This post is also available in Dutch.
In the past few blogs, you were able to read about how we measure ongoing brain activity. But, we can also induce brain activity or disrupt it. We do this by manipulating generated electrical currents to create communication between neurons, also called action potentials. By carefully monitoring these manipulations, we can discover their effect on behavior. For instance, we can discover which areas are relevant for certain cognitive tasks.
There are actually many different methods for manipulating the brain. Amongst others, there are transcranial magnetic stimulation (TMS), transcranial electrical stimulation (TES) and transcranial ultrasound stimulation (TUS). The effect of these methods is quite similar but how they work is different.
Electrical currents, magnetic fields or ultrasound?
With each of these methods, we use special equipment enabling us to manipulate the electrical currents generated by the neurons. With TES, we use electrical currents as well, while with TMS, we use magnetic waves to activate or disrupt brain activity. With TUS, we use ultrasound, which means sound waves at a frequency so high that we can’t hear it. Yes, the same thing is used to make images of a fetus in the womb. But in that case, no nerve cells are impacted; only ‘echo’ images are made. However, if we really focus those ultrasound waves to one specific point, the energy will increase at that point, like the sun through a magnifying glass. This is the type of ultrasound we use for brain stimulation at the Donders Institute.
Each of these methods can, depending on the research question at hand, stimulate or disrupt activity in a specific area in its own, unique way.
Decreasing Depression with TMS
These methods are not only used to research communication between brain areas, but also to impact brain activity in a sustainable manner to treat mental diseases. For example, a special type of TMS consists of a range of short magnetic pulses. This type of TMS can be used to stimulate dysregulated areas of the brain, for instance, in people with depression. By stimulating the brain, symptoms of depression can actually decrease.
Not that simple and not as easy as it seems
Now this seems like a clear-cut story: we stimulate neuron ‘A’, we see a change in brain area ‘B’ and this leads to behavior ‘C’. That’s a wrap, right? Unfortunately, it’s not that simple. The brain consists of a huge number of neurons with tangled connections that are constantly communicating. Compare it to a junction where half of New York City is trying to cross. Pure chaos. This makes it particularly hard to stimulate just one connection and also not affect other areas in the brain. It should therefore be noted that ‘A’ does not necessarily lead to ‘B’, and that other factors are also at play. For instance, someone’s emotional state: the brain of a sad person can respond differently to stimulation than that of a happy person. We should be careful to keep this in mind when applying these methods in research.
Would you like to experience brain stimulation? You can participate in research at the Donders Institute via SONA!