What happens in your brain when you go under general anaesthesia?

Updated

General anaesthetics rapidly suppress brainstem arousal, block thalamic relay to cortex, and disintegrate cortical networks including prefrontal and posterior cingulate, causing unconsciousness. The hippocampus is also inhibited, preventing memory formation.

Brainstem, Thalamus, Prefrontal Cortex, Hippocampus lit up on the Brain Atlas 3D brain: what happens in your brain when you go under general anaesthesia
Figure. The brain regions that light up when you go under general anaesthesia, in order: Brainstem (sedation begins), then Thalamus (sensory gate closes), then Prefrontal Cortex (executive silence), then Hippocampus (amnesia sets in).

Watch it light up on the 3D brain

Brain regions that light up

OrderRegionWhat it does here
1BrainstemAnaesthetic molecules reach the brainstem and depress arousal nuclei, reducing wakefulness.
2ThalamusThalamic activity drops, cutting off sensory information from reaching the cortex.
3Prefrontal CortexPrefrontal cortex activity plummets, impairing awareness and decision-making.
4HippocampusThe hippocampus stops encoding new memories, causing amnesia for the procedure.

1. Brainstem: sedation begins

Step 1 of what happens in your brain when you go under general anaesthesia: Brainstem lit on the Brain Atlas 3D brain
Figure 1. Brainstem, sedation begins: Anaesthetic molecules reach the brainstem and depress arousal nuclei, reducing wakefulness.

The brainstem's ascending reticular activating system, including noradrenergic and cholinergic nuclei, normally keeps the cortex awake. Anaesthetics enhance inhibitory GABA signalling and suppress these nuclei, causing sedation and decreased responsiveness.

2. Thalamus: sensory gate closes

Step 2 of what happens in your brain when you go under general anaesthesia: Brainstem, Thalamus lit on the Brain Atlas 3D brain
Figure 2. Thalamus, sensory gate closes: Thalamic activity drops, cutting off sensory information from reaching the cortex.

As the main relay station, the thalamus normally forwards sensory signals to the cortex. Anaesthetics hyperpolarise thalamic neurons, reducing their firing and disrupting thalamocortical communication, which contributes to loss of consciousness.

3. Prefrontal Cortex: executive silence

Step 3 of what happens in your brain when you go under general anaesthesia: Brainstem, Thalamus, Prefrontal Cortex lit on the Brain Atlas 3D brain
Figure 3. Prefrontal Cortex, executive silence: Prefrontal cortex activity plummets, impairing awareness and decision-making.

The prefrontal cortex is critical for conscious thought and self-awareness. Anaesthetic-induced inhibition reduces its activity and connectivity with other regions, leading to the absence of conscious experience.

4. Hippocampus: amnesia sets in

Step 4 of what happens in your brain when you go under general anaesthesia: Brainstem, Thalamus, Prefrontal Cortex, Hippocampus lit on the Brain Atlas 3D brain
Figure 4. Hippocampus, amnesia sets in: The hippocampus stops encoding new memories, causing amnesia for the procedure.

Anaesthetics inhibit hippocampal neurons and disrupt synaptic plasticity, preventing the consolidation of new experiences. This ensures patients do not remember surgery, even if some awareness occurred.

Good to know

  • General anaesthesia is a drug-induced, reversible coma, not natural sleep.
  • The thalamus is thought to act as a gate for consciousness, and its suppression is a hallmark of anaesthetic-induced unconsciousness.
  • Different anaesthetics act on different receptors, but many enhance GABA-A receptor activity.

General anaesthesia vs natural sleep

Unlike sleep, where the brain cycles through stages and can be aroused by strong stimuli, anaesthesia produces a deeper, more uniform suppression of brain activity. Sleep involves active brain processes like memory consolidation; anaesthesia essentially turns off cortical integration, with little dreaming and minimal rapid eye movement.

Test yourself

  1. Which brain region is most directly responsible for reducing sensory relay during anaesthesia?

  2. General anaesthesia produces amnesia primarily by inhibiting which structure?

  3. How does general anaesthesia differ from natural sleep?

0 of 3 answered · 0 correct

Simplified: many regions work together at once, and this shows the main players in the order they act. For learning only, not medical advice.