Science Show: Functional Brain Imaging
1st December 2014
If you tuned into the Science Show this week, you’ll have heard Dr. Matt Brookes and Professor Peter Liddle discussing their work in particular fields of functional brain imaging. If you missed out on the show, or simply want to find out more, then you’ve come to the right place!
Before we go into specifics, we should probably ask; what is functional brain imaging? Often referred to as neuroimaging, FBI is a blanket term used to describe a variety of techniques for ‘looking’ inside the brain (without the need for slicing and dicing). Applications range from measuring blood oxygenation in certain regions of the brain, to studying the effects of excessive drinking/ smoking/recreational drug use on your grey matter.
As previously mentioned, there are several different kinds of functional brain imaging, all of which differ slightly in methodology. Together, they can provide a vast wealth of information about the brain. Examples include:
• Functional Magnetic Resonance Imaging (fMRI): A technique similar to MRI, fMRI measures brain activity by detecting changes in blood flow, working off the principle that blood flow to a particular region of the brain increases when that region is in use. fMRI has dominated brain-mapping research since the early 90’s, but clinical use is lagging behind; while often used to assess the risk in brain surgeries or to learn how an injured brain may be functioning, tumours and lesions can affect blood flow in a way completely unrelated to neural activity, as can substances as commonplace as caffeine. This can greatly interfere with fMRI. Despite this, the technique has been quite successful in testing the effectiveness of certain behavioral therapies, and detecting early onsets of Alzheimer’s and depression.
• Electroencephalography (EEG): The recording of electrical activity along the scalp. By measuring voltage fluctuations within the neurons of the brain, EEG is most commonly used to diagnose epilepsy, sleep disorder, and in certain cases, brain death. The first human EEG was recorded in 1924 by German physiologist Dr. Hans Berger, in what was described as ‘one of the most surprising, remarkable, and momentous developments in the history of clinical neurology’. Largely developed from the work of Richard Caton towards the end of the 19th century (on electrical activity in the brains of rabbits and monkeys), EEG is now a popular method of neuroimaging. However, the technique is not without its disadvantages; as thousands of electrical signals need to be averaged out, a routine EEG takes around half an hour. In some cases, (particularly during seizures), patients must be recorded for days, or even weeks. On top of that, neurons deeper within the brain contribute very little to the EEG signal, and therefore an EEG cannot be used to provide statements regarding ‘global brain activity’. Cerebrospinal fluid in the brain can also interfere with an EEG signal.
• Magnetoencephalography (MEG): The main topic of Dr. Brooke’s research, MEG maps brain activity by recording magnetic fields produced by electrical currents that occur naturally in the brain. Using ‘superconducting quantum interference devices’ (often known as SQUIDS) as basic magnetometers, MEG is used to provide basic research into cognitive processes, and identify regions of the brain affected by illness/disease, before preparing for surgical removal. As the magnetic signals produced by the brain are so small (in the femtotesla region), the equipment must be shielded from any external magnetic fields (including the Earth’s). As such, MEG is conducted inside a magnetically shielded room, protected by three distinct layers. Each layer consists of one pure aluminium section, and a high-permeability ferromagnetic section. The innermost layer is the most shielding. One of the most significant problems with MEG (often known as the ‘inverse problem’) arises from using the magnetic fields outside the head to determine the location of electrical activity within the brain. Without a suitable number of constraints, there is no unique solution, meaning there are a potentially infinite number of ‘correct’ answers. Certain solutions can be eliminated using models based on prior knowledge of brain activity.
• Many other neuroimaging techniques were discussed in this week’s Science Show (such as Near-Infrared Spectroscopy and CT scans), and there are many others that exist besides.
Whether or not these techniques will ever be capable of ‘reading thoughts’ is an oft-debated topic. Most recently, a group of researchers from the University of California have been working on a ‘brain decoder’, capable of translating people’s innermost thoughts. This was accomplished by examining the brain activity of seven individuals undergoing epilepsy surgery, both while they were reading aloud and while they were reading in their heads. By locating the ‘firing’ neurons and identifying neuronal firing patterns, a personalized decoder was developed for each individual. This produced a visual representation of the sound waves produced, and because specific frequencies could be connected to specific sounds, the decoder was able to translate a few of the words that were thought. The ultimate goal for this kind of technology is to provide a means of communication for the paralysed and otherwise mute, and while these initial results are promising, the algorithms are nowhere near accurate enough to achieve this goal. According to lead author Brian Pasley, the next step is to ‘improve the algorithm by looking at brain activity during different pronunciations of words and speeds of speech’.
So there you have it; functional brain imaging shows promise in both clinical and research fields. Used to identify conditions such as schizophrenia, ADHD, and depression, as well as isolate areas of the brain affected by certain ailments, FBI has saved, or at the very least extended, countless lives, and will continue to do so for many years into the future. At the very least, it seems we’re a far cry from the Government browsing freely through our heads to look up thoughtcrime.