Cortical Firing and Sleep Homeostasis

TLDR

Sleep homeostasis, the increase in sleep need with wakefulness and its dissipation during sleep, is well known, yet it is unclear whether cortical neuron firing rates change with the length of wake or sleep. The study aims to determine how prolonged wakefulness affects cortical neuron activity and to clarify the role of sleep in restoring normal firing patterns. After prolonged wakefulness, cortical neurons fire at higher rates, with shorter, more frequent ON periods and increased synchrony during early NREM sleep, while extended sleep reduces firing rates and synchrony and lengthens ON periods, and these firing pattern changes correlate with slow‑wave activity, demonstrating that increased firing during wakefulness is counterbalanced by sleep.

Abstract

The need to sleep grows with the duration of wakefulness and dissipates with time spent asleep, a process called sleep homeostasis. What are the consequences of staying awake on brain cells, and why is sleep needed? Surprisingly, we do not know whether the firing of cortical neurons is affected by how long an animal has been awake or asleep. Here, we found that after sustained wakefulness cortical neurons fire at higher frequencies in all behavioral states. During early NREM sleep after sustained wakefulness, periods of population activity (ON) are short, frequent, and associated with synchronous firing, while periods of neuronal silence are long and frequent. After sustained sleep, firing rates and synchrony decrease, while the duration of ON periods increases. Changes in firing patterns in NREM sleep correlate with changes in slow-wave activity, a marker of sleep homeostasis. Thus, the systematic increase of firing during wakefulness is counterbalanced by staying asleep.