ReviewA brief history of the resting state: The Washington University perspective
Introduction
It has been appreciated for at least two millennia that the brains of humans exhibit ongoing activity regardless of the presence or absence of any observable behaviors. As noted by Seneca in ~ 60 A.D., “The fact that the body is lying down is no reason for supposing that the mind is at peace. Rest is… far from restful” (Seneca, 1969). However, scientific investigation of the brain's “resting state” presents conceptual as well as methodological challenges whereas studying the brain's responses to controlled stimuli, that is, the experimental paradigm that has dominated systems neuroscience throughout the latter half of the 20th century, is comparatively straightforward. An expanded view of the tension between task-based and resting-state modes of investigation has been outlined in a recent review (Raichle, 2009). Below we present a brief account of scientific milestones that have shaped our view of the resting state. We then briefly review the history of resting state fMRI studies performed our laboratory.
Section snippets
“Resting state” defined
Given the apparently contradictory characterization of “rest” (see above) it is prudent to begin with a definition. In the context of experimentation, “rest” is an operational definition referring to a constant condition without imposed stimuli or other behaviorally salient events. The eyes may be closed or open, with or without visual fixation. The operational definition of “rest” may be generalized to encompass engagement in a controlled task as long as all imposed temporal structure is
Some history
The first scientist to explicitly address the significance of patterned nervous activity may have been Thomas Henry Huxley, in his book on the crayfish (Huxley, 1884). Huxley wrote, “If the nervous system were a mere bundle of nerve fibers extending between sensory organs and muscles, every muscular contraction would require the stimulation of that special point of the surface on which the appropriate sensory nerve ended. The contraction of several muscles at the same time, that is, the
Precursors of resting state fMRI
Spontaneous fluctuations in regional oxygen availability have been actively investigated since the 1950s (for an excellent review see, Hudetz et al., 1992). In retrospect, it is clear that these fluctuations represent the same physiology as spontaneous fluctuations of the BOLD signal (Ogawa et al., 1990, Pauling and Coryell, 1936) but the connection to fMRI was not established until much later (see also articles by Keith Thulborn, Peter Fox and Seiji Ogawa in this volume). In fact, these early
Resting state fMRI
It had been known since the advent of fMRI that the BOLD signal exhibits slow (nominally, < 0.1 Hz) spontaneous fluctuations although this phenomenon was initially regarded as noise (Purdon and Weisskoff, 1998). However, that these fluctuations are of neural origin was not established until Bharat Biswal and colleagues demonstrated that resting state BOLD signals are temporally correlated within the somatomotor system (Biswal et al., 1995). The neuroscience community, with few exceptions, was
Survey of resting state studies at the Washington University School of Medicine Neuroimaging Laboratories (NIL)
Seed-based correlation mapping is but one of several techniques used at the NIL to investigate the resting state. A comprehensive listing of all NIL papers on resting state activity published since 2005 is provided in Supplementary Information. Each paper is assigned to one or more related headings: Neuroscience; Analysis methodology; Mapping; Pathophysiology; Development and aging; State-dependent functional connectivity; Inter-individual differences; Review. These headings are briefly
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