Eyeblink conditioning in rats.

Acquisition of eyeblink conditioned responses to a tone was studied in restrained male albino rats. Animals were placed in a modified restraining cage with their heads immobilized by surgically implanting a small bolt at the top of the skull and fastening it to the cage. Eyeblink responses were measured by a phototransistor which detected changes in the level of light reflected by eyelid closure. The conditioned stimulus was a 2,000-Hz, 90-dB, 500-ms tone; the unconditioned stimulus was a 4-psi, 150-ms air puff directed at the cornea; and the interstimulus interval was 350 ms, with a 60-s intertrial interval. Animals received 50 trials daily. All conditioned animals reached a criterion of 80% conditioned responses by Day 10. Pseudoconditioned control animals showed few conditioned responses by Day 10. The topography of the conditioned responses was comparable to those responses found with the nicitating membrane response in the rabbit. The data suggest that eyeblink conditioning in the rat can be used as a preparation to examine the attributes of classical conditioning as well as the neuroanatomical basis of associative learning.