Research into possible treatments for brain injury has often focused on the area of neural plasticity. Plasticity is the property of neurons in the brain to reorganise themselves and form new connections, which is the mechanism by which learning and memory work. It has previously been well documented that such reorganisation takes place in the sensory and motor areas of the brain and new evidence shows that it may also take place in the visual system.
Previous studies of adult visual system plasticity have provided mixed results and the evidence has been far from clear. However, neuroscientists from MIT and Johns Hopkins University have found evidence from a stroke patient that reorganisation does occur, and that the changes affect visual perception. The study, published in the September 5th issue of the Journal of Neuroscience, examined behavioural and neuroimaging evidence from a patient known as B.L.
B.L suffered a stroke which caused damage to the area of his brain that processes information from his upper left visual field (LVF). As a result, the area of the visual cortex that normally receives information from this area was left deprived of input. As expected from the damage, B.L is blind in the upper LVF. However, surprisingly, he reports distortion in the lower LVF. The scientists hypothesised that the distortion was a consequence of reorganisation of the primary visual cortex.
The researchers tested B.L by presenting shapes, such as a square, to his left visual field while he fixed his gaze on a centre dot. As expected he was blind to objects in the upper LVF, but as the shape was moved just below the blind field he perceived an elongated rectangle rather than a square. The elongation projected towards and into the upper blind field. Likewise, he perceived triangles as "pencil-like" and circles as "cigar-like". The scientists hypothesised that the distortion was a result of reorganisation of the primary visual cortex and this was supported by functional magnetic resonance imaging (fMRI). As the authors state, "these findings contribute to our understanding of the human adult brain's capacity to change and has implications for topics ranging from learning to recovery from brain damage."
Reference: Dilks et al., 2007, Human Adult Cortical Reorganisation and Consequent Visual Distortion, Journal of Neuroscience, September 5th, 2007, 27(36): 9585-9594
Back