Nature Reviews Neuroscience 8, 700-711 (September 2007) | doi:10.1038/nrn2201

Spontaneous fluctuations in brain activity observed with functional magnetic resonance imaging

Michael D. Fox1 & Marcus E. Raichle2  About the authors


The majority of functional neuroscience studies have focused on the brain's response to a task or stimulus. However, the brain is very active even in the absence of explicit input or output. In this Article we review recent studies examining spontaneous fluctuations in the blood oxygen level dependent (BOLD) signal of functional magnetic resonance imaging as a potentially important and revealing manifestation of spontaneous neuronal activity. Although several challenges remain, these studies have provided insight into the intrinsic functional architecture of the brain, variability in behaviour and potential physiological correlates of neurological and psychiatric disease.

Author affiliations

  1. Mallinckrodt Institute of Radiology, Washington University School of Medicine, 4525 Scott Avenue, St. Louis, Missouri 63110, USA.
  2. Departments of Neurology, Anatomy and Neurobiology and Biomedical Engineering, Washington University St. Louis, Missouri 63110, USA. Email:


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