Surprise

The write-up

What happens in the brain when expectations break. Unexpected events trigger a burst of noradrenaline from the locus coeruleus.

1. Exhibit A

   The locus coeruleus

   The LC is a small cluster of neurons in the brainstem's pons. It is the main source of the brain's noradrenaline, and its axons reach most of the brain.

2. Exhibit B

   Bursts for the unexpected

   Studies of deviant stimuli show brief bursts of LC activation, with noradrenaline released across the brain. The 2023 fMRI study tested whether different kinds of deviant stimuli all engage the LC, or whether other neuromodulatory systems respond too.

3. Exhibit C

   Not surprise-only

   LC activity tracks how behaviorally relevant a deviant stimulus is, and it is involved in arousal, attention and the sleep-wake cycle generally. It is not a dedicated 'surprise center'.

4. Exhibit D

   One name, two words

   Noradrenaline and norepinephrine are the same molecule. The Reel uses the American name.

5. Exhibit E

   Prediction

   The Reel's idea of comparing incoming information with predictions reflects a common way of modeling surprise as a mismatch, or prediction error, between expected and actual input.