BiologyAdult Brains Can Rewire after a Stroke
A child’s brain has an amazing ability to adapt and change to new experiences — it is very plastic. Over the past 25 years, researchers have found that an adult’s brain also has plasticity. Many times, its plasticity helps an adult master a new skill or adapt to a changing environment. Sometimes, the plasticity makes up for an injury.
A case study of a stroke patient adds to evidence proving that adult brains are capable of creating new neural pathways. The victim, known as BL, had a stroke that left him with a blind area in his upper left visual field. BL described how objects “looked distorted” in the lower left visual field, right below his blind area. Neuroscientists from Johns Hopkins University and Massachusetts Institute of Technology hypothesized that these distortions were caused by rewiring in the visual cortex, the part of the brain that processes visual information, to compensate for the stroke.
Dr. Daniel Dilks of MIT, and his collegues tested their hypothesis. BL was shown basic shapes while he stared at another object. When they presented the shapes in his upper left visual field, he recorded seeing nothing. But when they presented the shapes just below his blind area, he recorded something different. Triangles appeared pencil-like. Circles appeared cigar-like. Squares appeared like rectangles. The shapes extended up into his blind area. His brain had rewired to use the part of the visual cortex that no longer received direct visual information.
The fMRI studies confirmed that the deprived visual cortex began to assume new properties that led to the visual distortions. “We discovered that it (the visual cortex) takes on new functional properties, and BL (the stroke victim) sees differently as a consequence of that cortical reorganization,” Dr. Daniel Dilks says.