The Nobel Prize for Physiology or Medicine was awarded this morning to John O’Keefe and May-Brit Moser and Edward Moser for the discovery of place cells and grid cells, respectively. O’Keefe discovered in 1971 that there were cells in the hippocampus that fired when a rat was in a certain location. He called these place cells and a whole generation of scientists, including the Mosers, have been studying them ever since then. In 2005, the Mosers discovered grid cells in the entorhinal cortex, which feed into the hippocampus. Grid cells fire whenever rats pass through periodically spaced intervals in a given area such as a room, dividing the room into a triangular lattice. Different grid cells have different frequencies, phases and orientations.
For humans, the hippocampus is an area of the brain known to be associated with memory formation. Much of what we know about the hippocampus in humans was learned by studying Henry Molaison, known as H.M. in the scientific literature, who had both of his hippocampi removed as a young man because of severe epileptic fits. H.M. could carry on a conversation but could not remember any of it if he was distracted. He had to be re-introduced to the medical staff that treated and observed him every day. H.M. showed us that memory comes in at least three forms. There is very short term or working memory, necessary to carry a conversation or remember a phone number long enough to dial it. Then there is long term explicit or declarative memory for which the hippocampus is essential. This is the memory of episodic events in your life and random learned facts about the world. People without a hippocampus, as depicted in the film Memento, cannot form explicit memories. Finally, there is implicit long term memory, such as how to ride a bicycle or use a pencil. This type of memory does not seem to require the hippocampus as evidenced by the fact that H.M. could become more skilled at certain games that he was taught to play daily even though he professed to never having played the game each time. The implication of the hippocampus for spatial location for humans is more recent. There was the famous study that showed London cab drivers had an enlarged hippocampus compared to controls and neural imaging has now shown something akin to place fields in humans.
While the three new laureates are all excellent scientists and deserving of the prize, this is still another example of how the Nobel prize singles out individuals at the expense of other important contributors. O’Keefe’s coauthor on the 1971 paper, Jonathan Dovstrosky, was not awarded. I’ve also been told that my former colleague at the University of Pittsburgh, Bill Skaggs, was the one who pointed out to the Mosers that the patterns in their data corresponded to grid cells. Bill was one of the most brilliant scientists I have known but did not secure tenure and is not directly involved in academic research anymore as far as I know. The academic system should find a way to maximize the skills of people like Bill and Douglas Prasher.
Finally, the hype surrounding the prize announcement is that the research could be important for treating Alzheimer’s disease, which is associated with a loss of episodic memory and navigational ability. However, if we use the premise that there must be a neural correlate of anything an animal can do, then place cells must necessarily exist given that rats have the ability to discern spatial location. What we did not know was where these cells are and O’Keefe showed us that it is in the hippocampus but we could have also associated the hippocampus with the memory loss of Alzheimer’s disease from H.M. The existence of grid cells is perhaps less obvious since it is not inherently obvious that we can naturally divide a room into a triangular lattice. It is plausible that grid cells do the computation giving rise to place cells but we still need to understand the computation that gives rise to grid cells. It is not obvious to me that grid cells are easier to compute than place cells.