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Biology session

The role of conditional stimuli associated with fear conditioning procedure in retrieval of memory
Varga Bence Tamás II. évfolyam
University of Veterinary Medicine Budapest, Department of Ecology
Supervisors: Dr. István Gyertyán, Dr. Erzsébet Hornung


The aim of our research group is to set up a complex cognitive test system that examines different animal models for different cognitive abilities. The set and coordinated models can later be used to test effective agents in cognitive impairments. In order to extend the already existing test system, setting up a model based on fear conditioning is my research objective. Fear conditioning models are focused on - as being a cardinal part of translational medicine - studying and possibly treating anxiety disorders such as post-traumatic stress syndrome (PTSD).

In fear conditioning, an aversive fearful stimulus, most often an electric shock, is associated with a discrete conditional stimulus (e.g. light or sound) (acquisition). The resulting fear memory can be tested in subsequent retrieval sessions where the conditioned stimuli are present, but the animals do not receive an electric shock. The strength of fear memory is deduced from the duration of the animals' freezing time.

In my BSc thesis, I found that the freezing time values of the groups conditioned by different discrete stimuli did not differ significantly from each other; and altering the wall pattern of the measuring box had subtle effect on the retrieval of fear memory. The work presented in this paper aimed at to investigate the extent to which the discrete conditional sound stimulus used during the acquisition and the contextual elements of the experimental procedure (measuring box, measuring room, person performing the measurement) contribute to recalling the fear memory. The new experiment consisting of 12 measurements, lasting for 1 month. The animals (24 Hannover Wistar rats) were divided into 3 groups ("non-shocked", "shocked-discrete", "shocked-context") according to their conditioning. During the 5 acquisition sessions, a mild electric shock was presented five times as an aversive stimulus, and during the 7 retention sessions, memory retrieval was examined at different times, in familiar and new contexts, with or without the associated sound stimulus.

According to our results, the sound stimulus can evoke fear memory in other contexts too, though to a lesser extent than in the original environment. Familiar context without sound stimuli did not cause a significant increase in freezing, however, after 3 weeks of intermission, the familiar context elicited partial but significant freezing, both with and without conditional stimuli. In the acquisition sessions, the freezing time increased in the pre-shock period and decreased immediately thereafter, while in the retention sessions, the freezing reaction showed a bell curve as a function of repetition of the sound stimulus.

Conclusions: (1) freezing was an anticipatory response, (2) in the short term, animals associated with the conditional stimulus and not with the environment, but after a longer period of memory consolidation, the context of the aversive experience was also tagged.

A kutatást a Nemzeti Agykutatási Program (NAP) támogatta #2017-1.2.1-NKP-2017-00002.

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