1. Departments of Radiology,
2. Neurology,
3. Anatomy and Neurobiology, and,
4. Biomedical Engineering, Washington University in St Louis, Missouri 63110, USA
5. Department of Psychology, Center for Brain Science, Harvard University, Cambridge, Massachusetts 02138, USA
6. Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts 02129, USA

Correspondence to: M. E. Raichle^1,2,3,4 Correspondence and requests for materials should be addressed to M.E.R. (Email: marc@npg.wustl.edu).

Abstract

The traditional approach to studying brain function is to measure physiological responses to controlled sensory, motor and cognitive paradigms. However, most of the brain's energy consumption is devoted to ongoing metabolic activity not clearly associated with any particular stimulus or behaviour¹. Functional magnetic resonance imaging studies in humans aimed at understanding this ongoing activity have shown that spontaneous fluctuations of the blood-oxygen-level-dependent signal occur continuously in the resting state. In humans, these fluctuations are temporally coherent within widely distributed cortical systems that recapitulate the functional architecture of responses evoked by experimentally administered tasks^{2, 3, 4, 5, 6}. Here, we show that the same phenomenon is present in anaesthetized monkeys even at anaesthetic levels known to induce profound loss of consciousness. We specifically demonstrate coherent spontaneous fluctuations within three well known systems (oculomotor, somatomotor and visual) and the 'default' system, a set of brain regions thought by some to support uniquely human capabilities. Our results indicate that coherent system fluctuations probably reflect an evolutionarily conserved aspect of brain functional organization that transcends levels of consciousness.

1. Departments of Radiology,
2. Neurology,
3. Anatomy and Neurobiology, and,
4. Biomedical Engineering, Washington University in St Louis, Missouri 63110, USA
5. Department of Psychology, Center for Brain Science, Harvard University, Cambridge, Massachusetts 02138, USA
6. Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts 02129, USA

Correspondence to: M. E. Raichle^1,2,3,4 Correspondence and requests for materials should be addressed to M.E.R. (Email: marc@npg.wustl.edu).

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