Why does a rat tremble when you stroke its back? - briefly
The trembling is a stress‑induced reflex caused by activation of the sympathetic nervous system, which triggers muscle tension and shivering. Gentle handling reduces this response by lowering arousal and calming the animal’s nervous system.
Why does a rat tremble when you stroke its back? - in detail
Rats often display a rapid shivering motion when their dorsal fur is brushed. The reaction originates from mechanoreceptors located in the skin and hair follicles. These receptors convert the tactile stimulus into electrical signals that travel via the dorsal spinal cord to the somatosensory cortex. Simultaneously, the signal engages the autonomic nervous system, particularly the sympathetic branch, which prepares the animal for a potential threat.
The sympathetic activation releases catecholamines such as norepinephrine. Elevated catecholamine levels increase muscle tone and produce involuntary contractions, perceived as trembling. In laboratory measurements, corticosterone concentrations rise within minutes of a back‑stroke, confirming a stress‑related hormonal response.
Several factors influence the intensity of the tremor:
- Stimulus strength – firm, rapid strokes generate larger receptor responses than gentle, slow ones.
- Previous handling experience – rats accustomed to human contact show reduced shaking.
- Environmental context – bright lighting or noisy surroundings amplify the sympathetic output.
- Individual variability – genetic strain and age affect baseline stress reactivity.
Research using electromyography demonstrates that the tremor consists of low‑amplitude, high‑frequency bursts in the axial muscles. These bursts cease when the stimulus is removed or when the animal becomes habituated through repeated, predictable stroking sessions.
For practical handling, apply light, consistent strokes and allow the rat to adjust over several minutes. Repeated exposure diminishes the sympathetic surge, leading to calmer behavior and the disappearance of the shaking response.