Functional magnetic resonance imaging (fMRI) can show most of the brain at work during a mental task, if data from large numbers of scans are averaged and different types of analysis are used.

fMRI is typically used by neuroscientists to identify just those few brain areas that are most active during a particular task. However, this approach might overlook important areas involved in cognitive processing, according to Javier Gonzalez-Castillo at the National Institute of Mental Health in Bethesda, Maryland, and his colleagues.

They imaged the brains of three people who had to decide whether a symbol flashed onto a flickering screen was a number or a letter. Averaging of the results from 100 scans revealed fMRI activations in 95% of the brain that were coincident with the task, varied in shape across regions, and clustered in a highly organized manner. This suggests that the signals may be functionally relevant rather than noise.

Proc. Natl Acad. Sci. USA (2012)