Picking up the brain’s electrical signals Electroencephalography is a well-established technique for investigating the function of the human brain and certain neurological conditions, yet conventional methods have some significant shortcomings. We spoke to Professor Silvia Comani, PhD about the ANDREA project’s work in developing a novel dry electrode system A technique designed to record electrical activity in the human brain, electroencephalography (EEG) enables scientists to gain new insights into its function. The standard approach with EEG is to use socalled ‘wet’ electrodes, so named because a conductive material like a paste or gel is required to enhance the quality of the recorded signal and to reduce the impedance between the sensor and the surface of the head, yet this procedure has a number of drawbacks. “Firstly, this is a time-consuming procedure, especially when high-density recordings are required. For each electrode, you need to apply the paste, to adjust the impedance and to achieve the best possible contact between the head and the sensor. This takes on average a minute per electrode,” explains Professor Silvia Comani, the Principal Investigator of the ANDREA project. A second major disadvantage of traditional ‘wet’ electrode systems is that the preparation of the skin during the application of the gel may induce allergies in the subject and errors in the recording. “This gel may leak, and that may lead to cross-bridges between adjacent electrodes, hence to a contamination of the recording,” outlines Professor Comani. Prototype cap with 97 dry Multipin electrodes (cap turned inside out).
Andrea project The ANDREA project aims to develop a novel, dry electrode system which will overcome these issues. There are already some systems which use dry electrodes, yet in many cases they are quite painful for the subject to actually wear; Professor Comani says researchers in the project have developed innovative, flexible polymer electrodes that can be used with relative ease. “We’ve been developing electrodes in a specific shape, so that they can be kept on the subject’s head for up to an hour with no real problems, no pain,” she explains. These electrodes are integrated into a cap network, which can be adjusted to fit the contours of an individual subject’s head. “The cap is cut to fit different shapes of head as best as possible. It is extremely important that the same pressure is applied on each electrode all over the head, in order to have the same signal quality throughout the entire cap,” outlines Professor Comani. “For this purpose we have developed a socalled adduction mechanism, so that there is an even distribution of pressure.” This means that good-quality signals can be recorded across the cap, while the optimal
The big advantage of using dry electrodes is the ease of mounting a high-density cap and recording the EEG. If a patient is suffering an epileptic crisis, you can rapidly mount the cap and record the foci, where you think the epileptic crisis originates. If you’re interested in basic science, using dry electrodes will reduce the overall recording time. pressure level will also be more comfortable for the subject, so that the cap can be worn for longer and signals can be acquired for longer, as required for some neurological investigations. The number of electrodes in the cap may vary depending on the specific purpose of the recording, whether it’s looking to gain new insights into epilepsy for example, or monitoring how a sports team works together to achieve a shared goal. “The most useful number of electrodes in the cap depends on the application – but from the technological point of view there is no limitation on the
12
number of electrodes that you can have in a single cap,” says Professor Comani. A number of different systems have been developed within the project. “We’ve been developing systems with 8 electrodes, as they are extremely useful for sport applications. They are easy to wear and we can quickly pick up signals that are really useful for sport applications in terms of training and performance,” continues Professor Comani. A different application may require more electrodes, in which case the cap network can be adjusted to record the signals, from which scientists can learn more about how the brain performs specific tasks. This is a complex area of research, and Professor Comani says different areas of the brain may be involved in performing a specific task. “Traditionally it was thought that there are areas of the brain that are dedicated to a task, like the motor areas for example. However, in recent years it’s become clear that it’s not just one area, or a couple of areas, that are dedicated to a certain type of task – for instance motor or cognitive tasks – but rather a network of areas,” she explains. This makes it more complex to relate brain signals to specific tasks. “Analysing EEG signals typically means
analysing not just the signal recorded by one electrode, but analysing the ensemble of signals recorded by all sensors simultaneously,” says Professor Comani. “The challenge of reconstructing the activity of specific cortical sources in relation to EEG signals is related to the solution of the inverse problem: from the EEG signals produced we reconstruct the activity of the brain sources that have generated them.” There are certain mathematical techniques which can be used to decompose and re-project the EEG signal over the scalp, in order to reconstruct what sources were active at a given
EU Research
Fig. 1: Overlay plot of 5 sec of spontaneous EEG containing an eye blink artifact. Frontal electrodes L1, LL1, R1, and RR1 for a single volunteer shown. Dry and conventional recordings acquired sequentially; filtered 1-40 Hz.
Fig. 2: Overlay plot of 50 sec of spontaneous EEG containing externally triggered eye blink artifacts. Frontal electrodes L1, LL1, R1, and RR1 for a single volunteer shown. Dry and conventional recordings acquired sequentially; filtered 1-40 Hz.
ANDREA Active Nanocoated Dry-electrode for Eeg Applications Project Objectives
The scientific objective of the ANDREA project was to develop a novel dry electrode EEG system with adjustable cap network provided with an automated sensor positioning mechanism, active pre-amplification and a SW toolbox for artifacts removal. The novel technologies address the requirements of high signal quality and reliability, mobility, high patient/subject comfort and longterm use for broad EEG employment.
Project Funding time during the recording. By using these techniques in different frequency bands, researchers can investigate which brain areas were involved in the execution of a task. “Depending on what types of tasks you are interested in, you can filter off all unnecessary frequencies, those that are not of interest at that time,” outlines Professor Comani. Other physiological signals, like blinking for example, may interfere with the signal of interest in research; this is an issue Professor Comani and her colleagues in the project have been working to address. “We have developed new techniques to get rid of the interference from those artefacts, and to retain the artefact-free brain signals,” she continues. “For example, there are the so-called data-driven techniques, which consider specific characteristics of the signals, which can be used to separate the artefactual signals from the true brain signals.”
System application The system itself has been applied on both clinical and non-clinical populations, with researchers comparing it to the traditional ‘wet’ systems and aiming to assess its efficacy in certain contexts, for example evaluating patients with neurological conditions. The project has collaborated closely with a private healthcare clinic, which gave Professor Comani and her colleagues the opportunity to test the system on patients with epilepsy or dementia. “We had a cap with 64 electrodes, and we compared that to the traditional clinical ‘wet’ system, with 22 electrodes,” she explains. Both the performance of the cap and the signal quality were evaluated. “We measured the impedance between electrode and skin in both systems, and also asked patients to describe their comfort on a scale of 1 to 10 – the higher the value, the higher the discomfort. Then, from the technological point of view, we evaluated the dynamic range of the electrodes,” continues Professor Comani. “In terms of signal quality, we evaluated the signal-to-noise ratio during blinking, and eye closing and opening.” The results so far have been positive, with researchers finding that in the majority of cases
www.euresearcher.com
neurologists were able to reach a diagnosis using just the data from the dry electrodes. This could enable medical professionals to gain deeper insights into neurological conditions like epilepsy. “The big advantage of using dry electrodes is that if a patient is suffering an epileptic crisis, you can rapidly mount a highdensity cap, record the EEG signals from the cortex, and reconstruct the position of the foci, where you think the epileptic crisis originates. Whereas mounting a wet EEG system takes time, and one might miss the possibility to register the EEG during a crisis,” explains Professor Comani. This information on the foci can then inform surgery. “With EEG you can localise the foci of the epilepsy. Those foci can be ablated, but if you don’t have a recording during the epileptic crisis then you have to provoke a crisis in a patient in order to localise the foci,” says Professor Comani. “Using dry electrodes would mean that you could easily record the EEG, and therefore be able afterwards to localise the epileptic foci, without having to provoke an epileptic crisis in the patient.” Researchers are also looking to apply the system on non-clinical populations, one of which is a team of basketball players. Acquiring EEG signals from a team, during either a match or practice, could allow scientists to analyse how they work together. “The players have different roles within the team, but they’re all working towards the shared goal of winning the game. They behave collaboratively,” points out Professor Comani. Many theories have been suggested to describe how team members interact, but they have not always been substantiated by quantitative measures of brain activation within each member; this is an area of great interest to Professor Comani. “This is extremely interesting from the scientific point of view, to see these so-called functional connections between different subjects, which are not supported by anatomical connections. Functional connections are found at a frequency level, in the recorded signals,” she says. “Social neuroscience is a potential field of application for the ANDREA system, the field would greatly benefit from this technology.”
ANDREA is an EU-funded FP7-PEOPLE Marie Curie Industry-Academia Partnership and Pathways (IAPP) project running from January 1, 2014 until December 31, 2017.
Project Partners
The ANDREA consortium merges the complementary expertise and resources in biomedical engineering, material science, biomedical signal processing, neuroscience and clinical neurology available at 3 academic partners (BIND Center at the University of Chieti, Italy - Coordinator, BMTI at the Technische Universitaet Ilmenau, Germany, the Faculty of Engineering at the University of Porto, Portugal), one industrial partner (eemagine Medical Imaging Solutions GmbH, Germany) and a private hospital (Casa di Cura Privata Villa Serena, Italy).
Contact Details
Professor Silvia Comani, PhD Coordinator - EU Project ANDREA Department of Neuroscience, Imaging and Clinical Sciences University “G. d’Annunzio” of Chieti-Pescara Via dei Vestini, 33 66013 Chieti Scalo - Italy T: +39 0871 3556925 E: comani@unich.it W: www.andreaproject.eu Professor Silvia Comani, PhD
Silvia Comani, PhD is Associate Professor of Applied Physics and Director of the BIND – Behavioral Imaging and Neural Dynamics Center. Professor Comani received the Italian at the Degree of Doctor in Physics in University of Bologna (Italy), and the PhD degree in Physics in at the Catholic University of Louvain-la-Neuve (Belgium). Her main research interests are the development of novel methods for the analysis of biomedical signals and their application in neuroscience. She is author of more than scientific articles published in international peer-reviewed scientific journals, and serves as reviewer for international peerreviewed scientific journals.
1979
1985
100
27
13