Even snails and slugs can learn. The American neuroscientist Eric Kandel won a Nobel Prize for his
research on how learning works in the sea slug, Aplysia. These slugs have only a few thousand large
neurons, so Kandel was able to map out the connections among them and investigate the chemical
mechanisms responsible for the formations of these connections. Sea slugs don't learn much, but they
are able to modify such behaviors as eating and withdrawing from noxious stimuli. Kandel showed in
the 1960s how these behavioral changes result from changes in synapses, the connections between
neurons. For example, when a sea slug is exposed to a new substance and given an electric shock, its
neurons undergo chemical changes that alter its behavior, enabling it to avoid the substance.