Slow brain oscillations of sleep, resting state, and vigilance

Abstract

The most important quest of cognitive neuroscience may be to unravel the mechanisms by which the brain selects, links, consolidates, and integrates new information into its neuronal network, while preventing saturation to occur. During the past decade, neuroscientists working within several disciplines have observed an important involvement of the specific types of brain oscillations that occur during sleep—the cortical slow oscillations; during the resting state — the fMRI resting state networks including the default-mode network (DMN); and during task performance — the performance modulations that link as well to modulations in electroencephalography or magnetoencephalography frequency content.

Understanding the role of these slow oscillations thus appears to be essential for our fundamental understanding of brain function. Brain activity is characterized by oscillations occurring in spike frequency, field potentials or blood oxygen level-dependent functional magnetic resonance imaging signals. Environmental stimuli, reaching the brain through our senses, activate or inactivate neuronal populations and modulate ongoing activity. The effect they sort is to a large extent determined by the momentary state of the slow endogenous oscillations of the brain. In the absence of sensory input, as is the case during rest or sleep, brain activity does not cease. Rather, its oscillations continue and change with respect to their dominant frequencies and coupling topography. This chapter briefly introduces the topics that will be addressed in this dedicated volume of Progress in Brain Research on slow oscillations and sets the stage for excellent papers discussing their molecular, cellular, network physiological and cognitive performance aspects. Getting to know about slow oscillations is essential for our understanding of plasticity, memory, brain structure from synapse to DMN, cognition, consciousness, and ultimately for our understanding of the mechanisms and functions of sleep and vigilance.

Introduction

The brain is most often studied in paradigms that evaluate its response on stimuli. In the absence of stimuli, the brain by no means silences but rather shows prominent spontaneous fluctuations in activity. These fluctuations dramatically influence the neural network responses on input and thus information processing. The typical periodicity is due to the rhythmic discharge of large numbers of neurons that synchronize with frequencies ranging from 1 to over a 100 Hz, the frequencies that are usually observed in neurophysiological recordings of field potentials. This chapter focuses on even slower oscillations ‐ or fluctuations; the slow oscillations (0.5–1 Hz) of sleep and the infraslow oscillations (ISOs; 0.01–0.1 Hz) that have been found in time series of behavioral performance, of neuronal firing rates, of electroencephalography (EEG), of magnetoencephalography (MEG), and of functional magnetic resonance imaging (fMRI) blood oxygen level-dependent (BOLD) signal. These oscillations have been the topic of the 2010 Summer School of Brain Research in Amsterdam, the Netherlands, of which this dedicated volume of Progress in Brain Research accounts. This introductory chapter provides a bird's eye view on the relevance of slow oscillations and sets the stage for excellent papers discussing their molecular, cellular, network physiological and cognitive performance aspects.