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Breakdown of Cortical Effective Connectivity During Sleep
Marcello Massimini,1,2Fabio Ferrarelli,1Reto Huber,1Steve K. Esser,1Harpreet Singh,1Giulio Tononi1*
When we fall asleep, consciousness fades yet the brain remainsactive. Why is this so? To investigate whether changes in corticalinformation transmission play a role, we used transcranial magneticstimulation together with high-density electroencephalographyand asked how the activation of one cortical area (the premotorarea) is transmitted to the rest of the brain. During quietwakefulness, an initial response (15 milliseconds) at the stimulationsite was followed by a sequence of waves that moved to connectedcortical areas several centimeters away. During non–rapideye movement sleep, the initial response was stronger but wasrapidly extinguished and did not propagate beyond the stimulationsite. Thus, the fading of consciousness during certain stagesof sleep may be related to a breakdown in cortical effectiveconnectivity.
1 Department of Psychiatry, University of Wisconsin, Madison, 6001 Research Park Boulevard, Madison, WI 53719, USA. 2 Department of Clinical Sciences, University of Milan, via G. B. Grassi 74, Milan 20157, Italy.
* To whom correspondence should be addressed. E-mail: gtononi{at}wisc.edu
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