In the quest to unravel the way the brain works (any brain, we can learn a lot from a mouse brain that applies to our own brain) researchers are looking for better and better ways to detect electrical signals exchanged by neurones. Indeed, the electrical activity is crucial to brain data processing. We know a lot on the way a single neurone processes an electrical stimulus and how this leads the neurones to generate other electrical stimuli towards many neurones it reaches through synaptic contacts.
We also know that neurones are organised in circuits, similarly to the way transistors are organised in circuits in a chip to perform a specific function. The problem with neural circuits is that it is much more difficult to isolate and therefore identify them. There are so many connections, in the order of a thousands per neurone (Purkinje neurones, found in the cerebellum, have up to hundred thousands synapses), that it gets mind boggling to follow the connections of a few hundreds neurones, such as those that may form a neuronal circuits (in case of transistors we may say that a hundred transistors forming a circuit do so through a hundred connections!).
It is even more complicated! Neurones that are connected not necessarily are part of the same functional circuit (unlike transistors). Hence, the map created by the Connectome project does not help in the identification of neuronal circuits (mind you: in order to be part of a neural circuit two neurones need to be connected one another or through a chain of other neurones, but two neurones that are connected are not necessarily involved in the processing of a signal – carry out a function).
In order to detect neuronal circuits you need to detect which neurones “fire” in response to a signal (a stimulus). And this requires detecting their electrical activity. The problem is finding a way to detect such activity with a good precision identifying the neurones involved.
Current probes (electrodes) can capture an electrical activity but the cannot pinpoint the source and it is not possibile to capture the activity of hundreds of neurones in parallel separating the activity of one from the other.
This is the issue that has been addressed by neuroscientists at the Francis Crick Institute by creating a nano probe called nanoengineered electroporation micro-electrodes, NEMs for short. You can see its shape in the picture. The tip of the probe is about 5µm thick and 30 µm in length. It accommodates some 20 “pores” detecting electromagnetic field. By analysing the different values of the field detected in the different pores the neuroscientists have been able to map the activity of the neural circuits processing olfactory stimuli in a mouse brain. That circuit consists of about 250 neurones that are contained in a space of 50µm, about the length of the probe tip.
The next decade has been labelled “the decade of the brain”: the availability of new technologies, like this one, will help in the understanding the brain’s work at neuronal circuits level, a first step towards understanding the brain working as a whole.