The human brain represents arguably the most complex and fascinating organ of our body: hidden inside our head, it controls most of our activities and processes all the information gathered from the outside, pulling it all together to interpret the world around us. Our brain is responsible for our thoughts and our culture; our feelings and our passions; for me writing these words and for you reading them: simply put, the brain is what creates our personality and our consciousness. 

 

It has been almost 700 years since we have started studying the brain. Today, our understanding has come a long way and we now know that the neuron is the functional unity of this organ. The brain contains around 86 billions of these special cells, densely interconnected with each other, exchanging signals and information in the form of electrical pulses. Measuring these signals is not easy; nevertheless, scientists are developing increasingly precise instruments to measure the electrical activity of the brain, which are playing a huge role in revealing its physiological mechanisms. 

 

To do so, today we use the so-called “neuroelectronical interfaces”, that is, tools that establish communication between the brain and external devices, measuring and recording brain activity. Doing this while a task is being performed (such as watching an image, walking, or eating), can give us a useful insight into which areas of the brain are involved in the control of said task. Many instruments of this sort have been developed, and each one of them has a trade-off to face: invasiveness or spatial resolution. Tools that record brain activity from the outside are completely safe and quite bearable for the subject that is asked to wear them, but they can only record the activity of whole areas of the brain. On the other hand, tools that are implanted inside the brain are potentially more dangerous and difficult to tolerate, with the risk of bleeding and infection, but they are precise enough to measure the activity of a single neuron, allowing us to investigate the involvement of individual cells in a process. 

A research group led by Anqi Zhang, in a collaboration between the universities of Stanford and Harvard, has recently developed a device that aims to overcome this trade-off: they designed an instrument that could be temporarily inserted into the vasculature of the brain, without the need for permanent implant or any excessively invasive surgery. Why measuring brain activity from inside the blood vessels? The big advantage of this approach is the spatial resolution potential. 

 

The brain needs a lot of energy, which is delivered by a very dense network of capillaries that reach the proximity of virtually every neuron. Therefore, the blood vessels in the brain give access to any area of the brain we might be interested in. However, these blood vessels get smaller the deeper they go into the brain, posing a considerable challenge for the dimensions of these devices. 
 

This is not the first time that brain activity has been recorded from inside its vasculature. However, the tools used so far were relatively large, and they could be inserted only in the largest, most superficial blood vessels, giving access to a limited number of brain areas. Zhang and his team managed instead to build a probe that is so small and flexible that it can be inserted into vessels smaller than 100 micrometers (that is, less than a tenth of a millimeter, similar to the thickness of a single hair!). This tool, called the MEV probe, bears many microscopic metal electrodes, that are pushed to the vessel wall and measure electrical signals coming from the adjacent neurons. Working with rats, they inserted small catheters into the blood vessels of the neck and used them to inject the probe into two different areas of the brain: the cortex and the olfactory bulb. After confirming its correct placement, they managed to record the activity of these areas with great spatial and temporal precision, measuring single electrical pulses from individual neurons. Finally, they evaluated the inflammatory response induced by the probe and found no indication of brain inflammation, neither immediately after implantation nor after 28 days. 

These impressive achievements represent a significant technological advancement for the neurosciences. Understanding how the brain works is extremely challenging, and the technological limitations are still a big hurdle to be overcome in this field. However, new instruments such as the MEV probe are a great chance to learn more about our brain, opening the door to a better detection of neurological diseases and more accurate medical intervention.