  Magnetoencephalography (MEG) enables the study of brain activity by recording
the magnetic fields generated by neural currents and has become an important
technique for neuroscientists in research and clinical settings. Unlike the
liquid-helium cooled low-Tc superconducting quantum interference devices
(SQUIDs) that have been at the heart of modern MEG systems since their
invention, high-Tc SQUIDs can operate with liquid nitrogen cooling. The
relaxation of thermal insulation requirements allows for a reduction in the
stand-off distance between the sensor and the room-temperature environment from
a few centimeters to less than a millimeter, where MEG signal strength is
significantly higher. Despite this advantage, high-Tc SQUIDs have only been
used for proof-of-principle MEG recordings of well-understood evoked activity.
Here we show high-Tc SQUID-based MEG may be capable of providing novel
information about brain activity due to the close proximity of the sensor to
the head. We have performed single- and two-channel high-Tc SQUID MEG
recordings of spontaneous brain activity in two healthy human subjects. We
demonstrate modulation of the occipital alpha rhythm and the mu rhythm found in
the motor cortex. Furthermore, we have discovered uncharacteristically
high-amplitude activity in the theta-band from the occipital region of the
brain. Our results suggest high-Tc SQUIDs can provide a closer look into the
brain.
