Sensitization is a non-associative learning process in which repeated administration of a stimulus results in the progressive amplification of a response.
Eric Kandel was one of the first to study the neural basis of sensitization, conducting experiments in the 1960s and 1970s on the gill withdrawal reflex of the seaslug Aplysia.
They then paired noxious electrical stimulus to the tail with a touch to the siphon, causing the gill withdrawal response to reappear.
In 2000, Eric Kandel was awarded the Nobel Prize in Physiology or Medicine for his research in neuronal learning processes.
The neural basis of behavioral sensitization is often not known, but it typically seems to result from a cellular receptor becoming more likely to respond to a stimulus.