Tiziano D'Albis: Models of spatial representation in the medial entorhinal cortex: the origin, inheritance, and amplification of grid-cell activity

ITB / HU-Berlin

High-level cognitive abilities such as memory, navigation, and decision making rely on the communication between the hippocampal formation and the neocortex. At the interface between these two brain regions is the entorhinal cortex, a multimodal association area where neurons with remarkable representations of self-location have been discovered: the grid cells.
Grid cells are neurons that fire according to the position of an animal in its environment. A single grid cell activates at multiple spatial locations with firing fields that are arranged in a strikingly-regular triangular pattern. Grid cells are thought to support animal’s navigation and spatial memory, but the cellular mechanisms that generate their patterns are still unknown. In this thesis, I study computational models of neural circuits to explain the emergence, inheritance, and amplification of grid-cell patterns.
In the first part of the thesis, I focus on the initial formation of grid firing fields. I embrace the idea that periodic representations of space could emerge via a competition between persistently-active spatial inputs and the reluctance of a neuron to fire for long stretches of time. Building upon previous theoretical work, I propose a single-cell model that generates grid-like activity solely form spatially-irregular inputs, spike-rate adaptation, and Hebbian synaptic plasticity. Compared to previous proposals, my model achieves a higher level of biological realism, gives unprecedented analytical insights, and generates novel experimental predictions.
In the second part of the thesis, I focus on the inheritance and amplification of grid-cell patterns. Motivated by the architecture of entorhinal microcircuits, I investigate how feed-forward and recurrent connections affect grid-cell tuning. I show that grids can be inherited across neuronal populations, and that both feed-forward and recurrent connections can improve the regularity of spatial firing. Finally, I show that a connectivity supporting these functions could self-organize in an unsupervised manner.
Altogether, this thesis contributes to a better understanding of the principles governing the neuronal representation of space in the medial entorhinal cortex.

Additional Information

PhD Defense

Organized by

Richard Kempter