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During sleep, GABAergic inhibition of the thalamus occurs and along with that, it should "block" our senses. Are the receptors weakened, or completely shut down? If they are weakened, what is the exact process that can hinder their function? If they are completely shut, how can we still have the ability to hear during sleep and wake up as a result?

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Sleep research is a big field and the answer to your question can take many forms and fill libraries. Having said that, it is not so much inhibition of the thalamus per se, but a change in firing behavior that results in a decreased relay function of thalamic neurons afaik. Specifically, during stages of sleep, or in phases of reduced consciousness where thalamic relay of sensory inputs to the cortex is blocked, the thalamocortical neurons are entrained in slow oscillatory bursting behavior, resulting in more synchronized, slow-wave EEG (Fig. 1). This intrinsic slow wave, bursting activity in the thalamocortical network effectively reduces the ability for peripheral sensory input to reach the cortex via the thalamocortical fibers. This explains the unresponsiveness of people with slow wave EEG to external stimuli.

Slow-wave EEG is most prominent during deep sleep. By contrast, during active wakefulness these neurons fire more chaotically, very much dependent on their inputs, resulting in the EEG rich in high frequencies. A succinct overview is given here on the site of McGill University. Fig. 1 shows the dependency of thalamocortical neurons and cortical neurons in cats (Fig. 1A) and rodents (Fig. 1B) during different vigilance states. The figure is taken from a rock in sleep and epilepsy research, namely David McCormick.

Because the thalamocortical neurons are so occupied with their rhythmic bursting, phasic input from the thalamus may not be relayed. However, stimuli strong enough to push through / override the oscillatory behavior may still result in cortical activity in the sensory regions.

enter image description here Fig. 1. Slow wave sleep in cats (A) is associated with slow oscillations and spindle waves (equivalent to the K complex in man). The waking state is characterized by rhythmic activity at higher (gamma) frequency range. In mice (B), mere inactivity like cessation of walking is associated with an increase in slow rhythmic activity. (C) Schematic of thalamocortical circuitry responsible for the generation of rhythmic activity. The slow oscillation and gamma frequency oscillations are generated within the cortex, as an interaction of excitatory and inhibitory neurons. Spindle waves are generated during sleep in the thalamus as an interaction of thalamic reticular GABAergic neurons and thalamocortical relay cells. source: McCormick et al. (2014)

Reference
- McCormick et al., Curr Opin Neurobiol (2014); 31: 133-40

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