How do mice get scared? - briefly
Mice react to danger by engaging neural circuits that release stress hormones, causing immediate freezing, rapid escape, or ultrasonic alarm calls. Visual, auditory, and olfactory signals—such as predator silhouettes, sudden sounds, or predator scent—trigger these defensive responses.
How do mice get scared? - in detail
Mice detect threats through a combination of sensory systems that feed rapid signals to the brain’s fear circuitry. Visual cues such as sudden movement or looming shadows activate retinal ganglion cells, which project to the superior colliculus and then to the amygdala. Auditory detection of high‑frequency sounds, especially ultrasonic squeaks produced by predators, is processed by the cochlear nucleus and relayed to the lateral amygdala. Olfactory receptors respond to predator odors (e.g., cat fur, fox urine), sending information through the olfactory bulb to the amygdalo‑hippocampal pathway.
Once the amygdala receives these inputs, it triggers a cascade of physiological and behavioral responses. The hypothalamic‑pituitary‑adrenal (HPA) axis releases corticosterone, raising blood glucose and preparing muscles for action. Simultaneously, the periaqueductal gray (PAG) coordinates motor outputs that manifest as freezing, rapid escape, or vigorous thigmotaxis (movement along walls).
Key components of the fear response include:
- Freezing: cessation of locomotion, reduced heart rate, heightened vigilance.
- Escape: sprinting toward shelter, increased respiration, activation of the sympathetic nervous system.
- Vigilant exploration: rapid scanning of the environment, elevated whisker movement for tactile sampling.
Genetic studies identify several genes that modulate these reactions. Mutations in Nr3c1 (glucocorticoid receptor) alter cortisol feedback, while variations in BDNF affect synaptic plasticity in the amygdala, influencing the intensity of fear learning. Optogenetic experiments demonstrate that selective activation of basolateral amygdala neurons can induce freezing in the absence of external threats.
Environmental factors shape the sensitivity of the fear system. Repeated exposure to mild stressors leads to habituation, decreasing the magnitude of freezing over time. Conversely, unpredictable or intense stressors produce sensitization, resulting in exaggerated escape behaviors and prolonged corticosterone elevation.
In summary, mice experience terror through integrated visual, auditory, and olfactory detection, rapid amygdala signaling, hormonal activation, and coordinated motor programs. Genetic and experiential variables fine‑tune the magnitude and duration of these responses.