My latest paper, entitled ‘Navigating Cognition: Spatial Codes for Human Thinking’ just got published in Science. Together with Peter Gardenfors, Edvard Moser and Christian Doeller, I propose a theoretical framework for domain-general processing in the hippocampal-entorhinal region.
In this paper, we build upon findings from research on spatial navigation and merge them with a theory from cognitive science. Specifically, we propose place and grid cells in the hippocampus and entorhinal cortex, for the discovery of which John O’Keefe, May-Britt Moser and Edvard Moser were awarded the Nobel Prize in 2014, to not only map the space surrounding us for navigation, but to also map other dimensions of experience. Hippocampal place cells are usually active at only one specific location in an environment ; as opposed to grid cells in the entorhinal cortex which fire at many different positions that collectively form a regular, six-fold symmetric pattern . Similarly to positions in space, cells in the hippocampus and entorhinal cortex have been shown to represent specific time points during a waiting period [3-6], sound frequencies  or positions in visual space . Likewise, in neuroimaging studies of the human entorhinal cortex, grid-like hexadirectional signals were observed based on participants’ gaze direction [9,10]. Further, these patterns were also characteristic of entorhinal activity in participants retrieving knowledge about bird stimuli, which differed in the length of their necks and legs . In our new paper, we connect these exciting findings from neuroscience with a theory from cognitive science, developed by Peter Gardenfors , to propose that the hippocampus and entorhinal cortex use spatial coding principles to support human thinking.
We suggest that place and grid cells map cognitive spaces, similar to how they map space for navigation. If you think about a two-dimensional coordinate system, then each position corresponds to a certain value along the x- and the y-axis. Following the ideas put forward in the paper, the axes of these spaces can be based on our physical surroundings when we navigate, but also on abstract dimensions of our experience. For example, you can probably describe your friends based on what kind of jokes they like. Along this humor-axis, the individuals who like the same lame jokes will be located closer together and others, who are not a good laugh, would be positioned further away from them. Now this is only one dimension, but you could for example consider additionally how much your friends like to cook and form a two-dimensional space in which each friend has a position based on their joke preferences and their ambitions in the kitchen. In our paper, we describe that place and grid cells might encode positons in these cognitive spaces with their characteristic activity patterns.
We expand our framework around this central idea to incorporate important insights into how the hippocampal-entorhinal region functions. For example, the level of detail at which a space is represented differs between anatomical positions in the hippocampal formation, allowing knowledge to be available at different scales. For instance you can remember which friends like to cook and which never set foot into a kitchen, and, on a much more fine-grained level, differentiate among your friends who cook between those who consider themselves master chefs and those whose culinary aspirations stem merely from the necessity to eat.
Taken together, the theoretical framework we describe in this paper is based on the idea that the hippocampal-entorhinal region uses spatial coding principles to entertain cognitive spaces. This application of a theory from cognitive science could explain findings from physiology and neuroimaging that show the involvement of the hippocampus and entorhinal cortex in different domains of cognition and might prove useful for future studies aiming to understand the role of these brain regions.
O’Keefe, J., and Dostrovsky, J. (1971). The hippocampus as a spatial map. Preliminary evidence from unit activity in the freely-moving rat. Brain Res. 34, 171-175.
Hafting, T., Fyhn, M., Molden, S., Moser, M.-B., and Moser, E.I. (2005). Microstructure of a spatial map in the entorhinal cortex. Nature 436, 801-806.
Pastalkova, E., Itskov, V., Amarasingham, A., and Buzsáki, G. (2008). Internally Generated Cell Assembly Sequences in the Rat Hippocampus. Science 321, 1322-1327.
MacDonald, C.J., Carrow, S., Place, R., and Eichenbaum, H. (2013). Distinct Hippocampal Time Cell Sequences Represent Odor Memories in Immobilized Rats. J. Neurosci. 33, 14607-14616.
Kraus, B.J., Brandon, M.P., Robinson, R.J., Connerney, M.A., Hasselmo, M.E., and Eichenbaum, H. (2015). During Running in Place, Grid Cells Integrate Elapsed Time and Distance Run. Neuron 88, 578-589.
Eichenbaum, H. (2014). Time cells in the hippocampus: a new dimension for mapping memories. Nat. Rev. Neurosci. 15, 732-744.
Aronov, D., Nevers, R., and Tank, D.W. (2017). Mapping of a non-spatial dimension by the hippocampal-entorhinal circuit. Nature 543, 719-722.
Killian, N.J., Jutras, M.J., and Buffalo, E.A. (2012). A map of visual space in the primate entorhinal cortex. Nature 491, 761-764.
Nau, M., Navarro Schröder, T., Bellmund, J.L.S., and Doeller, C.F. (2018). Hexadirectional coding of visual space in human entorhinal cortex. Nat. Neurosci. 21, 188-190.
Julian, J.B., Keinath, A.T., Frazzetta, G., and Epstein, R.A. (2018). Human entorhinal cortex represents visual space using a boundary-anchored grid. Nat. Neurosci. 21, 191-194.
Constantinescu, A.O., O’Reilly, J.X., and Behrens, T.E.J. (2016). Organizing conceptual knowledge in humans with a gridlike code. Science 352, 1464-1468.
Gardenfors, P. (2000). Conceptual spaces: the geometry of thought (Cambridge, Mass: MIT Press).