Cross‐Modal transfer of the conditioned eyeblink response during interstimulus interval discrimination training in young rats

Abstract

Eyeblink classical conditioning (EBC) was observed across a broad developmental period with tasks utilizing two interstimulus intervals (ISIs). In ISI discrimination, two distinct conditioned stimuli (CSs; light and tone) are reinforced with a periocular shock unconditioned stimulus (US) at two different CS-US intervals. Temporal uncertainty is identical in design with the exception that the same CS is presented at both intervals. Developmental changes in conditioning have been reported in each task beyond ages when single-ISI learning is well developed. The present study sought to replicate and extend these previous findings by testing each task at four separate ages. Consistent with previous findings, younger rats (postnatal day -PD -23 and 30) trained in ISI discrimination showed evidence of enhanced cross-modal influence of the short CS-US pairing upon long CS conditioning relative to older subjects. ISI discrimination training at PD43-47 yielded outcomes similar to those in adults (PD65-71). Cross-modal transfer effects in this task therefore appear to diminish between PD30 and PD43-47. Comparisons of ISI discrimination with temporal uncertainty indicated that cross-modal transfer in ISI discrimination at the youngest ages did not represent complete generalization across CSs. ISI discrimination undergoes a more protracted developmental emergence than single-cue EBC and may be a more sensitive indicator of developmental disorders involving cerebellar dysfunction.

Limbic system development underlies the emergence of classical fear conditioning during the third and fourth weeks of life in the rat.

“…The older subjects also show greater contextual discrimination than the younger subjects, consistent with other work on generalization during development (i.e. Brown & Stanton, 2008). What is perhaps less commonly reported is that that older subjects also displayed enhanced auditory cue-induced freezing relative to the pre-weaning subjects, although this is a routine finding in our hands (Burman et al, 2014).…”

Neonatal pain and stress disrupts later‐life pavlovian fear conditioning and sensory function in rats: Evidence for a two‐hit model

“…For example, we observed differences in novel context freezing, consistent with a greater generalization across contexts in the younger animals. A greater generalization of learning in younger animals has been shown previously (Brown & Stanton, ). Also, we have previously published (Burman et al, ; Deal et al, ) that both auditory and contextual freezing emerge gradually prior to PND 24.…”

Using the context preexposure facilitation effect to study long-term context memory in preweanling, juvenile, adolescent, and adult rats

“…There was also a white opaque sheet covering any adjacent walls between two chambers so that the animals could not see each other. The alternate context consisted of wire mesh cages housed within BRS-LVE sound-attenuating shells used for eyeblink conditioning [6,36]. Preexposure sessions occurred in one of these two sets of chambers which were situated in two different rooms.…”