Fearful stimuli trigger a range of behaviors in rat (each represented by a different color). Image credit: Kristina M. Wright (CCBY 4.0)
Knowing that an animal is fearful is crucial for many psychology and neuroscience studies. For instance, this knowledge allows researchers to examine the brain pathways involved in processing and responding to fear.
Typically, researchers consider that a rodent is experiencing fear if it ‘freezes’ – a response which, in the wild, helps to evade detection by predators. In Pavlovian fear conditioning experiments, for example, rats and mice freeze when exposed to a stimulus (often a specific sound) previously associated with unpleasant sensations. However, rodents can also respond more actively to threats, for instance by running or jumping away. It remains unclear whether the ‘fearful stimuli’ used in Pavlovian approaches specifically elicits only freezing, or other fear-related behaviors as well.
To investigate this, Chu et al. used high-speed cameras to record rats’ responses to a sound cue they had ‘learned’ to associate with a mild foot shock. In addition to freezing, the animals ran, jumped, stood on their hind legs and stopped their usual reward-seeking behavior in response to the cue. Crucially, these reactions were absent when the rats were exposed to sound cues not associated with pain.
Overall, these experiments demonstrate that Pavlovian conditioning can elicit a full range of fear-related behaviors beyond freezing. Understanding the neural activity behind these diverse responses could lead to more targeted therapies and interventions addressing the various ways stress and anxiety manifest in people.
