Infraslow oscillations modulate excitability and interictal epileptic activity in the human cortex during sleep

doi:10.1073/pnas.0305375101

Infraslow oscillations modulate excitability and interictal epileptic activity in the human cortex during sleep

^*Department of Biosciences, University of Helsinki, P.O. Box 65, University of Helsinki, 00014 Helsinki, Finland; ^†Department of Clinical Neurophysiology, University of Helsinki, 00014 Helsinki, Finland; and ^§Regional Epilepsy Center, Department of Neurology, University of Washington and Harborview Medical Center, Box 359745, 325 Ninth Avenue, Seattle, WA 98104

Edited by Marcus E. Raichle, Washington University School of Medicine, St. Louis, MO, and approved February 8, 2004 (received for review September 11, 2003)

Abstract

Human cortical activity has been intensively examined at frequencies ranging from 0.5 Hz to several hundred Hz. Recent studies have, however, reported also infraslow fluctuations in neuronal population activity, magnitude of electroencephalographic oscillations, discrete sleep events, as well as in the occurrence of interictal events. Here we use direct current electroencephalography to demonstrate large-scale infraslow oscillations in the human cortex at frequencies ranging from 0.02 to 0.2 Hz. These oscillations, which are not detectable in conventional electroencephalography because of its limited recording bandwidth (typical lower limit 0.5 Hz), were observed in widespread cortical regions. Notably, the infraslow oscillations were strongly synchronized with faster activities, as well as with the interictal epileptic events and K complexes. Our findings suggest that the infraslow oscillations represent a slow, cyclic modulation of cortical gross excitability, providing also a putative mechanism for the as yet enigmatic aggravation of epileptic activity during sleep.

Footnotes

↵ ‡ To whom correspondence should be addressed. E-mail: sampsa.vanhatalo{at}helsinki.fi.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: EEG, electroencephalography; ISO, infraslow oscillation; DC, direct current; IIE, interictal epileptiform event; FIR, finite impulse response; SWS, slow wave sleep.