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Updated: Jul 5, 2026
Fear Incubation Using an Extended Fear-Conditioning Protocol for Rats
Published on: August 22, 2020
Long-term effect of cued fear conditioning on REM sleep microarchitecture in rats
Vibha Madan1, Francis X Brennan, Graziella L Mann
1Laboratory for Study of the Brain in Sleep, Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia 19104-6045, USA.
Study Objectives:
To study long-term effects of conditioned fear on REM sleep (REMS) parameters in albino rats.
Design:
We have investigated disturbances in sleep architecture, including muscle twitch density as REMS phasic activity, and freezing behavior in wakefulness, upon reexposure to a conditioned stimulus (CS) on Day 1 and Day 14 postconditioning.
Subjects:
Male Sprague-Dawley rats prepared for polysomnographic recordings.
Interventions:
After baseline sleep recording, the animals in the experimental group received five pairings of a 5-sec tone, co-terminating with a 1-sec, 1 mAfootshock. The control rats received similar numbers of tones and shocks, but explicitly unpaired. On postconditioning days, after reexposure to tones alone, sleep and freezing behavior were recorded.
Measurements And Results:
Conditioned fear significantly altered REMS microarchitecture (characterized as sequential-REMS [seq-REMS: < or =3 min episode separation] and single-REMS [sin-REMS: >3 min episode separation]) on Day 14. The total amount and number of seq-REMS episodes decreased, while the total amount and number of sin-REMS episodes increased. Further, the CS induced significant increases in freezing and REMS myoclonic twitch density in the experimental group. Reexposure to the CS produced no alterations in controls.
Conclusions:
The results suggest that conditioned fear causes REMS alterations, including difficulty in initiating a REMS episode as indicated by the diminution in the number of seq-REMS episodes. Another finding, the increase in phasic activity, agrees with the inference from clinical investigations that retrieval of fearful memories can be associated with the long-term REMS disturbances characteristic of posttraumatic stress disorder.
