Ontogeny of eyeblink conditioning using a visual conditional stimulus

The developmental emergence of associative learning in rodents is determine d by intel actions among sensory, motor, and associative systems that are e ngaged in a particular experimental preparation (Carter & Stanton, 1996; Hu nt & Campbell, 1997; Rudy, 1992). In fear conditioning, chemosensory, audit ory, and visual cues emerge successively as effective conditional stimuli ( CS) during postnatal ontogeny. In the present study, we begin to examine th e generality of this principle of sensory system development for eyeblink c onditioning, a form of associative learning that develops substantially lat er than conditioned fear (Carter & Stanton, 1996). We asked whether the dev elopmental emergence of eyeblink conditioning to a visual CS occurs at an a ge that is the same or different from conditioning to an auditory CS. In Ex periment 1, rat pups were trained on postnatal Day 17 or 24 with experiment al parameters (and design) that were identical to our previous studies of e yeblink conditioning except that presentation of a light rather than a tone served as the CS. The outcome was also identical: no eyeblink conditioning on Day 17 and strong conditioning on Day 24. In Experiment 2, conditioning to tone versus light was directly compared by means of a discrimination le arning design on postnatal Days 19, 21, 23, and 31. There was no evidence f or differential development of auditory ver-sus visual eyeblink conditionin g. The difference between this outcome and previous ones involving conditio ned fear (Hunt & Campbell, 1997; Rudy, 1992) suggests that principles conce rning sensory maturation and learning may be different for early- versus la te-developing associative systems. (C) 1999 John Wiley & Sons, Inc.