Functional Magnetic Resonance

First introduced in the 1990s, fMRI (functional magnetic resonance imaging) is used to map the brain by providing 3D neuroimages showing areas of activity. The patient is placed in a tube-shaped machine that uses incredibly powerful electromagnets to scan the body and brain.

fMRI machine with a patient, Thomas Angus, Wikimedia Commons

In 1993, fMRI was mentioned less than 20 times in published articles. As a new technique, it developed rapidly, and by 2003 that number was about 1800 (Berman et al. 2006). There could be several reasons for this. We believe it was due to the novel and interesting methods scientists began to use to study the brain with fMRI and how they used this technique to determine the brain’s functions as a whole.

How does functional magnetic resonance imaging work?

Functional magnetic resonance imaging detects changes in blood oxygenation in the brain, the flow of which brain activity affects. When an area of the brain is more active because the participant or patient being observed is doing something, such as working on a task, or because of damage, the brain blood flow will increase or decrease based on oxygen demand.

Haemoglobin supplies oxygen to neurons. When these neurons activate, the increased activity must be balanced by providing the necessary oxygen and blood flow to make this possible. Blood with a higher oxygen concentration is affected differently by magnetic fields than blood with lower oxygen content. The fMRI magnetic field can detect this when scanning the participant or patient. This is called the BOLD (Blood oxygenation level-dependent) signal or theory and is primarily responsible for how an fMRI identifies functional areas.

An fMRI will then map the activated areas using voxels (when creating a 3D image of the brain, a voxel unit represents a tiny portion of brain tissue in the image), producing neural images, as seen below. The highlighted areas are active parts of the brain, in this case, someone working on a memory task while sitting in the machine.

fMRI scan during working memory tasks, Wikimedia Commons

Interestingly, a participant or patient must not speak or otherwise communicate when thinking about a task or answering a question. They have to answer it internally to prevent the brain from activating in other areas. Suppose the participant answers a question about a memory task out loud. In that case, the motor cortex (getting the body and muscles to speak) and the language areas (Broca’s and Wernicke’s areas) could activate and deactivate, messing up the results.

A good example is a study by Downing et al. (2001) in which they used fMRI to assign a function to specific brain regions:

• There is evidence that the human visual cortex regions respond specifically and selectively to faces.
• Downing et al. (2001) wanted to find out if this was also true for other regions responding to human body images and not just to faces.
• They found that cortical regions in the brain do indeed respond selectively to images of the human body, particularly the lateral occipitotemporal cortex, and that a specialised neural system exists for visual perception of the human body.
• The use of fMRIs made all these discoveries possible!

Similarly, Haxby et al. (2001) studied the architecture of the object visual pathway in the brain using fMRI:

• They measured the ventral temporal cortex patterns while subjects looked at faces, cats, nonsensical pictures, and artificial objects.
• They found distinct pattern responses for each category.
• Overall, they found that representations of faces and objects in the ventral temporal cortex were widely distributed and overlapping.
• They identified these functional areas thanks to the use of fMRI.

By using this brain scanning technique to identify potential functional areas, we can say that certain behaviours could be due to these functional areas. We can assume that an area of the brain that ‘lights up’, so to speak, correlates with the actions and behaviours of the individual, especially if we are careful in our experiments of isolating specific stimuli.

Evaluation of functional magnetic resonance

What are the advantages of functional magnetic resonance imaging? How about its weaknesses in studying the brain?

Strengths

• Non-invasive: An fMRI does not involve inserting anything into the brain or cutting open the head to look at the brain itself. It provides a view of the brain and its activities without invasive techniques.

• Virtually no associated risks: Because fMRI does not require any of the invasive techniques mentioned above, it is already safer than those techniques. It also does not use radiation, used in other brain-scanning techniques such as the PET scan (positron emission tomography).

• Clearly illustrates localisation: Neuroimages show clear areas of activity related to the patient’s or participant’s activity and are robust in studies that focus on examining a specific function, limiting confounding variables.

• Helps prepare for surgery: If a patient needs surgery, fMRI is valuable beforehand to map areas needing attention to better prepare and navigate efficiently during surgery.

• High spatial resolution: It provides a detailed image and is extremely accurate.

Weaknesses

• Expensive: Operating an fMRI machine is quite costly, both in training and the machine itself.

• Stillness required: A participant or patient must remain still while scanning in the machine, severely limiting the type of research with this method. They cannot move, respond properly, or perform tasks that require movement, as this would compromise the results or make scanning impossible altogether.

• Blood flow is difficult to interpret: Because an fMRI only detects changes in blood flow, it can only tell you if an area is active or not. It does not tell you why the neurone in question is activated, nor does it tell you anything beyond changes in blood flow. The neurone itself can be activated for various reasons, with different tiny functions controlled by the primary function. Therefore, it is impossible to determine the cause and effect.

• Some areas also light up for multiple reasons. Certain areas of the brain are responsible for reactions that can be opposite, especially when it comes to emotional responses.

• Low temporal resolution: there is a slight delay, usually about five seconds, before changes in blood flow and activity levels within a neurone are detected, so fMRI has a poor temporal resolution.