Abstract
SummarySleep spindles are major transient oscillations of the mammalian brain. Spindles are generated in the thalamus; however, what determines their duration is presently unclear. Here, we measured somatic activity of excitatory thalamocortical (TC) cells together with axonal activity of reciprocally coupled inhibitory reticular thalamic cells (nRTs) and quantified cycle-by-cycle alterations in their firing in vivo. We found that spindles with different durations were paralleled by distinct nRT activity, and nRT firing sharply dropped before the termination of all spindles. Both initial nRT and TC activity was correlated with spindle length, but nRT correlation was more robust. Analysis of spindles evoked by optogenetic activation of nRT showed that spindle probability, but not spindle length, was determined by the strength of the light stimulus. Our data indicate that during natural sleep a dynamically fluctuating thalamocortical network controls the duration of sleep spindles via the major inhibitory element of the circuits, the nRT.
Highlights
The large-scale activity of the brain is organized by a great variety of network oscillations, which temporally bind the activity of distinct cell populations
We found that spindles with different durations were paralleled by distinct nucleus reticularis thalami (nRT) activity, and nRT firing sharply dropped before the termination of all spindles
Both initial nRT and TC activity was correlated with spindle length, but nRT correlation was more robust
Summary
The large-scale activity of the brain is organized by a great variety of network oscillations, which temporally bind the activity of distinct cell populations. A major brain oscillation with variable length is the sleep spindle. These 1- to 3-s-long transient events have a frequency of 7–15 Hz and are most prevalent during stage II sleep. Spindle density shows strong correlation with memory performance (Fogel et al, 2007), problem-solving ability, and the general intelligence of an individual (Bodizs et al, 2005). Both the incidence and duration of spindles increase following learning (Morin et al, 2008) and decrease with age (Nicolas et al, 2001). Schizophrenia on the other hand is associated with a marked reduction of spindle length (Ferrarelli et al, 2007)
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