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This Monday, October 6, the 2014 Nobel Prize in Medicine or Physiology was awarded to British and Norwegian neuroscientists for their groundbreaking research onto the neuronal mechanisms by which the brain allows us to map the space around us and navigate our surroundings.
John O’Keefe’s contribution stemmed from his 1971 discovery that the hippocampus of rats contained neurons that only activated when the animals were in a given corner of their room. Other cells nearby would fire up when the rat went to another place, leading O’Keefe to conclude that these “place cells” formed a map of the rat’s environment (O’Keefe and Dostrovsky, 1971).
May-Britt and Edvard Moser’s research took place three decades later: in 2005, they first reported cells in the rat’s entorhinal cortex, a brain region that acts as an interface between the hippocampus and the neocortex, whose activity waxed and waned depending on the location the rat was walking through. Crucially, these cells’ activities parcellate the space into a hexagonal grid, earning them the nickname “grid cells” (Hafting et al., 2005). Combined with other neurons in the entorhinal cortex that are sensitive to the direction in which the rat is headed, place and grid cells form a powerful localizing system.
A very similar system seems to be at work in human brains, as evidenced by micro-electrode recordings of single neurons in neurosurgical patients (Ekstrom et al., 2003; Jacobs et al., 2013). The human hippocampus and entorhinal cortex have famously been linked to the formation and initial storage of episodic memories (the memories of who we are and what we did). Neuroscientists have just started teasing out the links between our memories and the spatial navigation system of the hippocampal formation. This research will undoubtedly bring us further fascinating insights into the workings of our brains and minds.
O’Keefe J, Dostrovsky J. The hippocampus as a spatial map. Preliminary evidence from unit activity in the freely-moving rat. Brain Res. 1971 Nov;34(1):171-5. doi: 10.1016/0006-8993(71)90358-1
Hafting T, Fyhn M, Molden S, Moser MB, Moser EI. Microstructure of a spatial map in the entorhinal cortex. Nature. 2005 Aug 11;436(7052):801-6. Epub 2005 Jun 19. doi: 10.1038/nature03721
Ekstrom AD, Kahana MJ, Caplan JB, Fields TA, Isham EA, Newman EL, Fried I. Cellular networks underlying human spatial navigation. Nature. 2003 Sep 11;425(6954):184-8. doi: 10.1038/nature01964
Jacobs J, Weidemann CT, Miller JF, Solway A, Burke JF, Wei XX, Suthana N, Sperling MR, Sharan AD, Fried I, Kahana MJ. Direct recordings of grid-like neuronal activity in human spatial navigation. Nat Neurosci. 2013 Sep;16(9):1188-90. doi: 10.1038/nn.3466