After a strong aversive event, an organism reacts more vigorously to a mild stimulus that previously produced little response. Sensitization is that increase in responsiveness following exposure to a significant stimulus.

It is a form of non-associative learning, distinct from habituation. Sensitization can be short-term or long-term and is observed across species. In humans it appears in the heightened startle of post-traumatic stress and in certain chronic pain states. Cellular mechanisms involve changes in synaptic strength and excitability.

Sensitization prepares the organism for potential further threat. When it persists beyond the presence of danger, it becomes maladaptive. Understanding sensitization helps explain hypervigilance and the generalization of fear. It demonstrates that experience can amplify as well as diminish neural responses.

• Increased response after significant stimulation
• Non-associative form of learning
• Can be adaptive or pathological when prolonged
• Relevant to trauma and chronic pain