6 ways to measure brain activity
There are plenty of methods to capture information on brain structures and functions. Some of them are safer than the others; some involve difficult techniques while others are quite simple in their execution; some are quite expensive and some you can perform every month. All of them are used to collect valuable data about our brain activity, which helps to determine conditions and disease that would be hard to diagnose in any other case. Let us look closely what available methods of brain scanning are available in the modern medicine.
1. Electroencephalography (EEG)
EEG allows neural specialists to analyze brain activity by measuring electrical activity that is generated in the different cortical layers of the brain. Electrical signals are picked up from the gray matter areas with high densities of pyramidal cells which communicate with each other. During the communication process these cells are ignited in a synchronized patter and the generated electricity radiates to the skull surface, where EEG electrodes are attached. Specialists need to amplify these signals, since they are still very subtle. Before scanning process they take a measurement of the “reference location” (usually these are the areas behind your ears) and then compare the activity of other zones to that control measurement. 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 ms dependent on the sampling rate). EEG allows you to record brain processes that occur shortly after the onset of visual or audio 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 that occurs over longer periods, like hours or even days. This phenomenal time resolution gives you insights on the precise timing of brain activity.
2. Functional magnetic resonance imaging (fMRI)
fMRI is a functional neuro-imaging procedure measuring brain function by picking up changes in blood flow associated with neural activity. The main theory is that neurons require 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.
3. Computed tomography (CT)
CT scanning projects a picture of the brain based on the differential absorption of X-rays. During the scan process patient lies on a table which slides into a cylindrical apparatus. The beam of x-ray passes the patient’s head and then machine’s detectors sample it particles. Images made using x-rays depend on the absorption of the beam by the tissue it passes through. Bone and hard tissue absorb x-rays well, air and water absorb very little and soft tissue is somewhere in between. Thus, CT scans reveal the gross features of the brain but do not resolve its structure well. As you can see CT scan is mostly like an x-ray image of brain, therefore it cause a little bit of radioactive exposure and cannot be performed too often.
4. Magnetoencephalography (MEG)
The main difference between EEG and MEG is that with EEG the data is being gathered in the form of electrical activity generated by neural firing, when in the case of MEG it is magnetic fields. MEG devices are completely stationary like fMRI devices. For the most precise results patient are required to lay or sit motionless with their head fixed. In order to prevent other magnetic fields leaking into the data recording and interfere with the results, patients are protected by a shielded chamber. The biggest advantage is that MEG combines the high precision in time of the EEG with the high precision in space of the fMRI, so it’s the best out of the 2 worlds. 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.
5. Positron Emission Tomography (PET)
PET use sugar glucose levels in the brain to measure and demonstrate neural firing sites. The way it works is because of the fact that active neurons use glucose as energy source for signal transition. During the scan process a tracer substance attached to radioactive isotopes is injected into the blood. Blood with tracers is sent to deliver oxygen into the parts of brain that become active at that time. This creates visible spots of activity, which are picked up by detectors and projected onto the screen as video image of the brain performing a certain task. Unfortunately, PET allows us to see only general areas of brain activity and not specific locations. In addition, PET scans are costly and invasive, making their use limited. However, they can be used in some forms of medical diagnosis, including for Alzheimer’s.
6. Near infrared spectroscopy NIRS
NIRS is a safe optical technique to measure activity by evaluating blood oxygenation in the brain. A bright ray of light in the near infrared spectrum (700-900nm) scans through the skull and detects the attenuation of remerging light. Blood oxygenation affects this light attenuation and this data is collected in order to indirectly measure brain activity. It’s not the most accurate or informative way, but definitely the most harmless and easy for the patient.