Mind Hacks

Hack #4. Functional Magnetic Resonance Imaging: The State of the Art

fMRI produces high-resolution animations of the brain in action.

Functional magnetic resonance imaging (fMRI) is the king of brain imaging. Magnetic resonance imaging is noninvasive and has no known side effects—except, for some, claustrophobia. Having an MRI scan requires you to lie inside a large electromagnet in order to be exposed to the high magnetic field necessary. It’s a bit like being slid inside a large white coffin. It gets pretty noisy too.

The magnetic field pushes the hydrogen atoms in your brain into a state in which they all “line up” and spin at the same frequency. A radio frequency pulse is applied at this exact frequency, making the molecules “resonate” and then emit radio waves as they lose energy and return to “normal.” The signal emitted depends on what type of tissue the molecule is in. By recording these signals, a 3D map of the anatomy of the brain is built up.

MRI isn’t a new technology (it’s been possible since the ’70s), but it’s been applied to psychology with BOLD functional MRI (abbreviated to fMRI) only as recently as 1992. To obtain functional images of the brain, BOLD (blood oxygen level dependent) fMRI utilizes the fact that deoxygenated blood is magnetic (because of the iron in hemoglobin) and therefore makes the MRI image darker. When neurons become active, fresh blood washes away the deoxygenated blood in the precise regions of the brain that have been more active than usual.

While structural MRI can take a long time, fMRI can take a snapshot of activity over the whole brain every couple of seconds, and the resolution is still higher than with PET [[Hack #3]]. It can view activity in volumes of the brain only 2 mm across and build a whole map of the brain from that. For a particular experiment, a series of fMRI snapshots will be animated over a single high-resolution MRI scan, and experimenters can see in exactly which brain areas activity is taking place.

Much of the cognitive neuroscience research done now uses fMRI. It’s a method that is still developing and improving, but already producing great results.

Pros

• High spatial resolution and good enough time resolution to look at changing patterns of activity. While not able to look at the changing brain as easily as EEG [[Hack #2]], its far greater spatial resolution means fMRI is suitable for looking at which parts of the brain are active in the process of recalling a fact, for example, or seeing a face.

Cons

• Bulky, highly magnetic, and very expensive machinery.

• fMRI is still new. It’s a complex technique requiring computing power and a highly skilled team with good knowledge both of physics and of the brain.

—Myles Jones & Matt Webb