Abstract
Simultaneous electroencephalography and functional magnetic resonance imaging (EEG–fMRI) studies have revealed brain activations time-locked to spindles. Yet, the functional significance of these spindle-related brain activations is not understood. EEG studies have shown that inter-individual differences in the electrophysiological characteristics of spindles (e.g., density, amplitude, duration) are highly correlated with “Reasoning” abilities (i.e., “fluid intelligence”; problem solving skills, the ability to employ logic, identify complex patterns), but not short-term memory (STM) or verbal abilities. Spindle-dependent reactivation of brain areas recruited during new learning suggests night-to-night variations reflect offline memory processing. However, the functional significance of stable, trait-like inter-individual differences in brain activations recruited during spindle events is unknown. Using EEG–fMRI sleep recordings, we found that a subset of brain activations time-locked to spindles were specifically related to Reasoning abilities but were unrelated to STM or verbal abilities. Thus, suggesting that individuals with higher fluid intelligence have greater activation of brain regions recruited during spontaneous spindle events. This may serve as a first step to further understand the function of sleep spindles and the brain activity which supports the capacity for Reasoning.
Highlights
Sleep spindles are one of the defining features of non-rapid eye movement (NREM) sleep
Among the 35 participants recruited in the study, only 5 participants did not meet the 5-min consolidated NREM sleep criteria for the sleep session, and one participant did not complete the Cambridge Brain Sciences (CBS) online test
Advancements in simultaneous EEG–fMRI technology and techniques has enabled the investigation of the functional brain activation recruited during well-known electrophysiological events such as sleep spindles
Summary
Sleep spindles are one of the defining features of non-rapid eye movement (NREM) sleep. Spindles are traditionally defined as bursts of waxing and waning neural oscillations between 11 and 16 Hz (Iber et al, 2007), which stand out from the ongoing, background electroencephalographic (EEG) activity (Rechtschaffen and Kales, 1968). The brain regions activated during spontaneous spindle events have been identified (Laufs et al, 2007; Schabus et al, 2007; Tyvaert et al, 2008; Andrade et al, 2011; Caporro et al, 2012). The functional significance of these brain activations has yet to be elucidated, thereby limiting our understanding of the function of sleep spindles. Spindles are remarkably stable from night-to-night, but vary considerably from one individual to another, and because of the trait-like nature of spindles (Silverstein and Levy, 1976), they have even been suggested to be an “electrophysiological fingerprint” (De Gennaro et al, 2005).
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