Title: Hiroshi Ito, MPI for Brain Research
Start date: Jun 08 2018
Start time: 11:15 am
End time: 12:15 pm
Location: Max Planck House Lecture Hall

The hippocampus and associated parahippocampal structures are key elements of the brain circuit that enables animals to navigate to desired locations in space. Many neurons in this circuit, such as place cells or grid cells, fire when animals visit particular locations, suggesting that these neurons are part of an internal map of the environment. However, while place cells or grid cells provide accurate representations of the animal’s instantaneous position, such information alone is not sufficient for goal-directed navigation. Route planning requires encoding of not only current but also subsequent locations along trajectories. Our previous study has shown that information about upcoming trajectories in the CA1 area of the hippocampus is transferred from the medial prefrontal cortex (mPFC) through the thalamic nucleus reuniens (NR) that has strong projections to the CA1 region (Ito et al., Nature 2015). 

While such multiregional interactions are likely necessary for animals to perform complex goal-directed spatial navigation tasks, the interactions must be dynamic to cope with changing behavioral demands.  Cortical synchrony has been proposed as a mechanism for behavior-dependent functional coupling of neural circuits. We here report a key role for spike-time coordination in functional coupling of mPFC to the hippocampus through NR. When rats perform a T-maze alternation task, spikes of neurons in mPFC and NR exhibit enhanced coordination to the CA1 theta rhythm before the choice point on the maze. A similar coordination to CA1 theta rhythm was observed in neurons of the supramammillary nucleus (SUM). Optogenetic silencing of SUM neurons reduced the temporal coordination in the mPFC-NR-CA1 circuit. Following SUM inactivation, trajectory representations were impaired in both NR and CA1, but not in mPFC, indicating a failure in transmission of action plans from mPFC to the hippocampus. The findings identify theta-frequency spike-time coordination by a subcortical nucleus as a mechanism for gating of information flow in the mPFC-NR-CA1 circuit.

Host: Ryo Iwai