Characterisation of the sleep-related slow oscillation in the neocortical - entorhinal - hippocampal bidirectional circuit

• Author / Creator

  Wolansky, Trisha

• Our ability to recall information and events is astounding and dependent on the medial temporal lobe (MTL) memory system. The synaptic interconnections between the neocortex (nCTX), entorhinal cortex (EC), and hippocampus (HPC) are the anatomical basis of this memory system. The electrophysiological basis of memory formation in this system is largely unknown, but the activity patterns that occur during slow wave sleep (SWS) are thought to play an important role. One prominent activity pattern that occurs during SWS is the slow oscillation (SO). It is a large-amplitude rhythm of ~1Hz that was first described in the nCTX and only occurs during SWS and deep anaesthesia. Using the urethane-anaesthetised rat, I provide the first description of the SO in the HPC in Chapter 2. I found that the SO in the HPC was dynamically coordinated with that in the nCTX. Because the EC is the anatomical interface between the nCTX and HPC, I hypothesised that it could be responsible for this coordination. Chapter 3 characterises the SO in the EC and its coordination with both the nCTX and HPC. My results suggested that the synaptic interconnections between the nCTX and HPC via the EC were not solely responsible for SO coordination across these structures. Another possibility is that SO coordination across the nCTX, EC, and HPC occurs via the nucleus reuniens thalami (NReu). In Chapter 4, I delivered trains of electrical stimulation to the frontal cortex (fCTX) to enhance the SO in the nCTX and assess any effect in the HPC. In addition, I delivered the same stimulation trains directly to the medial prefrontal cortex (mpfCTX) and NReu. I found that repeated stimulation in each structure entrained the hippocampal SO. I also found that repeated stimulation of the fCTX and mpfCTX enhanced SO coordination across the nCTX and HPC, but repeated stimulation of the NReu did not. My results suggested that SO coordination across the nCTX and HPC occurs via both the EC and NReu. Understanding the coordination of SO activity across these structures will provide insight to the electrophysiological basis of the MTL memory system and the role of SWS in its function.

• Subjects / Keywords

  • Memory
  • Entorhinal cortex
  • Urethane
  • Slow wave sleep
  • Hippocampus

• Graduation date

  Fall 2009

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R36M66

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.