Systematic Variation of Acquisition Rate in Delay Eyelid Conditioning

Averaging artifacts inherent in group acquisition curves can mask behavioral phenomena that are potentially revealing in terms of underlying neural mechanisms. To address this, we implemented a behavioral analysis of 106 rabbits trained over 4 sessions using delay eyelid conditioning. Group results showed the typical monotonic increase in conditioned responses (CRs). For most subjects CRs first appeared (as indexed by the criterion of 8 CRs in 9 trials) during the first 18 trials of the second training session. Subdividing subjects according to the training block at which they met criterion revealed systematic differences in the subsequent rate that CR amplitudes increased, but not in asymptotic CR amplitudes. Subjects meeting criterion early in sessions showed more rapid increases in CR amplitude than those meeting criterion later in sessions. This effect was solely dependent on how early within a session criterion was met, as subjects meeting criterion at the beginning of the third and fourth sessions showed more rapid increases in CR amplitude than those meeting criterion after the first 18 trials of the second session. The exceptions were the 7% of the subjects that met criterion late in the first session. Their CR amplitudes increased at a rate similar to subjects meeting criterion early in sessions. These results suggest an interplay between consolidation processes and a previously reported short-term plasticity process that makes CR acquisition a nonmonotonic and complex function of the point during training sessions at which CRs first appear. (PsycINFO Database Record