The role of the nucleus reuniens of the thalamus in the recognition memory network

Student thesis: Master's ThesisMaster of Science (MSc)

Abstract

Recognition memory provides the ability to judge if a stimulus has been encountered before. Depending on the type of information to be used for recognition, this process depends on a functional interaction between several brain regions including perirhinal cortex, hippocampus and medial prefrontal cortex. Recent studies have also implicated the nucleus reuniens of the thalamus (NRe) in recognition memory tasks with a high mnemonic demand, possibly by facilitating information flow between hippocampus and medial prefrontal cortex. Using Bayesian hierarchical modelling, the present study investigated if the NRe modulates neural activity within the recognition memory network.
Recognition memory of rats with a lesion in the NRe was compared to rats which received a sham surgery. Recognition memory was tested using a bow-tie maze task, in which rats explored either novel or highly familiar objects across a number of training sessions. Expression of the immediate early gene c-fos, a marker for neuronal activation, was measured in selected brain regions by immunohistochemistry. Levels of Fos-positive nuclei were assessed in the four experimental groups (Sham-Novel, Sham-Familiar, Lesion-Novel, Lesion-Familiar) using both standard frequentist statistics and Bayesian modelling. Analysis of object discrimination demonstrated that lesions in the NRe did not affect recognition memory performance and confirmed that both Sham-Familiar and Lesion-Familiar rats had encoded and recognised the repeatedly presented objects. Bayesian modelling outperformed frequentist statistics by estimating means with higher accuracy and reduced uncertainty. According to the Bayesian model, NRe lesions significantly affected Fos levels in the perirhinal cortex, TE2, dorsal peduncular cortex, CA3, dentate gyrus and subiculum.
The results suggest that the absence of the NRe alters neural activity in the recognition memory network when rats explore novel or familiar objects and presumably encode stimulus and associative information. While the precise role of the NRe in recognition memory remains to be defined, the present study supports the hypothesis that the NRe modulates information flow within the recognition memory network.
Date of Award1 Oct 2019
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorClea Warburton (Supervisor) & Cian O'Donnell (Supervisor)

Keywords

  • Recognition memory
  • nucleus reuniens of the thalamus
  • NRe
  • recognition memory network
  • Bayesian modelling
  • perirhinal cortex
  • hippocampus
  • medial prefrontal cortex
  • Bayesian hierarchical modelling

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