Hippocampal and cerebellar single-unit activity during delay and trace eyeblink conditioning in the rat.

Full Abstract

In delay eyeblink conditioning, the CS overlaps with the US and only a brainstem-cerebellar circuit is necessary for learning. In trace eyeblink conditioning, the CS ends before the US is delivered and several forebrain structures, including the hippocampus, are required for learning, in addition to a brainstem-cerebellar circuit. The interstimulus interval (ISI) between CS onset and US onset is perhaps the most important factor in classical conditioning, but studies comparing delay and trace conditioning have typically not matched these procedures in this crucial factor, so it is often difficult to determine whether results are due to differences between delay and trace or to differences in ISI. In the current study, we employed a 580-ms CS-US interval for both delay and trace conditioning and compared hippocampal CA1 activity and cerebellar interpositus nucleus activity in order to determine whether a unique signature of trace conditioning exists in patterns of single-unit activity in either structure. Long-Evans rats were chronically implanted in either CA1 or interpositus with microwire electrodes and underwent either delay eyeblink conditioning, or trace eyeblink conditioning with a 300-ms trace period between CS offset and US onset. On trials with a CR in delay conditioning, CA1 pyramidal cells showed increases in activation (relative to a pre-CS baseline) during the CS-US period in sessions 1-4 that was attenuated by sessions 5-6. In contrast, on trials with a CR in trace conditioning, CA1 pyramidal cells did not show increases in activation during the CS-US period until sessions 5-6. In sessions 5-6, increases in activation were present only to the CS and not during the trace period. For rats with interpositus electrodes, activation of interpositus neurons on CR trials was present in all sessions in both delay and trace conditioning. However, activation was greater in trace compared to delay conditioning in the first half of the CS-US interval (during the trace CS) during early sessions of conditioning and, in later sessions of conditioning, activation was greater in the second half of the CS-US interval (during the trace interval). These results suggest that the pattern of hippocampal activation that differentiates trace from delay eyeblink conditioning is a slow buildup of activation to the CS, possibly representing encoding of CS duration or discrimination of the CS from the background context. Interpositus nucleus neurons show strong modeling of the eyeblink CR regardless of paradigm but show a changing pattern across conditioning that may be due to the necessary contributions of forebrain processing to trace conditioning.

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Author information

Author/s: Green, John T (JT); Arenos, Jeremy D (JD);

Affiliation: Department of Psychology, University of Vermont, Burlington VT 05405-0134, USA. john.green(-atsign-)uvm.edu

Grants: P20 RR016435-04 (Agency:NCRR NIH HHS) ; P20 RR016435-05 (Agency:NCRR NIH HHS) ; P20 RR16435 (Agency:NCRR NIH HHS) ; P20 RR16462 (Agency:NCRR NIH HHS)

Journal and publication information

Publication Type: Journal Article; Research Support, N.I.H., Extramural

Journal: Neurobiology of learning and memory (Neurobiol Learn Mem), published in United States. (Language: eng)

Reference: 2007-Feb; vol 87 (issue 2) : pp 269-84

Dates: Created 2007/01/10; Completed 2007/03/21; Revised 2008/11/20;

PMID: 17046292, status: MEDLINE (last retrieval date: 12/26/2008)

Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Action Potentials - physiology
Analysis of Variance
Animals
Cerebellum - cytology
Conditioning, Classical - physiology
Conditioning, Eyelid - physiology

Hippocampus - cytology
Male
Neurons - physiology
Rats
Rats, Long-Evans
Reaction Time - physiology

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