This Brain Molecule Decides Which Memories Are Happy—or Terrible
Further evidence of this bias comes from the reaction of the mice when they were first put into learning situations. Before they knew whether the new associations would be positive or negative, the release of neurotensin from their thalamic neurons decreased. The researchers speculate that new stimuli are assigned a more negative valence automatically until their context is more certain and can redeem them.
“You’re more responsive to negative experiences versus positive experiences,” Hao Li said. If you almost get hit by a car, you’ll probably remember that for a very long time, but if you eat something delicious, that memory is likely to fade in a few days.
Ryan is more wary of extending such interpretations to humans. “We’re dealing with laboratory mice who are brought up in very, very impoverished environments and have very particular genetic backgrounds,” he said.
Still, he said it would be interesting to determine in future experiments whether fear is the actual default state of the human brain—and if that varies for different species, or even for individuals…