The key facts

  • After fear learning, the activity patterns of neurons in area CA1 of the mouse ventral hippocampus associated with threat and safety overlapped more strongly — contrary to the expectation that the representations would diverge further.
  • According to the authors' interpretation, the mechanism prioritizes speed of response: the brain gains faster access to a defensive program if the situation at least partly resembles a previous danger.
  • The researchers suggest a possible link between excessive activation of this mechanism and anxiety disorders and PTSD, but its role in humans remains to be established.

An unexpected experimental result

Scientists from McGill University and the University of Toronto published in the journal Nature Neuroscience a study on how the hippocampus — a brain region important for memory — distinguishes between similar situations with different emotional significance. Mice were trained to associate one setting with a threat and another with safety, after which the neural representations of these situations were compared, Gazeta.Ru reports.

Method: augmented reality and miniature microscopes

For observation, the researchers used an experimental arena with augmented reality: by changing visual and auditory cues, they switched the perceived setting without physically moving the animal. The activity of hundreds of neurons was recorded simultaneously with miniature microscopes.

Overlap instead of separation

It was expected that training would make the neural representations of the two situations more distinct. However, in the ventral part of the hippocampus, in area CA1, the opposite picture was found: the activity patterns associated with threat and safety began to overlap more strongly. According to the authors' interpretation, this mechanism prioritizes speed of reaction: if a new situation at least partly resembles a previous danger, the brain gains faster access to a defensive program. The cost of this strategy is the possibility of false alarms.

Possible link to anxiety disorders

The researchers suggest that excessive activation of this normal protective mechanism may be associated with anxiety disorders and post-traumatic stress disorder. However, its role in these conditions in humans, as noted in the publication, remains to be established. Separately, Gazeta.Ru mentions an earlier statement by neuroscientists that emotions are a 'theater for others' rather than what we actually feel; this piece was published by the same outlet and is not directly related to the hippocampus study.