Detecting activity from deep brain areas with magnetoencephalographic arrays

Magnetoencephalographic (MEG) sensors detect with millisecond resolution current flow in the brain which is generated by tens of thousands of simultaneously active neurons. Arrays of sensors covering the entire scalp are now used to capture both temporal and topographic features of activity generated in multiple brain areas. The temporal information available with MEG compliments the excellent spatial resolution obtainable with other brain imaging technologies such as PET and fMRI. The majority of recent MEG studies have concentrated on the characterization of activity generated in relatively superficial fissural cortex. These brain areas are crucial for the initial processing of information from the senses and for the generation of movement. However, recent developments in MEG signal analysis now make possible the identification of responses from deep brain areas, such as hippocampus, thalamus and cerebellum. Many of these structures participate in a variety of higher cognitive functions, including learning and memory. The rational for and application of these new methods is demonstrated with whole-scalp MEG data recorded during the performance of a short-term memory task and tasks which interrogates the brain´s ability to detect changes in the temporal pattern of stimulus presentation