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Abstract:
Previously, researchers who used fMRI, PET, optical imaging, and NIRS techniques to map the
human brain regarded signal fluctuations at rest as noise.More recently, human imaging studies have
discovered that cerebral hemodynamic signals during the non-stimulated, resting state carry
meaningful information. These signals influence cortical evoked responses, and their variability
correlates with perception and behavior. Moreover, functional networks of cortical areas manifest
themselves through coherent fMRI signal fluctuations in the resting state. Therefore, it has been
suggested that fluctuations in the resting state are an important principle of brain function. However,
other reports expressed concerns with regard to the possibility that spontaneous fluctuations and
functional connectivity in the resting state could be caused by irrelevant physiological fluctuations
(e.g. respiration), vascular vaso-motion and imaging system noise. The degree in which spontaneous
fluctuations in hemodynamic signals reflect fluctuations in the underlying neuronal activity is a topic
of recent ongoing studies. The aim of the symposium is to bridge the gap between spontaneous
fluctuations in fMRI signals and their underlying neuronal activity. The symposiumwill be opened by
an overviewof studies on spontaneous fluctuations in fMRI signals and functional connectivity at rest.
Three talkswill follow, focusing on spontaneous fluctuations in neurophysiological signals at rest, and
howthey relate to fluctuations in hemodynamic signals. The symposiumwill describe the relationship
between these signals via a large-scale global view of the cortex (EEG-fMRI), as well as in specific
cortical regions via intra-cortical measurements in visual and motor areas. The neuronal correlates of
spontaneous fluctuations in hemodynamic signals will be demonstrated by measurements of high
spatial- and temporal resolution optical imaging using voltage sensitive dyes, neurophysiology and
simultaneous neurophysiology with fMRI in animal models. These neurophysiological signals cover
the range of membrane potentials, single and multi-unit activity, local field potentials, and mass neuronal activity.
