Seeing brain plasticity in the environment

Photo credit: Emma Goodman 

You are where you live. If you open your eyes wide enough, you'd see that your environment really is the most important thing in your life.

A paper published this week in the Journal of Neuroscience suggests that the ability of the adult brain to re-wire itself depends on the quality of the environmental stimulus. What's more, perhaps this can occur more quickly than previously thought. [Matthies U et al. J. Neurosci. 2013;33:11774-11778].

Our brains are plastic organs that are capable of moulding and re-wiring themselves in response to the changing environment. The visual cortex is a great example of this 'brain plasticity'. Young children deprived of vision to eye one during a certain critical period of their growth often develop 'lazy eye', or amblyopia. This occurs because without anything to 'look at', the brain region responsible for vision in this eye does not develop properly. Young children's brains are incredibly adaptable, and this problem can be easily fixed just by correcting the eye problem. Of course, we've all heard that old dogs can't learn new tricks. Unfortunately, after a certain age in childhood, the brain not longer has the capacity to re-wire itself and fix the problem, making untreated lazy eye a problem for the rest of adult life.

However, scientists are now learning that adult brains are far more plastic that we traditionally gave them credit for. We now know that it is possible to encourage this 'plasticity', or brain re-wiring, in the adult animal, even after this critical period has ended. So hopefully one day we will have effective treatments for lazy eye, or any other disorders that the brain could fix itself if it just new how.

This study wanted to find ways to enhance this adult brain plasticity. To do this, the researchers needed to induce the visual cortex to undergo plasticity in the first place. To do this, they covered one eye of adult rats for 4 days so that not visual stimulation reached this eye (similar to what happens with lazy eye).

How did they know if the brain re-wired itself? Thankfully, neuroscientists have access to some great modern imaging technologies. Using our understanding of how light interacts with brain tissue, we can 'look inside' a living brain. Here's a great lecture that explains these technologies and what we can use them for, if you have an hour spare to devote to your own brain plasticity:

Figure 2: 'Ocular Dominance Index' (ODI) changes from day 2 onwards, indicating plasticity is taking place at this time.

These researchers used 'optical imaging' to measure brain activity. They saw more activity in  the brain region responsible for the open eye compared to the closed eye, indicating that plasticity was taking place and the brain had re-wired itself in favour of the open eye. What's more, this occurred after just two days. So, ta-dah! Don't give up on your noggin just yet. Here's an example of how old rats can learn new tricks!

But whilst adult brain plasticity does occur, it needs a little bit of assistance... In this case, the researchers were testing whether a particular type of visual stimulus could induce adult plasticity. During their monocular deprivation, the rats were placed in a box with special mirrors so that all they could see was an organised, repeatedly-moving stimulus. The idea was to test whether the timing of the stimulus is what allowed the brain to re-wire itself.

So does your environment really matter? Yes it does! Adult rats that were exposed to a grey background or randomly moving circles, instead of these moving square gratings did not show the same amount of brain plasticity. So compared to the random firing of neurons that comes from the deprived eye, using this type of organised visual stimulus produces a much clearer signal that clearly tells the brain it should re-wire in favour of the open eye.

This study suggests that the mechanisms that allow the adult brain to re-wire itself are perhaps not so different from those of young brains... All you need it the right environment.