Tristan Manfred Stöber successfully defended his PhD

On June 25, Tristan Manfred Stöber successfully defended his PhD thesis "Cooperate to compete—Identifying a potential role for hippocampal region CA2 in episodic memory formation".

Main research findings

To memorize an experience, our brain is replaying associated sequences of neuronal activity in the hippocamus and associated regions. Since we remember only a fraction of our experiences, the brain must have a way to prioritize certain neural activity sequences for replay.

This thesis outlines why and how interactions between hippocampal region CA2 and CA3 may play a decisive role in determining which sequences are reactivated. These interactions stand out for two reasons: First, synaptic plasticity at CA3 to CA2 projections is strongly regulated by neuromodulatory substances, which are likely released during emotionally arousing situations. Second, in both directions, excitatory activity in one region suppresses activity in the other region. Connecting these findings, I argue that neuromodulatory release can lead to selective pairing of co-active neural activity sequences across the two regions. Paired sequences may support each other's reactivation while suppressing competing sequences.

As shown by neural network simulations, such a pairing mechanism may be particularly beneficial for neural activity sequences comprised of few cells. As the number of recruited cells varies depending on the type of experience, the proposed CA2-CA3 sequence interaction may explain why CA2 is involved in some but not all situations.

The work has been conducted at Simula Research Laboratory and the University of Oslo.

Prior to the defence, Tristan Manfred Stöber presented his trial lecture "Sequences and action in the motor cortex: Experiments and models".

The PhD defence and trial lecture were fully digital.

Adjudication committee:

  • Principal Investigator Thomas McHugh, Laboratory for Circuit and Behavioral Physiology, Japan
  • Professor Henning Sprekeler, Institute of Software Engineering and Theoretical Computer Science, Technishe Unversität Berlin, Germany
  • Associate Professor Sjannie Lefevre Nilsson, Department of Biosciences, University of Oslo, Norway

Supervisors

  • Professor Marianne Fyhn, Department of Biosciences, University of Oslo
  • Associate Professor Arvind Kumar, KTH Royal Institute of Technology, Stockholm
  • Associate Professor Trygve Solstad, NTNU
  • Associate Professor Jill Leutgeb, University of California San Diego

Chair of defence

  • Professor and Head of Department Stephan Oepen, Department of Informatics, University of Oslo