sensitization

Sensitization is a nonspecific phenomenon whereby repeated exposure to a stimulus results in the progressive enhancement of a response. The concept has been studied using the reflexes of animals such as Aplysia to better understand the underlying neural mechanisms. Research on sensitization includes a range of phenomena including drug sensitization and cross-sensitization, where a response is enhanced for a whole class of stimuli in addition to the original repeated stimulus. It has also been implicated in the pathologies of various health disorders.

==History== thumb|Aplysia with its siphon exposed on the posterior dorsal side. Eric Kandel was one of the first researchers to study the neural basis of sensitization, conducting experiments in the 1960s and 1970s on the gill withdrawal reflex of the sea slug Aplysia. Kandel and his colleagues first habituated the reflex, weakening the response by repeatedly touching the animal's siphon. They then paired noxious electrical stimulus to the tail with a touch to the siphon, causing the gill withdrawal response to reappear. After this sensitization, a light touch to the siphon alone produced a strong gill withdrawal response, and this sensitization effect lasted for several days. (After Squire and Kandel, 1999). In 2000, Eric Kandel was awarded the Nobel Prize in Physiology or Medicine for his research in neuronal learning processes.