The Music of MEG

Every Christmas back home in Finland, the Martinos Center’s Matti Hämäläinen gathers with friends for an evening of performing chamber music. He plays both flute and piano on these occasions. In more recent years he has explored the repertoire for “piano four hands” with his former classmate Lauri Malmi, now a professor of computer science at their alma mater, Aalto University (formerly Helsinki University of Technology). Whatever the instrument or configuration of musicians, Hämäläinen appreciates the combination of talent, skill and inter-player cooperation that goes into a successful performance. Not only do you need to play well, you need to play well together. Only then can you make truly beautiful music.

Very much, he says, like doing science at the Martinos Center.

Hämäläinen is director of the David Cohen Magnetoencephalography (MEG) Laboratory at the Martinos Center, working alongside faculty members Steven Stufflebeam, Seppo Ahlfors, David Cohen and Sheraz Khan. Over the past nearly two decades, the researchers have played a crucial role in developing MEG instrumentation, analytical methods and tools, and experimental protocols, and collaborated with others in the Center and elsewhere both in integrating MEG with other imaging modalities and advancing it for a broad range of applications. Together, they have paved the way for MEG to become an important basic research and clinical tool worldwide.

What Exactly Is MEG?

Magnetoencephalography records changes in the very weak magnetic fields surrounding the human head that are caused by electrical activity associated with neuronal currents underlying brain function. The technique offers excellent temporal resolution—on the order of milliseconds—and thus provides a more direct measure of neuronal currents than other imaging modalities, including functional magnetic resonance imaging (fMRI), which derive information about neuronal activity from the much slower neurovascular response.

Above: the MEG group in the early 2000s. In the photo at the top of the page: Matti Hämäläinen (left) plays a duet.

The technique was introduced more than 50 years ago by MIT researcher David Cohen, who is now a faculty member at the Martinos Center. Cohen developed a way to isolate and record the weak magnetic fields emanating from the human body by using a magnetically shielded room built around the recording equipment. On New Year’s Eve, 1969, using a superconducting quantum interference device (SQUID) developed by researcher James Zimmerman while he was working with the Ford Motor Co., Cohen successfully recorded the biomagnetic signal from Zimmerman’s heart. He later applied the technique to the brain, facilitating use of MEG for a range of neuroscience studies.

Hämäläinen’s accomplishments, both before and after the introduction of the whole-head MEG device, caught the attention of the Martinos Center’s Jack Belliveau, who in the mid- to late 1990s was traveling the world seeking out researchers with whom to develop multimodal imaging technologies to delve even deeper into the brain. The pair subsequently launched a fruitful collaboration.

In the early days of MEG, researchers used either one or several devices called magnetometers to localize electrical activity in the brain. Because these measurements used so few sensors and allowed only small coverage of the brain, researchers had to obtain recordings from multiple locations on the head, making the procedure impractical for routine clinical use. Later, investigators introduced multi-channel MEG systems with enough coverage to localize activity in a registered MRI scan of the brain. In 1992, the first whole-head MEG device, with more than 100 channels, was completed by a team at Helsinki University of Technology—a team that included Matti Hämäläinen. The device was a major breakthrough in the field, opening the door to any number of new types of studies and sparking the imaginations of neuroscience researchers worldwide.

Belliveau was also working with others in the multimodal imaging space: among them, Gregory V. Simpson and his postdoctoral fellow Seppo Ahlfors from Albert Einstein College of Medicine, and Risto Ilmoniemi— Ahlfors’ PhD advisor—and colleagues from Helsinki University of Technology (Hämäläinen’s alma mater) and Helsinki University Hospital.

Seppo Ahlfors (rear left) and students during construction of the magnetically shielded room

In about 2000, the Martinos Center decided to launch an MEG program of its own. The first recruits were Ahlfors and neuroscientist and MEG researcher Eric Halgren. Hämäläinen joined in 2001. Cohen was already on board overseeing the construction of a new high-performance magnetically shielded room for the MEG—more than 30 years after he had introduced the modality a couple of miles down the road at MIT.

By 2002, the scanner was up and running and the members of the MEG group were further developing both the hardware and the data analysis tools and collaborating with researchers to apply MEG to a range of different studies. Ahlfors recalls, for example, studies of reading disability in children (Maria Mody and colleagues); studies of the human auditory and multisensory cortex (Belliveau, Jyrki Ahveninen, Iiro Jääskeläinen, Tommi Raij and others); studies of language and memory (Halgren with Ksenija Marinkovic, Anders Dale and others); and studies of obsessive-compulsive disorder (Kristina Ciesielski and colleagues). At the same time, clinical studies of patients with epilepsy were conducted with Steven Stufflebeam and colleagues.

In facilitating such studies over the years, in developing cutting-edge technology and applying it in seemingly countless creative ways, the program has always run like a welloiled machine, its members working together in perfect tandem.

Or perhaps like a chamber group, playing the music of MEG.