As it takes several seconds for the blood flow to change, and the actual recording is limited by computational factors, the data collection is slowed down. One drawback with fMRI is the temporal resolution. This is the data that we see with fMRI, often visualized over an MRI image.
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This is known as the Blood-Oxygenation Level Dependent response (otherwise known as BOLD). If there is more oxygenated blood in one part of the brain compared to others, then chances are that this brain area is more active. A certain part of my brain will increase its activity to send the message to complete this action, and that area of the brain will receive ever-so-slightly more oxygen-rich blood.įor fMRI, the same things happen as with MRI – the energy emitted from the relaxation of protons is measured – but the calculations are instead aimed at determining how the amount of oxygenated blood flow changes. If I want to move my right arm, a few things need to happen. So how can we get an image of the brain activity? This is where fMRI comes in. Of course, MRI only shows us a static image of the brain – an anatomical image, not of the brain’s actual activity. Through some calculations (that are beyond the scope of this blog post, but see here: ), the computer can determine what the tissue looked like, depending on this energy that is released, and show us an image of the tissue. This is the crucial bit – as the protons relax, energy is released which can be detected by sensors in the MRI machine. But, as the radio frequency only happens for a moment, the protons relax back to their aligned state before. This also interacts with the protons, essentially turning them to the side. Phew.įor the next step, a radio pulse is emitted (just like a normal radio signal, just much quicker). So, we’re lying in the MRI machine, and the protons in the hydrogen atoms (that are in the water in our body), are mostly pointing the same way. Usually, these protons are facing in random directions, but the magnetic field makes a significant portion of them align in the same direction. The magnetic field from the MRI interacts with the protons in our hydrogen atoms (it’s of course pretty handy that we are 70% water – there are plenty of hydrogen atoms for the magnet to affect). MRI is a complex imaging methodology, but we’ll try to give you an overview here.Īs the name suggests, magnets are central to magnetic resonance imaging, but quite a bit stronger – roughly 1,000 to 3,000 times stronger than the average fridge magnet. This structural information can be useful for determining how the sizes of certain brain areas compare across people, or if there is something abnormal about a particular brain (a tumor for example). MRI (magnetic resonance imaging) provides a map of the brain – how it looks at a set moment in time.
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Check out: What is EEG and How does it Work What is MRI? ), but it remains a challenge for EEG research. There are calculations that can be applied that attempt to get around this limitation (e.g. A computer then receives this signal, and can generate various maps of brain activity, with a rapid temporal resolution.Ī drawback for EEG is the spatial resolution – as the electrodes measure electrical activity at the surface of the brain, it is difficult to know whether the signal was produced near the surface (in the cortex) or from a deeper region. The signal from the electrodes is then sent to an amplifier, that (no surprises here) amplifies the signal. The electrodes of an EEG headset can’t detect changes in single neurons, but instead detect the electrical changes of thousands of neurons signalling at the same time. The more electrical signals, the more neuronal communication, which corresponds to more brain activity. The brain is an electrical system – all of our thoughts (conscious or otherwise) are generated through a network of neurons, that send signals to each other with the help of electrical currents. This can be useful for quickly determining how brain activity can change in response to stimuli, and can also be useful for measuring abnormal activity, such as with epilepsy. It tells us, from the surface measurements, how active the brain is.
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What is EEG?ĮEG (electroencephalography) measures the electrical activity of our brain via electrodes that are placed on the scalp. This needn’t be as gruesome as it sounds, as many brain imaging methods today are entirely noninvasive.īelow we will go through the most common brain imaging techniques – EEG, and (f)MRI, to see how they work, and how they compare, looking at the advantages and disadvantages of each. Understanding human thought and behavior can take many approaches, but to really understand how the brain works, you need to look inside it.