The person who posted this question was directed to this blog and it is a very important question. After reflecting on it for a few days, I thought I would tackle it. The question itself is loaded with multiple layers of complexity. Do you mean measuring neuroplasticity in humans or in animal models of brain injury? Do you mean at the level of a neuron; groups of neurons, brain regions or the whole brain? Remember that my answer to this question describes the situation now as I understand it-not next month or next year, since the field is evolving and discovering at a rapid
pace. Neuroplasticity is measured mainly for experimental research and not in everyday medical practice. This will undoubtedly change soon.
Cellular or neuronal plasticity: So let’s start with the level of the cell or the neuron; this is cellular or neuronal plasticity. Today, we can only measure cellular plasticity in animals using slices of living brain tissue (in vitro) or by examining neurons on the brain’s surface through high powered microscopes (in vivo). Some examples include, measuring synaptic or neuronal current change in response to a stimulus, measuring levels of particular neurotransmitters or other molecules that would indicate cell activity or change (molecular plasticity), and visualizing changes in number or form of synapses (synaptic plasticity) or growth of dendritic branches (morphological plasticity).
Neural plasticity: Although terminology to describe different types of plasticity is ambiguous, I think of neural plasticity as changes in groups of neurons or sections of brain tissue. In animals, sections of brain tissue can be analysed for presence of proteins that would indicate more connectivity between neurons. This work is mainly done in animal models of brain injury but this research could be carried out in humans who have sustained a brain injury and have donated their brain to scientific research. There are a few brain banks in the world that could probably undertake this type of research.
Researchers are becoming interested in proteins called neurotrophins which act like brain fertilizers and support neurons during plasticity. These neurotrophins are manufactured in the body (for example in liver or muscle) and also by support cells in the brain. They circulate in the body so levels of these neurotrophins can not only be measured in sections of brain tissue but also in the blood and in the cerebrospinal fluid (the clear fluid that circulates around the brain and spinal cord). The fact that they can be measured by a blood test or lumbar puncture (spinal tap) may become important in humans over time. Really, these proteins are ‘markers’ of plasticity rather than measures of neuroplasticity itself. Certain markers in blood or cerebrospinal fluid may indicate plasticity going on in brain. This is still being worked out and no one knows what changes in blood or cerebrospinal fluid levels of neurotrophins really means. If you have higher levels does that mean there are higher levels in the brain? Perhaps lower levels are ‘better’ if it means that these neurotrophins leave the body’s general circulation and enter the brain.
Cortical Plasticity means plasticity of cortical maps on the surface of the brain. There are several methods to measure this. One of these is intracortical microstimulation (see post Focused skilled arm and hand training after brain injury promotes recovery and alters brain maps). This technique is performed in primate research in brain recovery. The other methods that I have discussed in the post ‘The tools to map your brain’ are being used in humans and probably have the most potential, in everyday practice in the future, to measure brain plasticity during recovery from brain injury.