A neurotransmitter and hormone involved in the body’s stress response and in memory formation.

Noradrenaline (also called norepinephrine, particularly in American literature) is released alongside cortisol during stressful events as part of the integrated stress response. The neurotransmitter acts both peripherally (raising heart rate, increasing alertness, mobilising energy) and centrally (modulating attention, arousal, and memory consolidation in the brain).

In the context of learning, noradrenaline’s most important function is its modulation of memory consolidation. Memories formed under noradrenergic activation are typically stronger and more durable than memories formed in calm states. This is part of the mechanism by which aversive training events can produce learning that lasts for years, and why a single bad experience can colour an animal’s response to a context for the rest of their life.

The mechanism is conserved across mammals and has been extensively studied in rodents, primates, and humans. The same basic principles apply across other mammalian species including horses, dogs, and cats, with smaller-scale research having confirmed the underlying mechanisms.

The implications for welfare-positive training are substantial. Training events that produce high noradrenergic activation (high arousal, stress, fear) tend to produce memories that are durable and inflexible. The animal may learn quickly under these conditions, but what they have learned is often not what the trainer intended (typically fear of the context rather than mastery of the task), and the learning is resistant to subsequent modification.

Calmer training, by contrast, produces memories that are less durable in the sense of being less rigidly encoded, but more flexible and more amenable to refinement and extension. The trade-off favours calm training in most contexts because flexibility and welfare outweigh rapid encoding.

This is one of the neurobiological grounds for the modern training consensus that training should keep the animal at moderate arousal levels rather than driving them into high-stress states.