The mysterious relationship between human behaviour and the way our brains work is something that neuroscientists have long sought to understand. The relationship is a complex one, but neuroscientists can be grateful to physicists for having developed a variety of instruments that have played a crucial role in shaping progress in the field. Scientists now have a range of techniques, including magnetic resonance imaging and positron emission tomography, that provide totally non-invasive "windows" into the brains of both healthy and diseased individuals.
One new technique in this area is "magnetoencephalography". Derived from the Greek word encephalon, or brain, the technique is used to detect the tiny magnetic fields generated from the weak electric impulses transmitted between brain cells. Magnetoencephalography, or MEG for short, allows human brain functions to be studied non-invasively at time resolutions of better than a millisecond, which is far quicker than other techniques. In MEG, cerebral magnetic fields are recorded with a "neuromagnetometer" that is positioned around the outside of the head. The underlying electrical activity of the brain that is responsible for the magnetic fields is then deduced by mathematical modelling.
MEG has been used mainly to study the way the brain processes signals, such as those arising from our sense of hearing, sight, touch, smell and pain, as well as those associated with voluntary movements of the body. The technique has also been used to examine the neural basis of more complex brain functions, such as attention, sensory memory and language.
More recently, neuroscientists have become excited about the possibility of using MEG to study the functional significance of "brain rhythms" - spontaneous electromagnetic oscillations, the most familiar of which is the 10 Hz "alpha rhythm" that originates in the vision-related areas at the back of the brain. MEG has also been used to study brain mechanisms in neurological diseases, to develop diagnostic tools that can help neurosurgeons before they operate, and to monitor changes in the central nervous system after the brain has been damaged or has been altered through extensive training in certain tasks.
In the May issue of Physics World magazine, Riitta Hari and Olli V Lounasmaa from Helsinki University of Technology explain how superconducting devices are allowing neuroscientists to measure tiny magnetic fields in the brain and obtain vital information on how neural signals are processed.