The world's first whole-head child MEG system

In July 2008, the world's first whole-head child MEG system was installed at the KIT-Macquarie Brain Research Laboratory. This laboratory is part of the Macquarie Centre for Cognitive Science (MACCS). The new child MEG system adds to an adult MEG system that was launched in 2006. The adult MEG system is the first of its kind in the Southern Hemisphere. With the new child system, the KIT-Macquarie Brain Research Laboratory is the first lab in the world to house two MEG systems in the same location.

What is MEG?

MEG is shorthand for magnetoencephalography, so you see why we simply call it 'MEG.' MEG is a brain imaging technique that measures the magnetic fields generated by the human brain whenever information is being processed. The brain's magnetic fields are 100 million times smaller than the earth's magnetic field, and 1 million times smaller that the magnetic fields produced in an urban environment such as North Ryde, so the MEG system is situated in a multi-tonne shielded room with thick metal walls designed to block out the external magnetic fields. Importantly, the MEG system is a 'passive' device and is not harmful in any way. The new child MEG system is a revolutionary technological advance - a whole-head system that has been designed especially for children's smaller head sizes. The design of the system ensures that the 64 sensors that measure children's brain activity are positioned close enough to the child's head to make accurate measurements of ongoing activity, with millisecond accuracy. This allows us to accurately record the magnetic signals that are produced in the brain while a child is performing a cognitive task, or just listening to speech or looking at visual images.

What is special about MEG?

Among the more familiar brain imaging techniques are fMRI and EEG. fMRI ('functional magnetic resonance imaging') measured changes in blood flow, so this is a 'hemodynamic' technique. This technique offer good spatial resolution, but the temporal resolution of such methods is only on the order of seconds, since they measure neural activity indirectly. This brings us to EEG, which is short for 'electroencephalography.' EEG measures electrical activity produced by the brain as recorded from electrodes placed on the scalp. EEG provides exquisite timing resolution, and has been used to study neural processing during language comprehension, but EEG cannot tell us where in the brain these important events are taking place. EEG also requires extensive set-up time for the electrodes to be fitted to the scalp.

Like EEG, MEG provides exquisite timing resolution. In addition, however, MEG also has excellent spatial resolution, so it enables us to find out both when and where in the brain information is being processed. MEG allows completely non-invasive measurements of neuronal activity in the brain, by recording magnetic fields at different sites around the head. Using MEG, measurements can be taken without the need for electrodes to be placed on the child's scalp, as with EEG. This means that without any discomfort and very little set-up time, a child can be positioned inside the MEG and we can begin measuring the changes in magnetic fields generated by his or her brain. Until now, the size of the available MEG systems made it difficult to obtain good brain signals from children, so this new child MEG system is a significant technical advance, enabling us to conduct research with children, including special populations such as children with autism, or children who are poor readers. 

What can MEG tell us about Children's Cognitive Processing?

The first research projects using the child MEG system will study cognitive processing and processing of language in normally developing children. Using MEG, we expect to make major advances in our understanding about children's knowledge of language. Among the early studies will be investigations of the time course and location of brain responses of children as they perform different linguistic tasks such as listening to words or sentences. The data from these initial studies will establish baseline measures for future studies with special clinical populations including children with autism, dyslexia or specific language impairment.

Here is an example of a study that is underway. The study compares sentences such as the ones below. These sentences differ only by a single word: the (a) example contains nobody whereas the (b) example contains everybody. The targeted word in both sentences is any. In the (a) example, with nobody, the word any fits nicely. However, if everybody is used instead, this suffices to make the word any seem out-of-place in example (b), as indicated by the asterisks. 

a) Nobody at the party ate any of the snacks.

b) Everybody at the party ate ***any of the snacks.

This is just a single example from English, but the same thing happens in other human languages, e.g., Chinese, Russian, Italian, etc.

Our research question is this: Do very young children know that the word any is fine in the (a) example, but not in the (b) example?  Until the advent of brain imaging techniques, it has been impossible to answer this question, and many others like it, because children younger than 4- or 5-years old cannot perform the kinds of psychological tasks that are used to assess linguistic knowledge in adults, such as deciding if a sequence of words forms a 'fine' (well-formed) sentence or not. Brain imaging technologies are particular promising in overcoming this difficulty because they circumvent, at least in part, the barriers to direct experiment. Using MEG, we can measure how a child's brain responds to examples like (a) and (b) above, without asking the child to make any conscious decisions about what they are hearing.

MEG Research with Special Populations

Much of our research with children and other special populations also takes advantage of the fact that MEG can measure brain responses without asking subjects to perform any behavioural task, such as deciding if a sequence of words makes a 'good' sentence.  This feature makes the child MEG system especially valuable for research on certain clinical populations. For example, MEG will be a valuable tool in the study of children with autism, who characteristically have considerable difficulty with communication. Research investigating the linguistic knowledge of autistic children is already being planned by MACCS researchers Dr. Blake Johnson and Dr. Jon Brock. MEG measurements will investigate the ways in which language areas of the brain connect with other areas of the brain, to see if these connections are different in autistic children as compared to normally developing children, as predicted by some current theories of autism. 

MEG may also yield insights into the neural basis of stuttering. Dr. Johnson and Professor Crain at MACCS are collaborating with Dr. Elisabeth Harrison at the Macquarie Speech Clinic to investigate problems in how speech output is controlled in young children who stutter. Stuttering is a problem of speech output that is often manifested when children first begin to combine words into simple sentences. It is thought to involve problems in those brain areas that coordinate the muscles used in speech production.

MEG Research on Visual Processing

The child MEG system also has the potential to make a huge impact on research into how the brain processes visual information. Dr Mark Williams will be using the child MEG to further our understanding of how we perceive faces and objects. Although we have mapped the brain regions involved in face and object perception in adults, we know much less about how these regions develop in children. Dr Anina Rich plans to examine the way in which we develop control over our attention, a process that is fundamental to successful functioning in daily life. Children rapidly develop the ability to ignore salient but irrelevant information, and concentrate on essential information. This ability plays a critical role in children's capacity to learn at school and throughout life. Dr Rich has been studying these processes in adults. She will now be able to explore these processes in the developing brain.

Future Directions in MEG Research

The capability to bypass conscious decision-making is the basis of another new venture using MEG -- research into hearing disorders. Macquarie's Centre for Languages Sciences and several local hearing organizations -- Cochlear Ltd., the National Acoustic Labs, the HEARing CRC -- are collaborating on the development of a third MEG system to assist in the rehabilitation of individuals who receive cochlear implants, including young children. Recipients of a cochlear implant receive extensive rehabilitation to recognize the sounds of speech. At present, hearing is assessed by asking the recipient of the cochlear implant to report their subjective impressions of sounds. This is a difficult and frustrating process for adults, and children younger than 3- or 4-years old are unable to perform this feat at all. This is unfortunate because children are more likely to successfully develop hearing and language skills when implantation is early in life, and currently cochlear implants are being fitted to babies as young as 3 months old. To overcome the difficulty in assessing how children are perceiving sounds, the new MEG system will be the world's first measurement device to provide objective measures of how recipients of a cochlear implant, including young children, hear the sounds of speech.

How is the MEG Laboratory Funded?

The child MEG system is funded, in part, by an Australian Research Council Linkage Industrial Partner Grant (LP0669471). This grant was awarded to Macquarie researchers (Professors Stephen Crain and Max Coltheart and Dr. Rosalind Thornton) and to Professor Hisashi Kado, Director of the Applied Electronics Laboratory at the Kanazawa Institute of Technology in Japan. In developing the child MEG system we also received generous financial support from the Yokogawa Electric Co., the industrial partner of the Kanazawa Institute of Technology. Additional funding for MEG studies has been awarded as part of the HEARing CRC, and the National Acoustic Labs is working with us to refine the systems for precise presentation and analysis of speech sounds. The availability of the adult and child MEG systems was instrumental in recruiting several cognitive neuroscientists to the Macquarie Centre for Cognitive Science, and we are actively recruiting researchers to the newly-formed research centre, the Centre for Language Sciences.