Monday, June 23, 2008
Only a few decades ago, it was generally agreed that the lower brain and neocortical areas were immutable/unchangeable. In other words, the brain functions are fixed in certain areas:
Indeed, developmentally, it has been shown that the sensory pathways are fixed after a certain critical period. However, it has gradually become clear that the continued re-wiring of the brain, throughout life, largely influenced by the environment, is also operational. (A grand unification theory is needed here.)
Simplistically speaking, beyond the basic developmental plasticity, there are at least two other types of plasticity: one induced by injury repair and the other simply from learning and memory. In brain repair, the functions can move to different locations, and in learning/memory, specific brain areas can expand.
Neurologists have long observed that spontaneous recovery from brain lesions is common. For example, in an fMRI study (Pantano et al, Brain 125: 1607-1615, 2002), MS patients who had suffered a single attack of hemiparesis, there are adaptive changes involving both the symptomatic and asymptomatic hemispheres - during a simple motor task. And the extent of these changes increased with the lapsed time and the severity of damage .
There are simply too many such examples to cite, so we won't even attempt. Readers are encouraged to google their own.
And in this news article: "Taxi drivers' brains 'grow' on the job" (BBC News, 14 March, 2000): "...The hippocampus is at the front of the brain and was examined in Magnetic Resonance Imaging (MRI) scans on 16 London cabbies. The tests found the only area of the taxi drivers' brains that was different from the 50 other "control" subjects was the left and right hippocampus... One particular region of the hippocampus, the posterior or back, was bigger in the taxi drivers..."
These Knowledge Boys/Girls are special, aren't they.
Notice in the above, the research methodology was based on MRI yet again. In fact, both morphometric and functional MRI.
Let's not stray too far from the eye. If you recall "3.3.1 Who's being lazy" and "3.3.2 Squint", here is something extra that is relevant to brain plasticity:
"...The gray matter volume in strabismic adults was smaller than that in normal subjects at the areas consistent with the occipital eye field (OEF) and parietal eye field (PEF). However, greater gray matter volume was found in strabismic adults relative to normal controls at the areas consistent with the frontal eye field (FEF), the supplementary eye field (SEF), the prefrontal cortex (PFC), and subcortical regions such as the thalamus and the basal ganglia. These opposite gray matter changes in the visual and the oculomotor processing areas are compatible with a hypothesis of plasticity in the oculomotor regions to compensate for the cortical deficits in the visual processing areas..." (See Chan et al, Neuroimage 22:986-94, 2004.)
The next step is confirmation with fMRI. Time to write a grant application, then.
Maybe an introductory paragraph starting with:
"Visual deficits can be correlated to less gray matter at the striate and extra-striate visual cortex. In particular, visual motion deficits can be correlated to less gray matter at the parietal eye field, and normal saccade responses can be correlated to more gray matter at the rest of the oculomotor regions..."
Then again, maybe not.
Posted by EyeDoc at 11:29 AM