Understanding Sleep Function Through Patterns of Brain Activity

Sleep in the brain is distinguished from wake by the joint cycling of neurons through periods of intense activation followed by episodes of silence. This cycling produces slow wave activity (SWA), the EEG power between 0.5-4... [ view full abstract ]

Sleep in the brain is distinguished from wake by the joint cycling of neurons through periods of intense activation followed by episodes of silence. This cycling produces slow wave activity (SWA), the EEG power between 0.5-4 Hz during NREM sleep, that can be used as an electrophysiological marker of sleep need as it is shown to decrease with sleep and increase with time awake. Characterizing which physiological processes affect SWA, therefore, can reveal what biological activity generates sleep need. For example, wave amplitude, slope, and the average number of peaks per wave collectively reflect the number of neurons involved, the rate of recruitment, and the amount of synchrony present in an individual slow wave. We observed changes in these characteristics over the course of the light period in freely-behaving rats consistent with previous literature and a hypothesized sleep-dependent decline in synaptic strength. Following local cortical injection of zeta inhibitory peptide (ZIP), we observe similar alterations in these slow wave parameters, providing direct support for synaptic strength regulating neuronal synchrony during NREM sleep.  Additionally, these findings offer experimental support for synaptic strength modulating SWA and, more broadly, push us closer to understanding why we all need to sleep.