May-Britt Moser - Grid Cells And Cortical Maps For Space

A Nobel Laureate Lecture by May-Britt Moser: Spatial navigation and memory depend on brain structures such as the entorhinal cortex and the hippocampus. This has been known for more than a half century, since the groundbreaking studies of patient H.M. who had surgical damage to these structures. The lesion disturbed the ability to form episodic memories and to navigate successfully in space. John O’ Keefe was motivated by this information and explored the activity of hippocampal cells in the freely behaving rat. This way he discovered the place cells, cells that are active only at certain positions in the environment. Over the past 15-20 years, we have explored the wider circuit of the mammalian positioning system. In this lecture, I will show that the medial entorhinal cortex contains grid cells – cells with firing fields that tile environments in a periodic hexagonal pattern. The tiling of an environment by a grid cell is reminiscent of an internal coordinate system. These cells – which probably serve a metric function in the navigation system - are intermingled with other cells that respond to other features of navigation, such as where the animal goes and how fast it is moving. Today we know that the entorhinal space circuit contains both speed cells, border cells and head direction cells, in addition to grid cells. I will spend some time on the most recently discovered cell type – the speed cells – and show that running speed is represented in the firing rate of a ubiquitous but functionally dedicated population of medial entorhinal neurons. I will also show that speed is represented across a wider brain circuit that includes speed cells in the mesencephalic locomotor region, whose outputs may reach the medial entorhinal cortex via speed cells in the diagonal band of Broca. These multiple cell types of the entorhinal-hippocampal system are critical elements of a positioning system that dynamically monitors our changing location in the environment, and that may provide the spatial component of episodic memories. Poul Nissen, Professor and Director of the PUMPKIN Centre of the Danish National Research Foundation, and of DANDRITE, the Danish node of the Nordic-EMBL partnership for Molecular Medicine, Department of Molecular Biology, Aarhus University writes about the laureate: "May-Britt Moser and her husband Edvard Moser from the Norwegian Technical University in Trondheim, or “the Mosers” as they are referred to, form a world-famous team in the research of structures in the brain that process our spatial orientation and navigation. Especially their pioneering studies of "grid cells", which are activated during movement in relation to a hexagonal coordinate system of the field, have received highest acclaims and recognition in neurobiology and physiology. For this work, May-Britt and Edvard Moser received the Nobel Prize in Physiology / Medicine in 2014 together with John O’ Keefe from the University College London, who earlier had identified "place cells" in the hippocampus, the memory center of the brain. Later studies from the Moser laboratory have also concerned mechanisms of the perception and integration of the head orientation, physical boundaries of the field (through "border cells"), and movement (through "speed cells") in spatial orientation. The Mosers most often use rat as their animal model, since the rat through evolution has developed superb skills of direction and navigation in their intricate and typically dark habitats. The work of the Mosers is thus a beautiful example of basic research in the tradition of the Danish physiologist and Nobel laureate August Krogh, who stated that a physiological problem should be investigated in the animal model or tissue, where it is most pronounced." ________________________________________________________________________________________ Thumbnail photo by: Geir Vidar Nubdal