There are many different methods to go about capturing information on brain structures and functions. The three most common and most frequently used measures are functional Magnetic Resonance Imaging (fMRI), magnetoencephalography (MEG) and electroencephalography (EEG). Of these methods, EEG is the most versatile and cost efficient solution.
When using EEG, you are measuring electrical activity generated by the various cortical layers of the human brain. Specifically, electrical signals are picked up from gray matter regions, which have high densities of pyramidal cells that communicate with each other. Whenever large groups of these pyramidal cells are firing up in a synchronized pattern, the generated electricity radiates to the scalp surface – this is what we record with EEG electrodes. Because the electric fields are still very low, signals are generally amplified.The activity will be stronger compared to a reference location (typically located behind the ears referred to as the left/right “mastoid processes”). Keep in mind that EEG is a referential recording and not an absolute voltage – it always represents a relative increase or decrease in electricity at the specific location. The changes in electric fields occur very fast – so with EEG you will get insights into brain processes with a very high time resolution (up to 1 millisecond dependent on the sampling rate). EEG allows you to record brain processes that occur shortly after the onset of visual or auditive stimuli (there are consistent brain processes already after 50-100 ms post-stimulus), but you can also monitor brain states reflecting engagement, motivation or drowsiness over longer periods (hours to days). This excellent time resolution gives you insights on the precise timing of brain processing.
Functional Magnetic Resonance Imaging (fMRI):
fMRI is a functional neuroimaging procedure measuring brain function by detecting changes in blood flow associated with neural activity. The assumption is that neurons need more oxygen when they’re active. Because blood flow is slow, fMRI is known to have low time resolution. However, the central strength of magnetic resonance imaging is its excellent spatial resolution.
Typically, respondents have to lay motionless in a magnetic core while a superconducting magnet is rotating with high frequency around the body. fMRI then measures the change in magnetization between oxygen-rich and oxygen-poor blood, showing relative activity of different brain regions. Also, very high resolution images of brain structures can be created with an exceptional level of accuracy. With magnetic imaging you can reconstruct the individual skull shapes and cortical layers of all of your respondents.
While EEG is recording the electrical activity generated by neural firing, MEG captures the magnetic fields generated by neural activity. MEG devices are completely stationary (similar to fMRI devices). They require the participant to lay or sit almost motionless and keep movements to a minimum. MEG measures usually need to take place in a shielded chamber to avoid magnetic fields from the outside to interfere with the data recording. The biggest advantage is that MEG combines the high precision in time of the EEG with the high precision in space of the fMRI. In the end you get a precise picture of the time resolution of the signal, meaning you will know exactly which areas are active and at the same time you will know the structure of the skull and the brain very precisely.
If you would like to know more about different technologies that can measure brain activity or you have any other questions regarding biometric research please feel free to contact us.