The neural circuitry underlying eyeblink conditioning in the rabbit, mouse and rat

Eyeblink conditioning is an associative learning paradigm in which an association is formed by the paired presentation of a neutral conditioned stimulus (CS), such as a tone, and an unconditioned stimulus (US), such as a corneal air puff or a periorbital shock. In the rabbit, cerebellum-brainstem circuitry plays an essential role in delay eyeblink conditioning, in which the US is delayed and terminates simultaneously with the CS. However, the neural mechanisms underlying delay eyeblink conditioning in mice and rats are unclear. In addition to cerebellum-brainstem circuitry, the amygdala is reportedly important for delay eyeblink conditioning in the mouse and rat. Here, we review the neural mechanisms underlying delay eyeblink conditioning in the rabbit, mouse, and rat, discussing relevant neural circuitry specific to mice and rats versus rabbits. We also review the neural circuitry underlying trace eyeblink conditioning, in which the CS and US are separated by a stimulus-free trace interval. The forebrain and cerebellar-brainstem circuitries are important for trace eyeblink conditioning in the rabbit, mouse, and rat. This review provides useful information for future research on eyeblink conditioning and for understanding neural substrates subserving learning and memory.