Question: are there chemicals which could be used in medicine to stimulate certain parts of brain to replace parts of the certain parts of brain that are damaged. for example if one part of ther brain could be used to do a similar function as another part could this part could be stimulared through chemicals if one is unable to work correctly.

Carolyn McGettigan answered on 17 Mar 2010:

So far there hasn’t really been much success in stimulating growth of damaged neurons through treatment. One approach has been to try implanting stem cells into the brains of Parkinson’s patients, for example, to replace the dopamine-producing cells that die in the disease. However, an important point that has come up in the discussions this week is that repairing an injured brain is not just about putting the right cells back in, it’s also about making sure these survive and make the right connections with the intact cells in the brain, so that the neural pathways supporting cognitive function can be restored. What makes this extra difficult is that many types of brain injury are much less precise even that Parkinson’s, for example the damage sustained after stroke. This can kill not only the main cell bodies of neurons in one brain area (‘grey matter’), but also damage surrounding ‘white matter’, which includes the long tracts of the nerve cells that form the connections with other cells around the brain. When you consider that there are something like 100 billion neurons in the human brain, and that each can make thousands of connections with other neurons, that’s a big re-wiring job!

Aside from this kind of treatment, there are other ways in which function can recover after a brain injury. There is a lot of evidence for ‘functional re-organization’ after someone has a stroke, which probably involves more effective use of the bits of the brain and the connections that survive and can perform similar functions to those lost. There is also evidence for changes in brain structure with specific training – healthy people learning to juggle showed increases in grey and white matter after six weeks (although the cellular mechanisms for the changes are as yet unknown and may not involve the growth of new neurons). Although much, much trickier, some structural changes could hypothetically occur with targeted behavioural therapy after brain injury.

We also know that there are many drugs (e.g. Ritalin) which can act on the chemicals involved in communication between neurons, and these can lead to cognitive benefits in aspects of attentiveness, memory and control of behaviour in groups like patients with Alzheimer’s and children with ADHD. There is considerable controversy in the news about these being used illegally by many University students to improve their exam performance. Potentially, these are drugs that, when administered during a period of intense cognitive training (like revision for exams, or maybe even training after stroke) could trigger functional and structural changes in the brain. But again, these wouldn’t be able to achieve the specificity needed for full ‘repair’, and achieving an appropriate balance in all the chemical ‘neurotransmitters’ in the brain and how their various pathways interact is a very tricky business, so changing one would probably have effects on the others.

I’d suggest putting this question to Mariana too, as her research is on how neurotransmitters like glutamate are involved in neural learning.