Short‐lasting conditioned stimulus applied to the middle cerebellar peduncle elicits delayed conditioned eye blink responses in the decerebrate ferret

Abstract

In delay eye blink conditioning, the conditioned stimulus (CS) ends at the time of the unconditioned stimulus (US). If the CS duration is decreased, there will be a 'trace' period with no ongoing CS before the onset of the US. During this period some neural activity has to continue after the CS offset to: (i) permit association between the CS and the US; and (ii) elicit a conditioned response appearing after the CS offset. In this study we test the role of the cerebellum in maintaining CS activity required for eliciting a conditioned response after the CS offset. Decerebrate ferrets were trained in a delay conditioning paradigm with an electrical stimulation of the forelimb as CS and of the periorbital area as US. The conditioned responses in the upper eyelid were monitored with electromyographical techniques. In well-trained animals, test CSs of short duration down to 0.2 ms were applied to the forelimb or the middle cerebellar peduncle, while the interstimulus interval between CS onset and US onset was kept constant at 300 ms. Test CSs of short duration applied to the forelimb elicited conditioned responses. More importantly, also a short-lasting CS to the middle cerebellar peduncle could elicit conditioned responses. The results indicate that precerebellar CS pathways are not required for maintaining the neural activity that elicits conditioned responses after the CS offset. It is suggested that neurons maintaining such activity are located in the cerebellum, either the cortex alone or the cortex and the deep nuclei.

Memory trace and timing mechanism localized to cerebellar Purkinje cells

“…Furthermore, in agreement with previous findings on both overt and Purkinje cell conditioned responses (27,16) using mossy fiber conditional stimuli, we observed the same response on posttraining probe trials whether we delivered eight pulses over 17.5 ms, 31 pulses over 300 ms, or 81 pulses over 800 ms, to the parallel fibers, suggesting that the temporal profile of the conditioned Purkinje cell response is determined by the initial part (less than 20 ms) of the conditional stimulus and therefore is insensitive to any temporally patterned input during the main part of the interstimulus interval and conditioned response (Fig. 2 B-D).…”

Learned response sequences in cerebellar Purkinje cells

“…We have previously found, after training with single ISIs, that a mossy fiber CS lasting only a few milliseconds or tens of milliseconds can elicit a full-blown, accurately timed PcCR (19), as well as a complete and accurately timed blink CR (20). If the sequential PcCR is a single response unit, then a CS that elicits the early components could potentially also elicit the later ones.…”

“…If they are composites of separate components, then it should be possible to learn each component independently. Conversely, if it is a single response unit, then the whole sequence conceivably also could be elicited with shorter versions of the CS, as has previously been shown for single PcCRs (19) and eyeblink CRs (20).…”

Neural Substrates of Eyeblink Conditioning: Acquisition and Retention

“…Stimulation of the mcp itself is an effective CS (Steinmetz 1990a;Svensson and Ivarsson 1999), and lesion of the interpositus nucleus abolishes the CR established with a pontine or middle peduncle stimulation CS ). When animals are trained using electrical stimulation of the pontine nuclei as a CS (corneal airpuff US), some animals show immediate and complete transfer of the behavioral CR and of the learning-induced neural responses in the interpositus nucleus to a tone CS (Steinmetz 1990b) and complete transfer from peripheral CSs to mossy fiber stimulation in the mcp (Hesslow et al 1999).…”