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Julie Koenig (Korean Institute of Science and Technology)

Chasing the inputs that determine place cells firing

The spatial firing of hippocampal place cells constitutes one of the most striking behavioral correlates of neuronal activity in the mammalian brain but it is still not clear how hippocampal cells compute sharp place fields.

In a first set of experiments, we assessed the involvement of inputs from entorhinal grid cells on place cells firing. We established that during an inactivation of the medial septum, the periodic firing of grid cells was strongly affected while the spatial firing of place cells in a familiar as well as in a new environment was preserved. Septal inactivation also preserved the spatial firing of other types of entorhinal projection cells like border cells, and the directional firing of head direction cells, suggesting that these inputs can be sufficient to retrieve or form a spatial representation in the hippocampus.

Then, we were interested in the integration of different streams of information within the hippocampal networks. Mice were trained in a reward-position associations task while running on a belt mounted on a treadmill, in which place fields position could be controlled by the fixed visuo-tactile belt cues or by the variable position of the reward. First, our results indicate regional and neuronal-types differences in the integration of these two streams of information in pyramidal cells and interneurons of CA1 and CA3-dentate regions. Second, this integration seems to operate in a parallel manner as there was no clear temporal segregation of spikes from place fields controlled by the fixed belt cues or the position of the reward.