Wednesday, 7 January 2015

Is it possible to record from single neurons with EEG?

Electroencephalography, or EEG, is a technique that has allowed scientists to take recordings of activity of large populations of neurons (the cells of the brain that communicate with each other electrically). EEG has furthered our understanding of sleep, enables us to make accurate diagnoses of conditions such as epilepsy, has given us a glimpse into how higher cognitive processes work and has provides the basis for brain-computer interfaces. 

It allows us to glimpse into the inner workings of the human mind without having to perform dangerous surgery, even babies are happy to have their brains recorded from with this equipment. However, whilst EEG is great at the moment for looking at the activity across large amounts of neurons (thousands to millions in fact) at an incredible time resolution. There is as yet no way of recording from single neurons in such a non-invasive way. Doing so might help us to uncover unimaginable amounts of new information about the workings of the human brain.

Even babies are happy to have their brains recorded from.

A recent study has aimed at making it possible to calculate the contribution of a single electric signal (or action potential) from a single neurone to the overall EEG signal. Essentially they averaged out a number of simultaneous EEG recordings of a specific region of macaque brains called the somatosensory cortex (where the brain processes the location of sensations) and correlated them with individual cell recordings. What they found was that for certain neurones there is a correlation with certain frequencies of EEG, however there are a number of confounding variables that make it difficult to be certain at this time. These variables include the type and size of neurones, their location, the amount of activity in neighbouring neurones and many more, which results in a vast amount of noise that is often greater than the contributions from the neurones in question. 

While this is a promising first step in being able to record from single cells non-invasively, it is important to note that we are far from being able to do this in real-time and that the authors are very careful not to overstate their claims.  These recordings were made in ideal conditions for this kind of experiment over thousands of repeats and then the data was analyzed afterwards to look for contributions from single neurones, however the findings here do agree with the predicted contributions calculated by simulations. Ultimately this and further studies may help to narrow the gap between the macroscopic recordings of EEG and microscopic recordings from single cells. 

If you want to read the paper there's a link to the manuscript here.
If you want to learn a little bit more about how EEG works you might find this video useful. 

Source:Bartosz Telenczuk, Stuart Bakerd, Richard Kempterc, Gabriel Curio. Correlates of a single cortical action potential in the
epidural EEG. Neuroimage; In press 2014 doi:10.1016/j.neuroimage.2014.12.057.


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