A volunteer is fitted with a 64 channel EEG cap
Electroencephalography /EEG is one of the most popular ways of measuring your brain's electrical activity noninvasively. EEG records the electrical fields produced in the brain via electrodes placed on the head/scalp. The electric fields result from electrochemical signals passing between neurons and when billions of these tiny signals pass simultaneously in a geometrically aligned neural population, the field strength becomes strong enough to be measured outside of the head. Research has suggested that not all electric field produced by the brain is strong enough to reach the scalp. Mainly, the synchronized activation of pyramidal neurons is the main contributor to EEG.
Some of the advantages they have over other recording modalities are a) high temporal resolution, b) portability, c) non-invasive nature, and d) being a relatively inexpensive measurement modality.
The electrical activity in the brain can be measured in different scales and to give an analogy, single-unit activity (action potentials) is akin to a one-on-one interview of a journalist inside a football stadium. Local field potentials which measure a population of neurons are like capturing commentators on a football match in a press box. EEG on the other hand is like how the cumulative sound gets heard from outside the stadium. The following figure from Biasiucci et al. 2019 summarizes this.
Photo credits: Biasiucci, Andrea, Benedetta Franceschiello, and Micah M. Murray. "Electroencephalography." Current Biology 29.3 (2019): R80-R85.
The polarity of the signal measured at the scalp depends on the particular orientation of the population of neurons as shown below. No clear dipole would emerge if the pool of population neurons is arranged randomly such as in figure c or the positive and negative pools cancel each other out if arranged like figure b. Figure a depicts the situation of how an ideal pool would look like.
Photo Credits: Jackson, Alice F., and Donald J. Bolger. "The neurophysiological bases of EEG and EEG measurement: A review for the rest of us." Psychophysiology 51.11 (2014): 1061-1071.
Cognioinics System
As a recording modality, we made use of the Quick 20 EEG headset from Cognitionics which is a 20 channel dry EEG headset. In addition, the headset also houses an accelerometer to measure the head movements of the participant. The mobility and versatility of Cognionics’ headset allow measuring the brain outside of the laboratory in action and in context.
