Biomagnetic approaches to studying the brain

Biomagnetic approaches to understanding the functional organization of the human brain include (1) transcranial magnetic stimulation (TMS), (2) magnetoencephalography (MEG) by superconducting quantum interference devices (SQUIDs), and (3) the imaging of electrical currents and impedance distributions of the head based on new principles of magnetic resonance imaging (MRI) techniques. These techniques are noninvasive and very useful for studying higher brain functions of humans such as memory and cognition. This article discusses these techniques, including the histories, principles, advantages, and disadvantages of each method, by using examples from studies recently conducted primarily in the author's laboratory.